New data-driven estimation of terrestrial CO2 fluxes in Asia using a standardized database of eddy covariance measurements, remote sensing data, and support vector regression

Science.gov (United States)

Ichii, Kazuhito; Ueyama, Masahito; Kondo, Masayuki; Saigusa, Nobuko; Kim, Joon; Alberto, Ma. Carmelita; Ardö, Jonas; Euskirchen, Eugénie S.; Kang, Minseok; Hirano, Takashi; Joiner, Joanna; Kobayashi, Hideki; Marchesini, Luca Belelli; Merbold, Lutz; Miyata, Akira; Saitoh, Taku M.; Takagi, Kentaro; Varlagin, Andrej; Bret-Harte, M. Syndonia; Kitamura, Kenzo; Kosugi, Yoshiko; Kotani, Ayumi; Kumar, Kireet; Li, Sheng-Gong; Machimura, Takashi; Matsuura, Yojiro; Mizoguchi, Yasuko; Ohta, Takeshi; Mukherjee, Sandipan; Yanagi, Yuji; Yasuda, Yukio; Zhang, Yiping; Zhao, Fenghua

2017-04-01

The lack of a standardized database of eddy covariance observations has been an obstacle for data-driven estimation of terrestrial CO2 fluxes in Asia. In this study, we developed such a standardized database using 54 sites from various databases by applying consistent postprocessing for data-driven estimation of gross primary productivity (GPP) and net ecosystem CO2 exchange (NEE). Data-driven estimation was conducted by using a machine learning algorithm: support vector regression (SVR), with remote sensing data for 2000 to 2015 period. Site-level evaluation of the estimated CO2 fluxes shows that although performance varies in different vegetation and climate classifications, GPP and NEE at 8 days are reproduced (e.g., r2 = 0.73 and 0.42 for 8 day GPP and NEE). Evaluation of spatially estimated GPP with Global Ozone Monitoring Experiment 2 sensor-based Sun-induced chlorophyll fluorescence shows that monthly GPP variations at subcontinental scale were reproduced by SVR (r2 = 1.00, 0.94, 0.91, and 0.89 for Siberia, East Asia, South Asia, and Southeast Asia, respectively). Evaluation of spatially estimated NEE with net atmosphere-land CO2 fluxes of Greenhouse Gases Observing Satellite (GOSAT) Level 4A product shows that monthly variations of these data were consistent in Siberia and East Asia; meanwhile, inconsistency was found in South Asia and Southeast Asia. Furthermore, differences in the land CO2 fluxes from SVR-NEE and GOSAT Level 4A were partially explained by accounting for the differences in the definition of land CO2 fluxes. These data-driven estimates can provide a new opportunity to assess CO2 fluxes in Asia and evaluate and constrain terrestrial ecosystem models.

Conditional CO2 flux analysis of a managed grassland with the aid of stable isotopes

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Zeeman, M. J.; Tuzson, B.; Emmenegger, L.; Knohl, A.; Buchmann, N.; Eugster, W.

2009-04-01

Short statured managed ecosystems, such as agricultural grasslands, exhibit high temporal changes in carbon dioxide assimilation and respiration fluxes for which measurements of the net CO2 flux, e.g. by using the eddy covariance (EC) method, give only limited insight. We have therefore adopted a recently proposed concept for conditional EC flux analysis of forest to grasslands, in order to identify and quantify daytime sub-canopy respiration fluxes. To validate the concept, high frequency (≈5 Hz) stable carbon isotope analyis of CO2 was used. We made eddy covariance measurements of CO2 and its isotopologues during four days in August 2007, using a novel quantum cascade laser absorption spectrometer, capable of high time resolution stable isotope analysis. The effects of a grass cut during the measurement period could be detected and resulted in a sub-canopy source conditional flux classification, for which the isotope composition of the CO2 could be confirmed to be of a respiration source. However, the conditional flux method did not work for an undisturbed grassland canopy. We attribute this to the flux measurement height that was chosen well above the roughness sublayer, where the natural isotopic tracer (δ13C) of respiration was too well mixed with background air.

Quantifying and reducing the differences in forest CO₂-fluxes estimated by eddy covariance, biometric and chamber methods: A global synthesis

Energy Technology Data Exchange (ETDEWEB)

Wang, Xingchang; Wang, Chuankuan; Bond-Lamberty, Benjamin

2017-12-15

Carbon dioxide (CO₂) fluxes between terrestrial ecosystems and the atmosphere are primarily measured with eddy covariance (EC), biometric, and chamber methods. However, it is unclear why the estimates of CO₂-fluxes, when measured using these different methods, converge at some sites but diverge at others. We synthesized a novel global dataset of forest CO₂-fluxes to evaluate the consistency between EC and biometric or chamber methods for quantifying CO₂ budget in forests. The EC approach, comparing with the other two methods, tended to produce 25% higher estimate of net ecosystem production (NEP, 0.52Mg C ha-1 yr-1), mainly resulting from lower EC-estimated Re; 10% lower ecosystem respiration (Re, 1.39Mg C ha-1 yr-1); and 3% lower gross primary production (0.48 Mg C ha-1 yr-1) The discrepancies between EC and the other methods were higher at sites with complex topography and dense canopies versus those with flat topography and open canopies. Forest age also influenced the discrepancy through the change of leaf area index. The open-path EC system induced >50% of the discrepancy in NEP, presumably due to its surface heating effect. These results provided strong evidence that EC produces biased estimates of NEP and Re in forest ecosystems. A global extrapolation suggested that the discrepancies in CO₂ fluxes between methods were consistent with a global underestimation of Re, and overestimation of NEP, by the EC method. Accounting for these discrepancies would substantially improve the our estimates of the terrestrial carbon budget .

CO2 fluxes from a tropical neighborhood: sources and sinks

Science.gov (United States)

Velasco, E.; Roth, M.; Tan, S.; Quak, M.; Britter, R.; Norford, L.

2011-12-01

Cities are the main contributors to the CO2 rise in the atmosphere. The CO2 released from the various emission sources is typically quantified by a bottom-up aggregation process that accounts for emission factors and fossil fuel consumption data. This approach does not consider the heterogeneity and variability of the urban emission sources, and error propagation can result in large uncertainties. In this context, direct measurements of CO2 fluxes that include all major and minor anthropogenic and natural sources and sinks from a specific district can be used to evaluate emission inventories. This study reports and compares CO2 fluxes measured directly using the eddy covariance method with emissions estimated by emissions factors and activity data for a residential neighborhood of Singapore, a highly populated and urbanized tropical city. The flux measurements were conducted during one year. No seasonal variability was found as a consequence of the constant climate conditions of tropical places; but a clear diurnal pattern with morning and late afternoon peaks in phase with the rush-hour traffic was observed. The magnitude of the fluxes throughout daylight hours is modulated by the urban vegetation, which is abundant in terms of biomass but not of land-cover (15%). Even though the carbon uptake by vegetation is significant, it does not exceed the anthropogenic emissions and the monitored district is a net CO2 source of 20.3 ton km-2 day-1 on average. The carbon uptake by vegetation is investigated as the difference between the estimated emissions and the measured fluxes during daytime.

Eddy Covariance measurements of stable CO2 and H2O isotopologues

Science.gov (United States)

Braden-Behrens, Jelka; Knohl, Alexander

2015-04-01

The analysis of the stable isotope composition of CO2 and H2O fluxes (such as 13C, 18O and 2H in H2O and CO2) has provided valuable insights into ecosystem gas exchange. The approach builds on differences in the isotope signature of different ecosystem components that are primarily caused by the preference for or the discrimination against respective isotope species by important processes within the ecosystem (e.g. photosynthesis or leaf water diffusion). With the ongoing development of laser spectrometric methods, fast and precise measurements of isotopologue mixing ratios became possible, hence also enabling Eddy Covariance (EC) based approaches to directly measure the isotopic composition of CO2 and H2Ov net fluxes on ecosystem scale. During an eight month long measurement campaign in 2015, we plan to simultaneously measure CO2 and H2Ov isotopologue fluxes using an EC approach in a managed beech forest in Thuringia, Germany. For this purpose, we will use two different laser spectrometers for high frequency measurements of isotopic compositions: For H2Ov measurements, we will use an off axis cavity output water vapour isotope analyser (WVIA, Los Gatos Research Inc.) with 5 Hz response; and for CO2 measurements, we will use a quantum cascade laser-based system (QCLAS, Aerodyne Research Inc.) with thermoelectrically cooled detectors and up to 10 Hz measurement capability. The resulting continuous isotopologue flux measurements will be accompanied by intensive sampling campaigns on the leaf scale: Water from leaf, twig, soil and precipitation samples will be analysed in the lab using isotope ratio mass spectrometry. During data analysis we will put a focus on (i) the influence of carbon and oxygen discrimination on the isotopic signature of respective net ecosystem exchange, (ii) on the relationship between evapotranspiration and leaf water enrichment, and (iii) on the 18O exchange between carbon dioxide and water. At present, we already carried out extensive

Inferring CO2 Fluxes from OCO-2 for Assimilation into Land Surface Models to Calculate Net Ecosystem Exchange

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Prouty, R.; Radov, A.; Halem, M.; Nearing, G. S.

2016-12-01

Investigations of mid to high latitude atmospheric CO2 show a growing seasonal amplitude. Land surface models poorly predict net ecosystem exchange (NEE) and are unable to substantiate these sporadic observations. An investigation of how the biosphere has reacted to changes in atmospheric CO2 is essential to our understanding of potential climate-vegetation feedbacks. A global, seasonal investigation of CO2-flux is then necessary in order to assimilate into land surface models for improving the prediction of annual NEE. The Atmospheric Radiation Measurement program (ARM) of DOE collects CO2-flux measurements (in addition to CO2 concentration and various other meteorological quantities) at several towers located around the globe at half hour temporal frequencies. CO2-fluxes are calculated via the eddy covariance technique, which utilizes CO2-densities and wind velocities to calculate CO2-fluxes. The global coverage of CO2 concentrations as provided by the Orbiting Carbon Observatory (OCO-2) provide satellite-derived CO2 concentrations all over the globe. A framework relating the satellite-inferred CO2 concentrations collocated with the ground-based ARM as well as Ameriflux stations would enable calculations of CO2-fluxes far from the station sites around the entire globe. Regression techniques utilizing deep-learning neural networks may provide such a framework. Additionally, meteorological reanalysis allows for the replacement of the ARM multivariable meteorological variables needed to infer the CO2-fluxes. We present the results of inferring CO2-fluxes from OCO-2 CO2 concentrations for a two year period, Sept. 2014- Sept. 2016 at the ARM station located near Oklahoma City. A feed-forward neural network (FFNN) is used to infer relationships between the following data sets: F([ARM CO2-density], [ARM Meteorological Data]) = [ARM CO2-Flux] F([OCO-2 CO2-density],[ARM Meteorological Data]) = [ARM CO2-Flux] F([ARM CO2-density],[Meteorological Reanalysis]) = [ARM CO2-Flux

Elucidating Carbon Exchange at the Regional Scale Via Airborne Eddy Covariance Flux Measurements

Science.gov (United States)

Hannun, R. A.; Wolfe, G. M.; Kawa, S. R.; Newman, P. A.; Hanisco, T. F.; Diskin, G. S.; DiGangi, J. P.; Nowak, J. B.; Barrick, J. D. W.; Thornhill, K. L., II; Noormets, A.; Vargas, R.; Clark, K. L.; Kustas, W. P.

2017-12-01

Direct flux observations from aircraft provide a unique tool for probing greenhouse gas (GHG) sources and sinks on a regional scale. Airborne eddy covariance, which relies on high-frequency, simultaneous measurements of fluctuations in concentration and vertical wind speed, is a robust method for quantifying surface-atmosphere exchange. We have assembled and flown an instrument payload onboard the NASA C-23 Sherpa aircraft capable of measuring CO2, CH4, H2O, and heat fluxes. Flights for the Carbon Airborne Flux Experiment (CARAFE) took place during September 2016 and May 2017 based out of Wallops Flight Facility, VA. Flight tracks covered a variety of ecosystems and land-use types in the Mid-Atlantic, including forests, croplands, and wetlands. Carbon fluxes are derived using eddy covariance and wavelet analysis. Our results show a strong drawdown of CO2 and near-zero CH4 emissions from crops and dry-land forest, but seasonally strong CH4 flux from wetland forest. CARAFE flux data will also be compared with observations from several flux towers along the flight path to complement the airborne measurements. We will further assess the effects of land surface type and seasonal variability in carbon exchange. Regional-scale flux observations from CARAFE supply a useful constraint for improving top-down and bottom up estimates of carbon sources and sinks.

[Characteristics of CO2 flux before and in the heating period at urban complex underlying surface area].

Science.gov (United States)

Jia, Qing-yu; Zhou, Guang-sheng; Wang, Yu; Liu, Xiao-mei

2010-04-01

Urban areas were significant contributors to global carbon dioxide emissions. The eddy covariance (EC) was used to measure carbon dioxide (CO2) concentration and flux data at urban area in Shenyang. This research analyzed the characteristics of atmospheric CO2 concentration and flux in October 2008 to November 2008 period before and in the heating period. The results showed that the daily variation of CO2 concentration was two-peak curve. The first peak time appeared as same as sunrise time, while the second peak time impacted by vehicles and heating. The result of CO2 flux showed that urban atmospheric CO2 was net emissions, vegetation photosynthesis absorbed CO2 of traffic, the CO2 flux peak appeared at 17:15-18:15 in the heating period, CO2 emission increased 29.37 g x (m2 x d)(-1) in the heating period than that before the heating period; there was corresponding relationship between CO2 flux and the time when temperature peak and sensible heating flux (Hc) turn positive. The results also indicated that atmospheric CO2 concentration and its flux were affected seriously by both wind direction and carbon sources.

Estimating surface CO2 fluxes from space-borne CO2 dry air mole fraction observations using an ensemble Kalman Filter

Directory of Open Access Journals (Sweden)

S. Dance

2009-04-01

Full Text Available We have developed an ensemble Kalman Filter (EnKF to estimate 8-day regional surface fluxes of CO2 from space-borne CO2 dry-air mole fraction observations (XCO2 and evaluate the approach using a series of synthetic experiments, in preparation for data from the NASA Orbiting Carbon Observatory (OCO. The 32-day duty cycle of OCO alternates every 16 days between nadir and glint measurements of backscattered solar radiation at short-wave infrared wavelengths. The EnKF uses an ensemble of states to represent the error covariances to estimate 8-day CO2 surface fluxes over 144 geographical regions. We use a 12×8-day lag window, recognising that XCO2 measurements include surface flux information from prior time windows. The observation operator that relates surface CO2 fluxes to atmospheric distributions of XCO2 includes: a the GEOS-Chem transport model that relates surface fluxes to global 3-D distributions of CO2 concentrations, which are sampled at the time and location of OCO measurements that are cloud-free and have aerosol optical depths 2 profiles to XCO2, accounting for differences between nadir and glint measurements, and the associated scene-dependent observation errors. We show that OCO XCO2 measurements significantly reduce the uncertainties of surface CO2 flux estimates. Glint measurements are generally better at constraining ocean CO2 flux estimates. Nadir XCO2 measurements over the terrestrial tropics are sparse throughout the year because of either clouds or smoke. Glint measurements provide the most effective constraint for estimating tropical terrestrial CO2 fluxes by accurately sampling fresh continental outflow over neighbouring oceans. We also present results from sensitivity experiments that investigate how flux estimates change with 1 bias and unbiased errors, 2 alternative duty cycles, 3 measurement density and correlations, 4 the spatial resolution of estimated flux estimates, and 5 reducing the length of the lag window and the

Comparison of eddy covariance and modified Bowen ratio methods for measuring gas fluxes and implications for measuring fluxes of persistent organic pollutants

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D. J. Bolinius

2016-04-01

Full Text Available Semi-volatile persistent organic pollutants (POPs cycle between the atmosphere and terrestrial surfaces; however measuring fluxes of POPs between the atmosphere and other media is challenging. Sampling times of hours to days are required to accurately measure trace concentrations of POPs in the atmosphere, which rules out the use of eddy covariance techniques that are used to measure gas fluxes of major air pollutants. An alternative, the modified Bowen ratio (MBR method, has been used instead. In this study we used data from FLUXNET for CO2 and water vapor (H2O to compare fluxes measured by eddy covariance to fluxes measured with the MBR method using vertical concentration gradients in air derived from averaged data that simulate the long sampling times typically required to measure POPs. When concentration gradients are strong and fluxes are unidirectional, the MBR method and the eddy covariance method agree within a factor of 3 for CO2, and within a factor of 10 for H2O. To remain within the range of applicability of the MBR method, field studies should be carried out under conditions such that the direction of net flux does not change during the sampling period. If that condition is met, then the performance of the MBR method is neither strongly affected by the length of sample duration nor the use of a fixed value for the transfer coefficient.

CO2 Fluxes and Concentrations in a Residential Area in the Southern Hemisphere

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Weissert, L. F.; Salmond, J. A.; Turnbull, J. C.; Schwendenmann, L.

2014-12-01

While cities are generally major sources of anthropogenic carbon dioxide (CO2) emissions, recent research has shown that parts of urban areas may also act as CO2 sinks due to CO2 uptake by vegetation. However, currently available results are related to a large degree of uncertainty due to the limitations of the applied methods and the limited number of studies available from urban areas, particularly from the southern hemisphere. In this study, we explore the potential of eddy covariance and tracer measurements (13C and 14C isotopes of CO2) to quantify and partition CO2 fluxes and concentrations in a residential urban area in Auckland, New Zealand. Based on preliminary results from autumn and winter (March to July 2014) the residential area is a small source of CO2 (0.11 mol CO2 m-2 day-1). CO2 fluxes and concentrations follow a distinct diurnal cycle with a morning peak between 7:00 and 9:00 (max: 0.25 mol CO2 m-2 day-1/412 ppm) and midday low with negative CO2 fluxes (min: -0.17 mol CO2 m-2 day-1/392 ppm) between 10:00 and 15:00 local time, likely due to photosynthetic CO2 uptake by local vegetation. Soil CO2 efflux may explain that CO2 concentrations increase and remain high (401 ppm) throughout the night. Mean diurnal winter δ13C values are in anti-phase with CO2 concentrations and vary between -9.0 - -9.7‰. The depletion of δ13C compared to clean atmospheric air (-8.2‰) is likely a result of local CO2 sources dominated by gasoline combustion (appr. 60%) during daytime. A sector analysis (based on prevailing wind) of CO2 fluxes and concentrations indicates lower CO2 fluxes and concentrations from the vegetation-dominated sector, further demonstrating the influence of vegetation on local CO2 concentrations. These results provide an insight into the temporal and spatial variability CO2 fluxes/concentrations and potential CO2 sinks and sources from a city in the southern hemisphere and add valuable information to the global database of urban CO2 fluxes.

Comparison of Landfill Methane Oxidation Measured Using Stable Isotope Analysis and CO2/CH4 Fluxes Measured by the Eddy Covariance Method

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Xu, L.; Chanton, J.; McDermitt, D. K.; Li, J.; Green, R. B.

2015-12-01

Methane plays a critical role in the radiation balance and chemistry of the atmosphere. Globally, landfill methane emission contributes about 10-19% of the anthropogenic methane burden into the atmosphere. In the United States, 18% of annual anthropogenic methane emissions come from landfills, which represent the third largest source of anthropogenic methane emissions, behind enteric fermentation and natural gas and oil production. One uncertainty in estimating landfill methane emissions is the fraction of methane oxidized when methane produced under anaerobic conditions passes through the cover soil. We developed a simple stoichiometric model to estimate methane oxidation fraction when the anaerobic CO2 / CH4 production ratio is known, or can be estimated. The model predicts a linear relationship between CO2 emission rates and CH4 emission rates, where the slope depends on anaerobic CO2 / CH4 production ratio and the fraction of methane oxidized, and the intercept depends on non-methane-dependent oxidation processes. The model was tested using carbon dioxide emission rates (fluxes) and methane emission rates (fluxes) measured using the eddy covariance method over a one year period at the Turkey Run landfill in Georgia, USA. The CO2 / CH4 production ratio was estimated by measuring CO2 and CH4 concentrations in air sampled under anaerobic conditions deep inside the landfill. We also used a mass balance approach to independently estimate fractional oxidation based on stable isotope measurements (δ13C of methane) of gas samples taken from deep inside the landfill and just above the landfill surface. Results from the two independent methods agree well. The model will be described and methane oxidation will be discussed in relation to wind direction, location at the landfill, and age of the deposited refuse.

The Effect of Breaking Waves on CO_2 Air-Sea Fluxes in the Coastal Zone

Science.gov (United States)

Gutiérrez-Loza, Lucía; Ocampo-Torres, Francisco J.; García-Nava, Héctor

2018-03-01

The influence of wave-associated parameters controlling turbulent CO_2 fluxes through the air-sea interface is investigated in a coastal region. A full year of high-quality data of direct estimates of air-sea CO_2 fluxes based on eddy-covariance measurements is presented. The study area located in Todos Santos Bay, Baja California, Mexico, is a net sink of CO_2 with a mean flux of -1.3 μmol m^{-2}s^{-1} (-41.6 mol m^{-2}yr^{-1} ). The results of a quantile-regression analysis computed between the CO_2 flux and, (1) wind speed, (2) significant wave height, (3) wave steepness, and (4) water temperature, suggest that the significant wave height is the most correlated parameter with the magnitude of the flux but the behaviour of the relation varies along the probability distribution function, with the slopes of the regression lines presenting both positive and negative values. These results imply that the presence of surface waves in coastal areas is the key factor that promotes the increase of the flux from and into the ocean. Further analysis suggests that the local characteristics of the aqueous and atmospheric layers might determine the direction of the flux.

CO2 Fluxes Monitoring at the Level of Field Agroecosystem in Moscow Region of Russia

Science.gov (United States)

Meshalkina, Joulia; Mazirov, Ilya; Samardzic, Miljan; Yaroslavtsev, Alexis; Valentini, Riccardo; Vasenev, Ivan

2014-05-01

The Central Russia is still one of the less GHG-investigated European areas especially in case of agroecosystem-level carbon dioxide fluxes monitoring by eddy covariance method. The eddy covariance technique is a statistical method to measure and calculate vertical turbulent fluxes within atmospheric boundary layers. The major assumption of the metod is that measurements at a point can represent an entire upwind area. Eddy covariance researches, which could be considered as repeated for the same area, are very rare. The research has been carried out on the Precision Farming Experimental Field of the Russian Timiryazev State Agricultural University (Moscow, Russia) in 2013 under the support of RF Government grant No. 11.G34.31.0079. Arable derno-podzoluvisls have around 1 The results have shown high daily and seasonal dynamic of agroecosystem CO2 emission. Sowing activates soil microbiological activity and the average soil CO2 emission and adsorption are rising at the same time. CO2 streams are intensified after crop emerging from values of 3 to 7 μmol/s-m2 for emission, and from values of 5 to 20 μmol/s-m2 for adsorption. Stabilization of the flow has come at achieving plants height of 10-12 cm. The vegetation period is characterized by high average soil CO2 emission and adsorption at the same time, but the adsorption is significantly higher. The resulted CO2 absorption during the day is approximately 2-5 times higher than emissions at night. For example, in mid-June, the absorption value was about 0.45 mol/m2 during the day-time, and the emission value was about 0.1 mol/m2 at night. After harvesting CO2 emission is becoming essentially higher than adsorption. Autumn and winter data are fluctuate around zero, but for some periods a small predominance of CO2 emissions over the absorption may be observed. The daily dynamics of CO2 emissions depends on the air temperature with the correlation coefficient changes between 0.4 and 0.8. Crop stage, agrotechnological

Variation in agricultural CO2 fluxes during the growing season, collected from more than ten eddy covariance towers in the Mississippi Delta Region

Science.gov (United States)

Runkle, B.; Suvocarev, K.; Reba, M. L.; Novick, K. A.; White, P.; Anapalli, S.; Locke, M. A.; Rigby, J.; Bhattacharjee, J.

2016-12-01

Agriculture is unique as an anthropogenic activity that plays both a large role in carbon and water cycling and whose management activities provide a key opportunity for responses to climate change. It is therefore especially crucial to bring field observations into the modeling community, test remote sensing products, encourage policy debate, and enable carbon offsets markets that generate revenue and fund climate-smart activities. The accurate measurement of agricultural CO2 exchange - both primary productivity and ecosystem respiration - in concert with evapotranspiration provides crucial information on agro-ecosystem functioning and improves our predictive capacity for estimating the impacts of climate change. In this study we report field measurements from more than 10 eddy covariance towers in the Lower Mississippi River Basin taken during the summer months of 2016. Many towers, some recently deployed, are being aggregated into a regional network known as Delta-Flux, which will ultimately include 15-20 towers by 2017. Set in and around the Mississippi Delta Region within Louisiana, Arkansas, and Mississippi, the network will collect flux, micrometeorological, and crop yield data in order to construct estimates of regional CO2 exchange. These time-series data are gap-filled using statistical and process-based models to generate estimates of summer CO2 flux. The tower network is comprised of sites representing widespread agriculture production, including rice, cotton, corn, soybean, and sugarcane; intensively managed pine forest; and bottomland hardwood forest. Unique experimental production practices are represented in the network and include restricted water use, bioenergy, and by-product utilization. Several towers compose multi-field sites testing innovative irrigation or management practices. Current mapping of agricultural carbon exchange - based on land cover layers and fixed crop emission factors - suggests an unconstrained carbon flux estimate in this

Eddy covariance N2O flux measurements at low flux rates: results from the InGOS campaign in a Danish willow field.

Science.gov (United States)

Ibrom, Andreas; Brümmer, Christian; Hensen, Arjan; van Asperen, Hella; Carter, Mette S.; Gasche, Rainer; Famulari, Daniela; Kutsch, Werner; Pilegaard, Kim; Ambus, Per

2014-05-01

Nitrous oxide (N2O) fluxes from soils are characterised by their high spatial and temporal variability. The fluxes depend on the availability of the substrates for nitrification and denitrification and soil physical and chemical conditions that control the metabolic microbial activity. The sporadic nature of the fluxes and their high sensitivity to alterations of the soil climate put very high demands on measurement approaches. Laser spectroscopy enables accurate and fast response detection of atmospheric N2O concentrations and is used for eddy covariance (EC) flux measurements. Alternatively N2O fluxes can be measured with chambers together with high precision analysers. Differences in the measurement approaches and system designs are expected to have a considerable influence on the accuracy of the flux estimation. This study investigates how three different eddy covariance systems perform in a situation of low N2O fluxes from a flat surface. Chamber flux measurements with differing chamber and analyser designs are used for comparison. In April 2013, the EU research infrastructure project InGOS (http://www.ingos-infrastructure.eu/) organised a campaign of N2O flux measurements in a willow plantation close to the Risø Campus of the Technical University of Denmark. The willow field was harvested in February 2013 and received mineral fertiliser equivalent to 120 kg N ha-1 before the campaign started. Three different eddy covariance systems took part in the campaign: two Aerodyne quantum cascade laser (QCL) based systems and one Los Gatos Research off-axis integrated-cavity-output spectroscopy (ICOS) system for N2O and CO. The sonic anemometers were all installed at 2 m height above the bare ground. Gill R3 type sonic anemometers were used with QCL systems and a Gil HS-50 with the ICOS system. The 10 Hz raw data were analysed with group specific softwares and procedures. The local conditions in the exceptionally cold and dry spring 2013 did not lead to large N2O flux

Evaluation of a lower-powered analyzer and sampling system for eddy-covariance measurements of nitrous oxide fluxes

Directory of Open Access Journals (Sweden)

S. E. Brown

2018-03-01

Full Text Available Nitrous oxide (N2O fluxes measured using the eddy-covariance method capture the spatial and temporal heterogeneity of N2O emissions. Most closed-path trace-gas analyzers for eddy-covariance measurements have large-volume, multi-pass absorption cells that necessitate high flow rates for ample frequency response, thus requiring high-power sample pumps. Other sampling system components, including rain caps, filters, dryers, and tubing, can also degrade system frequency response. This field trial tested the performance of a closed-path eddy-covariance system for N2O flux measurements with improvements to use less power while maintaining the frequency response. The new system consists of a thermoelectrically cooled tunable diode laser absorption spectrometer configured to measure both N2O and carbon dioxide (CO2. The system features a relatively small, single-pass sample cell (200 mL that provides good frequency response with a lower-powered pump ( ∼  250 W. A new filterless intake removes particulates from the sample air stream with no additional mixing volume that could degrade frequency response. A single-tube dryer removes water vapour from the sample to avoid the need for density or spectroscopic corrections, while maintaining frequency response. This eddy-covariance system was collocated with a previous tunable diode laser absorption spectrometer model to compare N2O and CO2 flux measurements for two full growing seasons (May 2015 to October 2016 in a fertilized cornfield in Southern Ontario, Canada. Both spectrometers were placed outdoors at the base of the sampling tower, demonstrating ruggedness for a range of environmental conditions (minimum to maximum daily temperature range: −26.1 to 31.6 °C. The new system rarely required maintenance. An in situ frequency-response test demonstrated that the cutoff frequency of the new system was better than the old system (3.5 Hz compared to 2.30 Hz and similar to that of a closed

Evaluation of a lower-powered analyzer and sampling system for eddy-covariance measurements of nitrous oxide fluxes

Science.gov (United States)

Brown, Shannon E.; Sargent, Steve; Wagner-Riddle, Claudia

2018-03-01

Nitrous oxide (N2O) fluxes measured using the eddy-covariance method capture the spatial and temporal heterogeneity of N2O emissions. Most closed-path trace-gas analyzers for eddy-covariance measurements have large-volume, multi-pass absorption cells that necessitate high flow rates for ample frequency response, thus requiring high-power sample pumps. Other sampling system components, including rain caps, filters, dryers, and tubing, can also degrade system frequency response. This field trial tested the performance of a closed-path eddy-covariance system for N2O flux measurements with improvements to use less power while maintaining the frequency response. The new system consists of a thermoelectrically cooled tunable diode laser absorption spectrometer configured to measure both N2O and carbon dioxide (CO2). The system features a relatively small, single-pass sample cell (200 mL) that provides good frequency response with a lower-powered pump ( ˜ 250 W). A new filterless intake removes particulates from the sample air stream with no additional mixing volume that could degrade frequency response. A single-tube dryer removes water vapour from the sample to avoid the need for density or spectroscopic corrections, while maintaining frequency response. This eddy-covariance system was collocated with a previous tunable diode laser absorption spectrometer model to compare N2O and CO2 flux measurements for two full growing seasons (May 2015 to October 2016) in a fertilized cornfield in Southern Ontario, Canada. Both spectrometers were placed outdoors at the base of the sampling tower, demonstrating ruggedness for a range of environmental conditions (minimum to maximum daily temperature range: -26.1 to 31.6 °C). The new system rarely required maintenance. An in situ frequency-response test demonstrated that the cutoff frequency of the new system was better than the old system (3.5 Hz compared to 2.30 Hz) and similar to that of a closed-path CO2 eddy-covariance system (4

CO2 and CH4 fluxes in a Spartina salt marsh and brackish Phragmites marsh in Massachusetts

Science.gov (United States)

Tang, J.; Wang, F.; Kroeger, K. D.; Gonneea, M. E.

2017-12-01

Coastal salt marshes play an important role in global and regional carbon cycling. Tidally restricted marshes reduce salinity and provide a habitat suitable for Phragmites invasion. We measured greenhouse gas (GHG) emissions (CO2 and CH4) continuously with the eddy covariance method and biweekly with the static chamber method in a Spartina salt marsh and a Phragmites marsh on Cape Cod, Massachusetts, USA. We did not find significant difference in CO2 fluxes between the two sites, but the CH4 fluxes were much higher in the Phragmites site than the Spartina marsh. Temporally, tidal cycles influence the CO2 and CH4 fluxes in both sites. We found that the salt marsh was a significant carbon sink when CO2 and CH4 fluxes were combined. Restoring tidally restricted marshes will significantly reduce CH4 emissions and provide a strong ecosystem carbon service.

Response of CO2 and H2O fluxes in a mountainous tropical rainforest in equatorial Indonesia to El Niño events

DEFF Research Database (Denmark)

Olchev, A.; Ibrom, Andreas; Panferov, O.

2015-01-01

The possible impact of El Niño–Southern Oscillation (ENSO) events on the main components of CO2 and H2O fluxes in a pristine mountainous tropical rainforest growing in Central Sulawesi in Indonesia is described. The fluxes were continuously measured using the eddy covariance method for the period...

Concurrent CO2 and COS fluxes across major biomes in Europe

Science.gov (United States)

Spielmann, Felix M.; Kitz, Florian; Hammerle, Albin; Gerdel, Katharina; Ibrom, Andreas; Kolle, Olaf; Migliavacca, Mirco; Moreno, Gerardo; Noe, Steffen M.; Wohlfahrt, Georg

2017-04-01

The trace gas carbonyl sulfide (COS) has been proposed as a tracer for canopy gross primary production (GPP), canopy transpiration and stomatal conductance of plant canopies in the last few years. COS enters the plant leaf through the stomata and diffuses through the intercellular space, the cell wall, the plasma membrane and the cytosol like carbon dioxide (CO2). It is then catalyzed by the enzyme carbonic anhydrase in a one-way reaction to hydrogen sulfide and CO2. This one-way flux into the leaf makes COS a promising tracer for the GPP. However, this approach assumes that the ratio of the deposition velocities between COS and CO2 is constant, which must be determined in field experiments covering a wide variety of ecosystems. The overarching objective of this study was to quantify the relationship between the ecosystem-scale exchange of COS and CO2 and thus, to test for the potential of COS to be used as a universal tracer for the plant canopy CO2 exchange. Between spring 2015 and summer 2016 we set up our quantum cascade laser at different field sites across Europe. These sites included a managed temperate mountain grassland (AUT), a savanna (ESP), a temperate beech forest (DEN) and a hemiboreal forest (EST). On each of these sites, we conducted ecosystem scale eddy covariance and soil chamber measurements. Since the soil COS flux contribution, especially in grass dominated ecosystems, could not be neglected, we had to derive the actual canopy COS fluxes for all the measurement sites. Using these fluxes we compared the ecosystem relative uptake (ERU) of the sites and searched for factors affecting its variability. We then used the influential factors to scale the ERU to be comparable under different field sites and conditions. Furthermore we also calculated the GPP using conventional CO2 flux partitioning and compared the results with the approach of using the leaf relative uptake.

The role of vegetation in the CO2 flux from a tropical urban neighbourhood

Science.gov (United States)

Velasco, E.; Roth, M.; Tan, S. H.; Quak, M.; Nabarro, S. D. A.; Norford, L.

2013-03-01

Urban surfaces are usually net sources of CO2. Vegetation can potentially have an important role in reducing the CO2 emitted by anthropogenic activities in cities, particularly when vegetation is extensive and/or evergreen. Negative daytime CO2 fluxes, for example have been observed during the growing season at suburban sites characterized by abundant vegetation and low population density. A direct and accurate estimation of carbon uptake by urban vegetation is difficult due to the particular characteristics of the urban ecosystem and high variability in tree distribution and species. Here, we investigate the role of urban vegetation in the CO2 flux from a residential neighbourhood in Singapore using two different approaches. CO2 fluxes measured directly by eddy covariance are compared with emissions estimated from emissions factors and activity data. The latter includes contributions from vehicular traffic, household combustion, soil respiration and human breathing. The difference between estimated emissions and measured fluxes should approximate the biogenic flux. In addition, a tree survey was conducted to estimate the annual CO2 sequestration using allometric equations and an alternative model of the metabolic theory of ecology for tropical forests. Palm trees, banana plants and turfgrass were also included in the survey with their annual CO2 uptake obtained from published growth rates. Both approaches agree within 2% and suggest that vegetation captures 8% of the total emitted CO2 in the residential neighbourhood studied. A net uptake of 1.4 ton km-2 day-1 (510 ton km-2 yr-1 ) was estimated from the difference between the daily CO2 uptake by photosynthesis (3.95 ton km-2 ) and release by respiration (2.55 ton km-2). The study shows the importance of urban vegetation at the local scale for climate change mitigation in the tropics.

Modeling light use efficiency in a subtropical mangrove forest equipped with CO2 eddy covariance

Directory of Open Access Journals (Sweden)

J. G. Barr

2013-03-01

Full Text Available Despite the importance of mangrove ecosystems in the global carbon budget, the relationships between environmental drivers and carbon dynamics in these forests remain poorly understood. This limited understanding is partly a result of the challenges associated with in situ flux studies. Tower-based CO2 eddy covariance (EC systems are installed in only a few mangrove forests worldwide, and the longest EC record from the Florida Everglades contains less than 9 years of observations. A primary goal of the present study was to develop a methodology to estimate canopy-scale photosynthetic light use efficiency in this forest. These tower-based observations represent a basis for associating CO2 fluxes with canopy light use properties, and thus provide the means for utilizing satellite-based reflectance data for larger scale investigations. We present a model for mangrove canopy light use efficiency utilizing the enhanced green vegetation index (EVI derived from the Moderate Resolution Imaging Spectroradiometer (MODIS that is capable of predicting changes in mangrove forest CO2 fluxes caused by a hurricane disturbance and changes in regional environmental conditions, including temperature and salinity. Model parameters are solved for in a Bayesian framework. The model structure requires estimates of ecosystem respiration (RE, and we present the first ever tower-based estimates of mangrove forest RE derived from nighttime CO2 fluxes. Our investigation is also the first to show the effects of salinity on mangrove forest CO2 uptake, which declines 5% per each 10 parts per thousand (ppt increase in salinity. Light use efficiency in this forest declines with increasing daily photosynthetic active radiation, which is an important departure from the assumption of constant light use efficiency typically applied in satellite-driven models. The model developed here provides a framework for estimating CO2 uptake by these forests from reflectance data and

CO2 flux from Javanese mud volcanism.

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Queißer, M; Burton, M R; Arzilli, F; Chiarugi, A; Marliyani, G I; Anggara, F; Harijoko, A

2017-06-01

Studying the quantity and origin of CO 2 emitted by back-arc mud volcanoes is critical to correctly model fluid-dynamical, thermodynamical, and geochemical processes that drive their activity and to constrain their role in the global geochemical carbon cycle. We measured CO 2 fluxes of the Bledug Kuwu mud volcano on the Kendeng Fold and thrust belt in the back arc of Central Java, Indonesia, using scanning remote sensing absorption spectroscopy. The data show that the expelled gas is rich in CO 2 with a volume fraction of at least 16 vol %. A lower limit CO 2 flux of 1.4 kg s -1 (117 t d -1 ) was determined, in line with the CO 2 flux from the Javanese mud volcano LUSI. Extrapolating these results to mud volcanism from the whole of Java suggests an order of magnitude total CO 2 flux of 3 kt d -1 , comparable with the expected back-arc efflux of magmatic CO 2 . After discussing geochemical, geological, and geophysical evidence we conclude that the source of CO 2 observed at Bledug Kuwu is likely a mixture of thermogenic, biogenic, and magmatic CO 2 , with faulting controlling potential pathways for magmatic fluids. This study further demonstrates the merit of man-portable active remote sensing instruments for probing natural gas releases, enabling bottom-up quantification of CO 2 fluxes.

Retrieval of average CO2 fluxes by combining in situ CO2 measurements and backscatter lidar information

Science.gov (United States)

Gibert, Fabien; Schmidt, Martina; Cuesta, Juan; Ciais, Philippe; Ramonet, Michel; Xueref, IrèNe; Larmanou, Eric; Flamant, Pierre Henri

2007-05-01

The present paper deals with a boundary layer budgeting method which makes use of observations from various in situ and remote sensing instruments to infer regional average net ecosystem exchange (NEE) of CO2. Measurements of CO2 within and above the atmospheric boundary layer (ABL) by in situ sensors, in conjunction with a precise knowledge of the change in ABL height by lidar and radiosoundings, enable to infer diurnal and seasonal NEE variations. Near-ground in situ CO measurements are used to discriminate natural and anthropogenic contributions of CO2 diurnal variations in the ABL. The method yields mean NEE that amounts to 5 μmol m-2 s-1 during the night and -20 μmol m-2 s-1 in the middle of the day between May and July. A good agreement is found with the expected NEE accounting for a mixed wheat field and forest area during winter season, representative of the mesoscale ecosystems in the Paris area according to the trajectory of an air column crossing the landscape. Daytime NEE is seen to follow the vegetation growth and the change in the ratio diffuse/direct radiation. The CO2 vertical mixing flux during the rise of the atmospheric boundary layer is also estimated and seems to be the main cause of the large decrease of CO2 mixing ratio in the morning. The outcomes on CO2 flux estimate are compared to eddy-covariance measurements on a barley field. The importance of various sources of error and uncertainty on the retrieval is discussed. These errors are estimated to be less than 15%; the main error resulted from anthropogenic emissions.

Regional inversion of CO2 ecosystem fluxes from atmospheric measurements. Reliability of the uncertainty estimates

Energy Technology Data Exchange (ETDEWEB)

Broquet, G.; Chevallier, F.; Breon, F.M.; Yver, C.; Ciais, P.; Ramonet, M.; Schmidt, M. [Laboratoire des Sciences du Climat et de l' Environnement, CEA-CNRS-UVSQ, UMR8212, IPSL, Gif-sur-Yvette (France); Alemanno, M. [Servizio Meteorologico dell' Aeronautica Militare Italiana, Centro Aeronautica Militare di Montagna, Monte Cimone/Sestola (Italy); Apadula, F. [Research on Energy Systems, RSE, Environment and Sustainable Development Department, Milano (Italy); Hammer, S. [Universitaet Heidelberg, Institut fuer Umweltphysik, Heidelberg (Germany); Haszpra, L. [Hungarian Meteorological Service, Budapest (Hungary); Meinhardt, F. [Federal Environmental Agency, Kirchzarten (Germany); Necki, J. [AGH University of Science and Technology, Krakow (Poland); Piacentino, S. [ENEA, Laboratory for Earth Observations and Analyses, Palermo (Italy); Thompson, R.L. [Max Planck Institute for Biogeochemistry, Jena (Germany); Vermeulen, A.T. [Energy research Centre of the Netherlands ECN, EEE-EA, Petten (Netherlands)

2013-07-01

The Bayesian framework of CO2 flux inversions permits estimates of the retrieved flux uncertainties. Here, the reliability of these theoretical estimates is studied through a comparison against the misfits between the inverted fluxes and independent measurements of the CO2 Net Ecosystem Exchange (NEE) made by the eddy covariance technique at local (few hectares) scale. Regional inversions at 0.5{sup 0} resolution are applied for the western European domain where {approx}50 eddy covariance sites are operated. These inversions are conducted for the period 2002-2007. They use a mesoscale atmospheric transport model, a prior estimate of the NEE from a terrestrial ecosystem model and rely on the variational assimilation of in situ continuous measurements of CO2 atmospheric mole fractions. Averaged over monthly periods and over the whole domain, the misfits are in good agreement with the theoretical uncertainties for prior and inverted NEE, and pass the chi-square test for the variance at the 30% and 5% significance levels respectively, despite the scale mismatch and the independence between the prior (respectively inverted) NEE and the flux measurements. The theoretical uncertainty reduction for the monthly NEE at the measurement sites is 53% while the inversion decreases the standard deviation of the misfits by 38 %. These results build confidence in the NEE estimates at the European/monthly scales and in their theoretical uncertainty from the regional inverse modelling system. However, the uncertainties at the monthly (respectively annual) scale remain larger than the amplitude of the inter-annual variability of monthly (respectively annual) fluxes, so that this study does not engender confidence in the inter-annual variations. The uncertainties at the monthly scale are significantly smaller than the seasonal variations. The seasonal cycle of the inverted fluxes is thus reliable. In particular, the CO2 sink period over the European continent likely ends later than

Atmospheric inversion of the surface CO2 flux with 13CO2 constraint

Science.gov (United States)

Chen, J. M.; Mo, G.; Deng, F.

2013-10-01

Observations of 13CO2 at 73 sites compiled in the GLOBALVIEW database are used for an additional constraint in a global atmospheric inversion of the surface CO2 flux using CO2 observations at 210 sites for the 2002-2004 period for 39 land regions and 11 ocean regions. This constraint is implemented using the 13CO2/CO2 flux ratio modeled with a terrestrial ecosystem model and an ocean model. These models simulate 13CO2 discrimination rates of terrestrial photosynthesis and respiration and ocean-atmosphere diffusion processes. In both models, the 13CO2 disequilibrium between fluxes to and from the atmosphere is considered due to the historical change in atmospheric 13CO2 concentration. For the 2002-2004 period, the 13CO2 constraint on the inversion increases the total land carbon sink from 3.40 to 3.70 Pg C yr-1 and decreases the total oceanic carbon sink from 1.48 to 1.12 Pg C yr-1. The largest changes occur in tropical areas: a considerable decrease in the carbon source in the Amazon forest, and this decrease is mostly compensated by increases in the ocean region immediately west of the Amazon and the southeast Asian land region. Our further investigation through different treatments of the 13CO2/CO2 flux ratio used in the inversion suggests that variable spatial distributions of the 13CO2 isotopic discrimination rate simulated by the models over land and ocean have considerable impacts on the spatial distribution of the inverted CO2 flux over land and the inversion results are not sensitive to errors in the estimated disequilibria over land and ocean.

Regional variability of grassland CO2 fluxes in Tyrol/Austria

Science.gov (United States)

Irschick, Christoph; Hammerle, Albin; Haslwanter, Alois; Wohlfahrt, Georg

2010-05-01

The FLUXNET project [1] aims at quantifying the magnitude and controls on the CO2, H2O and energy exchange of terrestrial ecosystems. Ideally, the various biomes of the Earth would be sampled in proportion to their spatial extent - in reality, however, study site selection is usually based on other (more practical) criteria so that a bias exists towards certain biomes and ecosystem types. This may be problematic because FLUXNET data are used to calibrate/parameterize models at various scales - if certain ecosystems are poorly replicated this may bias model predictions. Here we present data from a project in Tyrol/Austria where we have been investigating the CO2, H2O and energy exchange of five grassland sites during 2005-2007. The five permanent grassland sites were exposed to similar climate, but differed slightly in management. In a FLUXNET style approach, any of these sites might have been selected for making long-term flux measurements - the aim of this project was to examine the representativeness of these sites and, if evident, elucidate the causes for and controls on differences between sites. To this end we conducted continuous eddy covariance flux measurements at one (anchor) site [2, 3], and episodic, month long flux measurements at the four additional sites using a roving eddy covariance tower. These data were complemented by measurements of environmental drivers, the amount of above ground phytomass and basic data on vegetation and soil type, as well as management. Data are subject to a rigorous statistical analysis in order to quantify significant differences in the CO2, H2O and energy exchange between the sites and to identify the factors which are responsible for these differences. In the present contribution we report results on CO2 fluxes. Our major findings are that (i) site-identity of the surveyed grassland ecosystems was a significant factor for the net ecosystem CO2 exchange (NEE), somewhat less for gross primary production (GPP) and not for

Global CO2 fluxes estimated from GOSAT retrievals of total column CO2

Directory of Open Access Journals (Sweden)

S. Basu

2013-09-01

Full Text Available We present one of the first estimates of the global distribution of CO2 surface fluxes using total column CO2 measurements retrieved by the SRON-KIT RemoTeC algorithm from the Greenhouse gases Observing SATellite (GOSAT. We derive optimized fluxes from June 2009 to December 2010. We estimate fluxes from surface CO2 measurements to use as baselines for comparing GOSAT data-derived fluxes. Assimilating only GOSAT data, we can reproduce the observed CO2 time series at surface and TCCON sites in the tropics and the northern extra-tropics. In contrast, in the southern extra-tropics GOSAT XCO2 leads to enhanced seasonal cycle amplitudes compared to independent measurements, and we identify it as the result of a land–sea bias in our GOSAT XCO2 retrievals. A bias correction in the form of a global offset between GOSAT land and sea pixels in a joint inversion of satellite and surface measurements of CO2 yields plausible global flux estimates which are more tightly constrained than in an inversion using surface CO2 data alone. We show that assimilating the bias-corrected GOSAT data on top of surface CO2 data (a reduces the estimated global land sink of CO2, and (b shifts the terrestrial net uptake of carbon from the tropics to the extra-tropics. It is concluded that while GOSAT total column CO2 provide useful constraints for source–sink inversions, small spatiotemporal biases – beyond what can be detected using current validation techniques – have serious consequences for optimized fluxes, even aggregated over continental scales.

Comparison of regional and ecosystem CO{sub 2} fluxes

Energy Technology Data Exchange (ETDEWEB)

Gryning, S. E. (Wind Energy Department, Risoe National Laboratory for Sustainable Energy, Technical Univ. of Denmark, Roskilde (Denmark)); Soegaard, H. (Institute of Geography and Geology, University of Copenhagen, Copenhagen (Denmark)); Batchvarova, E. (National Institute of Meteorology and Hydrology, Bulgarian Academy of Sciences, Sofia (Bulgaria))

2009-07-01

A budget method to derive the regional surface flux of CO{sub 2} from the evolution of the boundary layer is presented and applied. The necessary input for the method can be deduced from a combination of vertical profile measurements of CO{sub 2} concentrations by i.e. an airplane, successive radio-soundings and standard measurements of the CO{sub 2} concentration near the ground. The method was used to derive the regional flux of CO{sub 2} over an agricultural site at Zealand in Denmark during an experiment on 12-13 June 2006. The regional fluxes of CO{sub 2} represent a combination of agricultural and forest surface conditions. It was found that the regional flux of CO{sub 2} in broad terms follows the behavior of the flux of CO{sub 2} at the agricultural (grassland) and the deciduous forest station. The regional flux is comparable not only in size but also in the diurnal (daytime) cycle of CO{sub 2} fluxes at the two stations. (orig.)

Annual balances of CH4 and N2O from a managed fen meadow using eddy covariance flux measurements

International Nuclear Information System (INIS)

Schrier-Uijl, A.P.; Veenendaal, E.M.; Kroon, P.S.; Hensen, A.; Jonker, H.J.J.

2010-10-01

Annual terrestrial balances of methane (CH4) and nitrous oxide (N2O) are presented for a managed fen meadow in the Netherlands for 2006, 2007 and 2008, using eddy covariance (EC) flux measurements. Annual emissions derived from different methods are compared. The most accurate annual CH4 flux is achieved by gap filling EC fluxes with an empirical multivariate regression model, with soil temperature and mean wind velocity as driving variables. This model explains about 60% of the variability in observed daily CH4 fluxes. Annual N2O emissions can be separated into background emissions and event emissions due to fertilization. The background emission is estimated using a multivariate regression model also based on EC flux data, with soil temperature and mean wind velocity as driving variables. The event emissions are estimated using emission factors. The minimum direct emission factor is derived for six fertilization events by subtracting the background emission, and the IPCC default emission factor of 1% is used for the other events. In addition, the maximum direct emission factors are determined for the six events without subtracting the background emission. The average direct emission factor ranges from 1.2 to 2.8%, which is larger than the IPCC default value. Finally, the total terrestrial greenhouse gas balance is estimated at 16 Mg ha -1 year -1 in CO2-equivalents with contributions of 30, 25 and 45% by CO2, CH4 and N2O, respectively.

LOW-POWER SOLUTION FOR EDDY COVARIANCE MEASUREMENTS OF METHANE FLUX

Science.gov (United States)

Anderson, T.; Burba, G. G.; Komissarov, A.; McDermitt, D. K.; Xu, L.; Zona, D.; Oechel, W. C.; Schedlbauer, J. L.; Oberbauer, S. F.; Riensche, B.; Allyn, D.

2009-12-01

Open-path analyzers offer a number of advantages for measuring methane fluxes, including undisturbed in-situ flux measurements, spatial integration using the Eddy Covariance approach, zero frequency response errors due to tube attenuation, confident water and thermal density terms from co-located fast measurements of water and sonic temperature, and possibility of remote and mobile solar-powered or small-generator-powered deployments due to lower power demands in the absence of a pump. The LI-7700 open-path methane analyzer is a VCSEL (vertical-cavity surface-emitting laser)-based instrument. It employs an open Herriott cell and measures levels of methane with RMS noise below 5 ppb at 10 Hz sampling in controlled laboratory conditions. The power consumption of the stand-alone LI-7700 in steady-state is about 8W, so it can be deployed in any methane-generating location of interest on a portable or mobile solar-powered tower, and it does not have to have grid power or permanent industrial generator. Eddy Covariance measurements of methane flux using the LI-7700 open-path methane analyzer were conducted in 2006-2009 in five ecosystems with contrasting weather and moisture conditions: (1) sawgrass wetland in the Florida Everglades; (2) coastal wetlands in an Arctic tundra; and (3) pacific mangroves in Mexico; (4) maize field and (5) ryegrass field in Nebraska. Methane co-spectra behaved in a manner similar to that of the co-spectra of carbon dioxide, water vapor, and air temperature, demonstrating that the LI-7700 adequately measured fluctuations in methane concentration across the whole spectrum of frequencies contributing to vertical atmospheric turbulent transport at the experimental sites. All co-spectra also closely followed the Kaimal model, and demonstrated good agreement with another methane co-spectrum obtained with a TDLS (Tunable Diode Laser Spectroscope; Unisearch Associates, Inc.) over a peatland. Overall, hourly methane fluxes ranged from near-zero at

N2O fluxes over a corn field from an open-path, laser-based eddy covariance system and static chambers

Science.gov (United States)

Tao, L.; Pan, D.; Gelfand, I.; Abraha, M.; Moyer, R.; Poe, A.; Sun, K.; Robertson, P.; Zondlo, M. A.

2015-12-01

Nitrous oxide (N2O) is important greenhouse and ozone-depleting gase. Although many efforts have been paid to N2O emissions, the spatial and temporal variability of N2O emissions still subject to large uncertainty. Application of the eddy covariance method for N2O emissions research would allow continuous ecosystem level flux measurements. The caveat, however, is need for high precision and high frequency measurements in field. In this study, an open-path, quantum cascade-laser-based eddy covariance N2O sensor has been deployed nearly continuously since May 2015 over a corn field at the W.K. Kellogg Biological Station site in SW Michigan. The field precision of the N2O sensor was assessed to be 0.1 ppbv at 10 Hz, and the total consumption was ~ 40 W, allowing the system to be powered solely by solar panels. The stability of the sensor under different temperature and humidity was tested within an environmental chamber. Spectroscopic experiments and cospectra analyses were carried out to study specific corrections associated with the sensor for eddy covariance techniques, including the line broadening effect due to water vapor and high frequency flux attenuation owning to sample path averaging. Ogive analyses indicated that the high-frequency N2O flux loss due to various damping effects was comparable to those of the CO2 flux. The detection limit of flux was estimated to be 0.3 ng N s-1 m-2 with a flux averaging interval of 30 minutes. The results from the EC system were also compared with ground measurements by standard static chambers (SC). Overall, more than 150 individual chamber measurements were taken within the footprint of the EC system. We found good correlation between the EC and SC methods given the spatiotemporal differences between the two techniques (R2 = 0.75). Both methods detected increased emissions during afternoon as compared to morning and night hours. Differences between EC and SC were also studied by investigating spatial variability with a

A Spatial-Temporal Comparison of Lake Mendota CO2 Fluxes and Collection Methods

Science.gov (United States)

Baldocchi, A. K.; Reed, D. E.; Desai, A. R.; Loken, L. C.; Schramm, P.; Stanley, E. H.

2017-12-01

Monitoring of carbon fluxes at the lake/atmosphere interface can help us determine baselines from which to understand responses in both space and time that may result from our warming climate or increasing nutrient inputs. Since recent research has shown lakes to be hotspots of global carbon cycling, it is important to quantify carbon sink and source dynamics as well as to verify observations between multiple methods in the context of long-term data collection efforts. Here we evaluate a new method for measuring space and time variation in CO2 fluxes based on novel speedboat-based collection method of aquatic greenhouse gas concentrations and a flux computation and interpolation algorithm. Two-hundred and forty-nine consecutive days of spatial flux maps over the 2016 open ice period were compared to ongoing eddy covariance tower flux measurements on the shore of Lake Mendota, Wisconsin US using a flux footprint analysis. Spatial and temporal alignments of the fluxes from these two observational datasets revealed both similar trends from daily to seasonal timescales as well as biases between methods. For example, throughout the Spring carbon fluxes showed strong correlation although off by an order of magnitude. Isolating physical patterns of agreement between the two methods of the lake/atmosphere CO2 fluxes allows us to pinpoint where biology and physical drivers contribute to the global carbon cycle and help improve modelling of lakes and utilize lakes as leading indicators of climate change.

Net ecosystem exchange of CO2 and H2O fluxes from irrigated grain sorghum and maize in the Texas High Plains

Science.gov (United States)

Net ecosystem exchange (NEE) of carbon dioxide (CO2) and water vapor (H2O) fluxes from irrigated grain sorghum (Sorghum bicolor L. Moench) and maize (Zea mays L.) fields in the Texas High Plains were quantified using the eddy covariance (EC) technique during 2014-2016 growing seasons and examined in...

Air-sea fluxes of CO2 and CH4 from the Penlee Point Atmospheric Observatory on the south-west coast of the UK

Science.gov (United States)

Yang, Mingxi; Bell, Thomas G.; Hopkins, Frances E.; Kitidis, Vassilis; Cazenave, Pierre W.; Nightingale, Philip D.; Yelland, Margaret J.; Pascal, Robin W.; Prytherch, John; Brooks, Ian M.; Smyth, Timothy J.

2016-05-01

We present air-sea fluxes of carbon dioxide (CO2), methane (CH4), momentum, and sensible heat measured by the eddy covariance method from the recently established Penlee Point Atmospheric Observatory (PPAO) on the south-west coast of the United Kingdom. Measurements from the south-westerly direction (open water sector) were made at three different sampling heights (approximately 15, 18, and 27 m above mean sea level, a.m.s.l.), each from a different period during 2014-2015. At sampling heights ≥ 18 m a.m.s.l., measured fluxes of momentum and sensible heat demonstrate reasonable ( ≤ ±20 % in the mean) agreement with transfer rates over the open ocean. This confirms the suitability of PPAO for air-sea exchange measurements in shelf regions. Covariance air-sea CO2 fluxes demonstrate high temporal variability. Air-to-sea transport of CO2 declined from spring to summer in both years, coinciding with the breakdown of the spring phytoplankton bloom. We report, to the best of our knowledge, the first successful eddy covariance measurements of CH4 emissions from a marine environment. Higher sea-to-air CH4 fluxes were observed during rising tides (20 ± 3; 38 ± 3; 29 ± 6 µmole m-2 d-1 at 15, 18, 27 m a.m.s.l.) than during falling tides (14 ± 2; 22 ± 2; 21 ± 5 µmole m-2 d-1), consistent with an elevated CH4 source from an estuarine outflow driven by local tidal circulation. These fluxes are a few times higher than the predicted CH4 emissions over the open ocean and are significantly lower than estimates from other aquatic CH4 hotspots (e.g. polar regions, freshwater). Finally, we found the detection limit of the air-sea CH4 flux by eddy covariance to be 20 µmole m-2 d-1 over hourly timescales (4 µmole m-2 d-1 over 24 h).

Assessing the net effect of long-term drainage on a permafrost ecosystem through year-round eddy-covariance flux measurements

Science.gov (United States)

Kittler, F.; Heimann, M.; Goeckede, M.; Zimov, S. A.; Zimov, N.

2014-12-01

Permafrost regions in the Northern high latitudes play a key role in the carbon budget of the earth system because of their massive carbon reservoir and the uncertain feedback processes with future climate change. For an improved understanding of mechanisms and drivers dominating permafrost carbon cycling, more observations in high-latitude regions are needed. Particularly the contribution of wintertime fluxes to the annual carbon budget and the impact of disturbances on biogeochemical and biogeophysical ecosystem properties, and the resulting modification of the carbon cycle, have rarely been studied to date. In summer of 2013, we established a new eddy-covariance station for continuous, year-round monitoring of carbon fluxes and their environmental drivers near Cherskii in Northeast Siberia (68.75°N, 161.33°E). Parts of the observation area have been disturbed by drainage since 2004, altering the soil water conditions in a way that is expected for degrading ice-rich permafrost under a warming climate. With two eddy-covariance towers running in parallel over the disturbed (drained) area and a reference area nearby, respectively, we can directly infer the disturbance effect on the carbon cycle budgets and the dominating biogeochemical mechanisms. This study presents findings based on 16 months of continuous eddy-covariance CO2 flux measurements (July 2013 - October 2014) for both observation areas. At both towers, we observed systematic, non-zero flux contributions outside the growing seasons that significantly altered annual CO2 budgets. A direct comparison of fluxes between the two disturbance regimes indicates a net reduction of the sink strength for CO2 in the disturbed area during the growing season, mostly caused by reduced CO2 uptake with low water levels in late summer. Moreover, shifts in soil temperatures and snow cover caused by reduced soil water levels result in lower net CO2 emissions during the winter at the drained area, which is partly

Comparison of chamber and eddy covariance-based CO2 and CH4 emission estimates in a heterogeneous grass ecosystem on peat

International Nuclear Information System (INIS)

Schrier-Uijl, A.P.; Berendse, F.; Veenendaal, E.M.; Kroon, P.S.; Hensen, A.; Leffelaar, P.A.

2010-08-01

Fluxes of methane (CH4) and carbon dioxide (CO2) estimated by empirical models based on small-scale chamber measurements were compared to large-scale eddy covariance (EC) measurements for CH4 and to a combination of EC measurements and EC-based models for CO2. The experimental area was a flat peat meadow in the Netherlands with heterogeneous source strengths for both greenhouse gases. Two scenarios were used to assess the importance of stratifying the landscape into landscape elements before up-scaling the fluxes measured by chambers to landscape scale: one took the main landscape elements into account (field, ditch edge ditch), the other took only the field into account. Non-linear regression models were used to up-scale the chamber measurements to field emission estimates. EC CO2 respiration consisted of measured night time EC fluxes and modeled day time fluxes using the Arrhenius model. EC CH4 flux estimate was based on daily averages and the remaining data gaps were filled by linear interpolation. The EC and chamber-based estimates agreed well when the three landscape elements were taken into account with 16.5% and 13.0% difference for CO2 respiration and CH4, respectively. However, both methods differed 31.0% and 55.1% for CO2 respiration and CH4 when only field emissions were taken into account when up-scaling chamber measurements to landscape scale. This emphasizes the importance of stratifying the landscape into landscape elements. The conclusion is that small-scale chamber measurements can be used to estimate fluxes of CO2 and CH4 at landscape scale if fluxes are scaled by different landscape elements.

Spatial and temporal variability of land CO{sub 2} fluxes estimated with remote sensing and analysis data over western Eurasia

Energy Technology Data Exchange (ETDEWEB)

Lafont, S.; Dedieu, G. [CESBIO (CNRS/CNES/UPS), Toulouse (France); Kergoat, L. [LET (CNRS/UPS), Toulouse (France); Chevillard, A. [CEA Saclay, Gif-sur-Yvette (France). Laboratoire des Sciences du Climat et de l' Environnement; Karstens, U. [MPI-MET, Hamburg (Germany); Kolle, O. [Max-Planck Inst. for Biogeochemistry, Jena (Germany)

2002-11-01

The Eurosiberian Carbonflux project was designed to address the feasibility of inferring the regional carbon balance over Europe and Siberia from a hierarchy of models and atmospheric CO{sub 2} measurements over the continent. Such atmospheric CO{sub 2} concentrations result from the combination of connective boundary layer dynamics, synoptic events, large-scale transport of CO{sub 2}, and regional surface fluxes and depend on the variability of these processes in time and space. In this paper we investigate the spatial and temporal variability of the land surface CO{sub 2} fluxes derived from the TURC model. This productivity model is driven by satellite NDVI and forced by ECMWF or REMO meteorology. We first present an analysis of recent CO{sub 2} flux measurements over temperate and boreal forests, which are used to update the TURC model. A strong linear relationship has been found between maximum hourly CO{sub 2} fluxes and the mean annual air temperature, showing that boreal biomes have a lower photosynthetic capacity than temperate ones. Then, model input consistency and simulated CO{sub 2} flux accuracy are evaluated against local measurements from two sites in Russia. Finally, the spatial and temporal patterns of the daily CO{sub 2} fluxes over Eurasia are analysed. We show that, during the growing season (spring and summer), the daily CO{sub 2} fluxes display characteristic spatial patterns of positive and negative fluxes at the synoptic scale. These patterns are found to correspond to cloudy areas (areas with low incoming radiation) and to follow the motion of cloud cover areas over the whole domain. As a consequence, we argue that co-variations of surface CO{sub 2} fluxes and atmospheric transport at the synoptic scale may impact CO{sub 2} concentrations over continents and need to be investigated.

Expanding Spatial and Temporal Coverage of Arctic CH4 and CO2 Fluxes

Science.gov (United States)

Murphy, P.; Oechel, W. C.; Moreaux, V.; Losacco, S.; Zona, D.

2013-12-01

Carbon storage and exchange in Arctic ecosystems is the subject of intensive study focused on determining rates, controls, and mechanisms of CH4 and CO2 fluxes. The Arctic contains more than 1 Gt of Carbon in the upper meter of soil, both in the active layer and permafrost (Schuur et al., 2008; Tarnocai et al., 2009). However, the annual pattern and controls on the release of CH4 is inadequately understood in Arctic tundra ecosystems. Annual methane budgets are poorly understood, and very few studies measure fluxes through the freeze-up cycle during autumn months (Mastepanov et al., 2008; Mastepanov et al., 2010; Sturtevant et al., 2012). There is no known, relatively continuous, CH4 flux record for the Arctic. Clearly, the datasets that currently exist for budget calculations and model parameterization and verification are inadequate. This is likely due to the difficult nature of flux measurements in the Arctic. In September 2012, we initiated a research project towards continuous methane flux measurements along a latitudinal transect in Northern Alaska. The eddy-covariance (EC) technique is challenging in such extreme weather conditions due to the effects of ice formation and precipitation on instrumentation, including gas analyzers and sonic anemometers. The challenge is greater in remote areas of the Arctic, when low power availability and limited communication can lead to delays in data retrieval or data loss. For these reasons, a combination of open- and closed-path gas analyzers, and several sonic anemometers (including one with heating), have been installed on EC towers to allow for cross-comparison and cross-referencing of calculated fluxes. Newer instruments for fast CH4 flux determination include: the Los Gatos Research Fast Greenhouse Gas Analyzer and the Li-Cor LI-7700. We also included the self-heated Metek Class-A uSonic-3 Anemometer as a new instrument. Previously existing instruments used for comparison include the Li-Cor LI-7500; Li-Cor LI-7200

Soil surface CO2 fluxes on the Konza Prairie

Science.gov (United States)

Norman, J. M.; Garcia, R.; Verma, Shoshi B.

1990-01-01

The utilization of a soil chamber to measure fluxes of soil-surface CO2 fluxes is described in terms of equipment, analytical methods, and estimate quality. A soil chamber attached to a gas-exchange system measures the fluxes every 5-15 min, and the data are compared to measurements of the CO2 fluxes from the canopy and from the soil + canopy. The soil chamber yields good measurements when operated in a closed system that is ported to the free atmosphere, and the CO2 flux is found to have a diurnal component.

Estimating surface fluxes using eddy covariance and numerical ogive optimization

DEFF Research Database (Denmark)

Sievers, J.; Papakyriakou, T.; Larsen, Søren Ejling

2015-01-01

Estimating representative surface fluxes using eddy covariance leads invariably to questions concerning inclusion or exclusion of low-frequency flux contributions. For studies where fluxes are linked to local physical parameters and up-scaled through numerical modelling efforts, low-frequency con......Estimating representative surface fluxes using eddy covariance leads invariably to questions concerning inclusion or exclusion of low-frequency flux contributions. For studies where fluxes are linked to local physical parameters and up-scaled through numerical modelling efforts, low...

Static Vented Chamber and Eddy Covariance Methane Flux Comparisons in Mid-South US Rice

Science.gov (United States)

Reba, M. L.; Fong, B.; Adviento-Borbe, A.; Runkle, B.; Suvocarev, K.; Rival, I.

2017-12-01

Rice cultivation contributes higher amounts of GHG emissions (CO2 and CH4) due to flooded field conditions. A comparison between eddy covariance and static vented flux chamber measurement techniques is presented. Rice GHG emissions originating from plot level chambers may not accurately describe the aggregate effects of all the soil and micrometeorological variations across a production field. Eddy covariance (EC) is a direct, integrated field measurement of field scale trace gases. Flux measurements were collected in NE Arkansas production size rice fields (16 ha, 40 ac) during the 2015 and 2016 production seasons (June-August) in continuous flood (CF) irrigation. The study objectives included quantifying the difference between chamber and EC measurements, and categorizing flux behavior to growth stage and field history. EC daily average emissions correlated with chamber measurements (R2=0.27-0.54) more than average from 09:00-12:00 which encompassed chamber measurement times (R2=0.23-0.32). Maximum methane emissions occurred in the late afternoon from 14:00-18:00 which corresponded with maximum soil heat flux and air temperature. The total emissions from the study fields ranged from 27-117 kg CH4-C ha-1 season-1. The emission profile was lower in 2015, most likely due to higher rainfall and cooler temperatures during the growing season compared to 2016. These findings improve our understanding of GHG emissions at the field scale under typical production practices and validity of chamber and EC flux measurement techniques.

Air–sea fluxes of CO2 and CH4 from the Penlee Point Atmospheric Observatory on the south-west coast of the UK

Directory of Open Access Journals (Sweden)

M. Yang

2016-05-01

Full Text Available We present air–sea fluxes of carbon dioxide (CO2, methane (CH4, momentum, and sensible heat measured by the eddy covariance method from the recently established Penlee Point Atmospheric Observatory (PPAO on the south-west coast of the United Kingdom. Measurements from the south-westerly direction (open water sector were made at three different sampling heights (approximately 15, 18, and 27 m above mean sea level, a.m.s.l., each from a different period during 2014–2015. At sampling heights  ≥  18 m a.m.s.l., measured fluxes of momentum and sensible heat demonstrate reasonable ( ≤  ±20 % in the mean agreement with transfer rates over the open ocean. This confirms the suitability of PPAO for air–sea exchange measurements in shelf regions. Covariance air–sea CO2 fluxes demonstrate high temporal variability. Air-to-sea transport of CO2 declined from spring to summer in both years, coinciding with the breakdown of the spring phytoplankton bloom. We report, to the best of our knowledge, the first successful eddy covariance measurements of CH4 emissions from a marine environment. Higher sea-to-air CH4 fluxes were observed during rising tides (20 ± 3; 38 ± 3; 29 ± 6 µmole m−2 d−1 at 15, 18, 27 m a.m.s.l. than during falling tides (14 ± 2; 22 ± 2; 21 ± 5 µmole m−2 d−1, consistent with an elevated CH4 source from an estuarine outflow driven by local tidal circulation. These fluxes are a few times higher than the predicted CH4 emissions over the open ocean and are significantly lower than estimates from other aquatic CH4 hotspots (e.g. polar regions, freshwater. Finally, we found the detection limit of the air–sea CH4 flux by eddy covariance to be 20 µmole m−2 d−1 over hourly timescales (4 µmole m−2 d−1 over 24 h.

Atmospheric CO2 inversions on the mesoscale using data-driven prior uncertainties: quantification of the European terrestrial CO2 fluxes

Science.gov (United States)

Kountouris, Panagiotis; Gerbig, Christoph; Rödenbeck, Christian; Karstens, Ute; Koch, Thomas F.; Heimann, Martin

2018-03-01

Optimized biogenic carbon fluxes for Europe were estimated from high-resolution regional-scale inversions, utilizing atmospheric CO2 measurements at 16 stations for the year 2007. Additional sensitivity tests with different data-driven error structures were performed. As the atmospheric network is rather sparse and consequently contains large spatial gaps, we use a priori biospheric fluxes to further constrain the inversions. The biospheric fluxes were simulated by the Vegetation Photosynthesis and Respiration Model (VPRM) at a resolution of 0.1° and optimized against eddy covariance data. Overall we estimate an a priori uncertainty of 0.54 GtC yr-1 related to the poor spatial representation between the biospheric model and the ecosystem sites. The sink estimated from the atmospheric inversions for the area of Europe (as represented in the model domain) ranges between 0.23 and 0.38 GtC yr-1 (0.39 and 0.71 GtC yr-1 up-scaled to geographical Europe). This is within the range of posterior flux uncertainty estimates of previous studies using ground-based observations.

Importance of crop varieties and management practices: evaluation of a process-based model for simulating CO2 and H2O fluxes at five European maize (Zea mays L.) sites

NARCIS (Netherlands)

Li, L.; Vuichard, N.; Viovy, N.; Ciais, P.; Wang, T.; Ceschia, E.; Jans, W.W.P.; Wattenbach, M.; Beziat, P.; Gruenwald, T.; Lehuger, S.; Bernhofer, C.

2011-01-01

This paper is a modelling study of crop management impacts on carbon and water fluxes at a range of European sites. The model is a crop growth model (STICS) coupled with a process-based land surface model (ORCHIDEE). The data are online eddy-covariance observations of CO2 and H2O fluxes at five

An inorganic CO2 diffusion and dissolution process explains negative CO2 fluxes in saline/alkaline soils

Science.gov (United States)

Ma, Jie; Wang, Zhong-Yuan; Stevenson, Bryan A.; Zheng, Xin-Jun; Li, Yan

2013-01-01

An ‘anomalous' negative flux, in which carbon dioxide (CO2) enters rather than is released from the ground, was studied in a saline/alkaline soil. Soil sterilization disclosed an inorganic process of CO2 dissolution into (during the night) and out of (during the day) the soil solution, driven by variation in soil temperature. Experimental and modeling analysis revealed that pH and soil moisture were the most important determinants of the magnitude of this inorganic CO2 flux. In the extreme cases of air-dried saline/alkaline soils, this inorganic process was predominant. While the diurnal flux measured was zero sum, leaching of the dissolved inorganic carbon in the soil solution could potentially effect net carbon ecosystem exchange. This finding implies that an inorganic module should be incorporated when dealing with the CO2 flux of saline/alkaline land. Neglecting this inorganic flux may induce erroneous or misleading conclusions in interpreting CO2 fluxes of these ecosystems. PMID:23778238

Comparison of regional and ecosystem CO2 fluxes

DEFF Research Database (Denmark)

Gryning, Sven-Erik; Søgaard, Henrik; Batchvarova, Ekaterina

2009-01-01

A budget method to derive the regional surface flux of CO2 from the evolution of the boundary layer is presented and applied. The necessary input for the method can be deduced from a combination of vertical profile measurements of CO2 concentrations by i.e. an airplane, successive radio-soundings......A budget method to derive the regional surface flux of CO2 from the evolution of the boundary layer is presented and applied. The necessary input for the method can be deduced from a combination of vertical profile measurements of CO2 concentrations by i.e. an airplane, successive radio...

Air-ice CO2 fluxes and pCO2 dynamics in the Arctic coastal area (Amundsen Gulf, Canada)

Science.gov (United States)

Geilfus, Nicolas-Xavier; Tison, Jean Louis; Carnat, Gauthier; Else, Brent; Borges, Alberto V.; Thomas, Helmuth; Shadwick, Elizabeth; Delille, Bruno

2010-05-01

Sea ice covers about 7% of the Earth surface at its maximum seasonal extent. For decades sea ice was assumed to be an impermeable and inert barrier for air - sea exchange of CO2 so that global climate models do not include CO2 exchange between the oceans and the atmosphere in the polar regions. However, uptake of atmospheric CO2 by sea ice cover was recently reported raising the need to further investigate pCO2 dynamics in the marine cryosphere realm and related air-ice CO2 fluxes. In addition, budget of CO2 fluxes are poorly constrained in high latitudes continental shelves [Borges et al., 2006]. We report measurements of air-ice CO2 fluxes above the Canadian continental shelf and compare them to previous measurements carried out in Antarctica. We carried out measurements of pCO2 within brines and bulk ice, and related air-ice CO2 fluxes (chamber method) in Antarctic first year pack ice ("Sea Ice Mass Balance in Antarctica -SIMBA" drifting station experiment September - October 2007) and in Arctic first year land fast ice ("Circumpolar Flaw Lead" - CFL, April - June 2008). These 2 experiments were carried out in contrasted sites. SIMBA was carried out on sea ice in early spring while CFL was carried out in from the middle of the winter to the late spring while sea ice was melting. Both in Arctic and Antarctic, no air-ice CO2 fluxes were detected when sea ice interface was below -10°C. Slightly above -10°C, fluxes toward the atmosphere were observed. In contrast, at -7°C fluxes from the atmosphere to the ice were significant. The pCO2 of the brine exhibits a same trend in both hemispheres with a strong decrease of the pCO2 anti-correlated with the increase of sea ice temperature. The pCO2 shifted from a large over-saturation at low temperature to a marked under-saturation at high temperature. These air-ice CO2 fluxes are partly controlled by the permeability of the air-ice interface, which depends of the temperature of this one. Moreover, air-ice CO2 fluxes are

Continuous atmospheric monitoring of the injected CO2 behavior over geological storage sites using flux stations: latest technologies and resources

Science.gov (United States)

Burba, George; Madsen, Rodney; Feese, Kristin

2014-05-01

Flux stations have been widely used to monitor emission rates of CO2 from various ecosystems for climate research for over 30 years [1]. The stations provide accurate and continuous measurements of CO2 emissions with high temporal resolution. Time scales range from 20 times per second for gas concentrations, to 15-minute, hourly, daily, and multi-year periods. The emissions are measured from the upwind area ranging from thousands of square meters to multiple square kilometers, depending on the measurement height. The stations can nearly instantaneously detect rapid changes in emissions due to weather events, as well as changes caused by variations in human-triggered events (pressure leaks, control releases, etc.). Stations can also detect any slow changes related to seasonal dynamics and human-triggered low-frequency processes (leakage diffusion, etc.). In the past, station configuration, data collection and processing were highly-customized, site-specific and greatly dependent on "school-of-thought" practiced by a particular research group. In the last 3-5 years, due to significant efforts of global and regional CO2 monitoring networks (e.g., FluxNet, Ameriflux, Carbo-Europe, ICOS, etc.) and technological developments, the flux station methodology became fairly standardized and processing protocols became quite uniform [1]. A majority of current stations compute CO2 emission rates using the eddy covariance method, one of the most direct and defensible micrometeorological techniques [1]. Presently, over 600 such flux stations are in operation in over 120 countries, using permanent and mobile towers or moving platforms (e.g., automobiles, helicopters, and airplanes). Atmospheric monitoring of emission rates using such stations is now recognized as an effective method in regulatory and industrial applications, including carbon storage [2-8]. Emerging projects utilize flux stations to continuously monitor large areas before and after the injections, to locate and

Eddy covariance carbonyl sulfide flux measurements with a quantum cascade laser absorption spectrometer

Directory of Open Access Journals (Sweden)

K. Gerdel

2017-09-01

Full Text Available The trace gas carbonyl sulfide (COS has lately received growing interest from the eddy covariance (EC community due to its potential to serve as an independent approach for constraining gross primary production and canopy stomatal conductance. Thanks to recent developments of fast-response high-precision trace gas analysers (e.g. quantum cascade laser absorption spectrometers, QCLAS, a handful of EC COS flux measurements have been published since 2013. To date, however, a thorough methodological characterisation of QCLAS with regard to the requirements of the EC technique and the necessary processing steps has not been conducted. The objective of this study is to present a detailed characterisation of the COS measurement with the Aerodyne QCLAS in the context of the EC technique and to recommend best EC processing practices for those measurements. Data were collected from May to October 2015 at a temperate mountain grassland in Tyrol, Austria. Analysis of the Allan variance of high-frequency concentration measurements revealed the occurrence of sensor drift under field conditions after an averaging time of around 50 s. We thus explored the use of two high-pass filtering approaches (linear detrending and recursive filtering as opposed to block averaging and linear interpolation of regular background measurements for covariance computation. Experimental low-pass filtering correction factors were derived from a detailed cospectral analysis. The CO2 and H2O flux measurements obtained with the QCLAS were compared with those obtained with a closed-path infrared gas analyser. Overall, our results suggest small, but systematic differences between the various high-pass filtering scenarios with regard to the fraction of data retained in the quality control and flux magnitudes. When COS and CO2 fluxes are combined in the ecosystem relative uptake rate, systematic differences between the high-pass filtering scenarios largely cancel out, suggesting that

Eddy covariance carbonyl sulphide flux measurements with a quantum cascade laser absorption spectrometer.

Science.gov (United States)

Gerdel, Katharina; Spielmann, Felix Maximilian; Hammerle, Albin; Wohlfahrt, Georg

2017-09-26

The trace gas carbonyl sulphide (COS) has lately received growing interest in the eddy covariance (EC) community due to its potential to serve as an independent approach for constraining gross primary production and canopy stomatal conductance. Thanks to recent developments of fast-response high-precision trace gas analysers (e.g. quantum cascade laser absorption spectrometers (QCLAS)), a handful of EC COS flux measurements have been published since 2013. To date, however, a thorough methodological characterisation of QCLAS with regard to the requirements of the EC technique and the necessary processing steps has not been conducted. The objective of this study is to present a detailed characterization of the COS measurement with the Aerodyne QCLAS in the context of the EC technique, and to recommend best EC processing practices for those measurements. Data were collected from May to October 2015 at a temperate mountain grassland in Tyrol, Austria. Analysis of the Allan variance of high-frequency concentration measurements revealed sensor drift to occur under field conditions after an averaging time of around 50 s. We thus explored the use of two high-pass filtering approaches (linear detrending and recursive filtering) as opposed to block averaging and linear interpolation of regular background measurements for covariance computation. Experimental low-pass filtering correction factors were derived from a detailed cospectral analysis. The CO 2 and H 2 O flux measurements obtained with the QCLAS were compared against those obtained with a closed-path infrared gas analyser. Overall, our results suggest small, but systematic differences between the various high-pass filtering scenarios with regard to the fraction of data retained in the quality control and flux magnitudes. When COS and CO 2 fluxes are combined in the so-called ecosystem relative uptake rate, systematic differences between the high-pass filtering scenarios largely cancel out, suggesting that this

Methane and carbon dioxide fluxes over a lake: comparison between eddy covariance, floating chambers and boundary layer method

Directory of Open Access Journals (Sweden)

K.-M. Erkkilä

2018-01-01

Full Text Available Freshwaters bring a notable contribution to the global carbon budget by emitting both carbon dioxide (CO2 and methane (CH4 to the atmosphere. Global estimates of freshwater emissions traditionally use a wind-speed-based gas transfer velocity, kCC (introduced by Cole and Caraco, 1998, for calculating diffusive flux with the boundary layer method (BLM. We compared CH4 and CO2 fluxes from BLM with kCC and two other gas transfer velocities (kTE and kHE, which include the effects of water-side cooling to the gas transfer besides shear-induced turbulence, with simultaneous eddy covariance (EC and floating chamber (FC fluxes during a 16-day measurement campaign in September 2014 at Lake Kuivajärvi in Finland. The measurements included both lake stratification and water column mixing periods. Results show that BLM fluxes were mainly lower than EC, with the more recent model kTE giving the best fit with EC fluxes, whereas FC measurements resulted in higher fluxes than simultaneous EC measurements. We highly recommend using up-to-date gas transfer models, instead of kCC, for better flux estimates. BLM CO2 flux measurements had clear differences between daytime and night-time fluxes with all gas transfer models during both stratified and mixing periods, whereas EC measurements did not show a diurnal behaviour in CO2 flux. CH4 flux had higher values in daytime than night-time during lake mixing period according to EC measurements, with highest fluxes detected just before sunset. In addition, we found clear differences in daytime and night-time concentration difference between the air and surface water for both CH4 and CO2. This might lead to biased flux estimates, if only daytime values are used in BLM upscaling and flux measurements in general. FC measurements did not detect spatial variation in either CH4 or CO2 flux over Lake Kuivajärvi. EC measurements, on the other hand, did not show any spatial variation in CH4 fluxes but did show a clear difference

Implications of overestimated anthropogenic CO2 emissions on East Asian and global land CO2 flux inversion

Science.gov (United States)

Saeki, Tazu; Patra, Prabir K.

2017-12-01

Measurement and modelling of regional or country-level carbon dioxide (CO2) fluxes are becoming critical for verification of the greenhouse gases emission control. One of the commonly adopted approaches is inverse modelling, where CO2 fluxes (emission: positive flux, sink: negative flux) from the terrestrial ecosystems are estimated by combining atmospheric CO2 measurements with atmospheric transport models. The inverse models assume anthropogenic emissions are known, and thus the uncertainties in the emissions introduce systematic bias in estimation of the terrestrial (residual) fluxes by inverse modelling. Here we show that the CO2 sink increase, estimated by the inverse model, over East Asia (China, Japan, Korea and Mongolia), by about 0.26 PgC year-1 (1 Pg = 1012 g) during 2001-2010, is likely to be an artifact of the anthropogenic CO2 emissions increasing too quickly in China by 1.41 PgC year-1. Independent results from methane (CH4) inversion suggested about 41% lower rate of East Asian CH4 emission increase during 2002-2012. We apply a scaling factor of 0.59, based on CH4 inversion, to the rate of anthropogenic CO2 emission increase since the anthropogenic emissions of both CO2 and CH4 increase linearly in the emission inventory. We find no systematic increase in land CO2 uptake over East Asia during 1993-2010 or 2000-2009 when scaled anthropogenic CO2 emissions are used, and that there is a need of higher emission increase rate for 2010-2012 compared to those calculated by the inventory methods. High bias in anthropogenic CO2 emissions leads to stronger land sinks in global land-ocean flux partitioning in our inverse model. The corrected anthropogenic CO2 emissions also produce measurable reductions in the rate of global land CO2 sink increase post-2002, leading to a better agreement with the terrestrial biospheric model simulations that include CO2-fertilization and climate effects.

Isotopic versus micrometeorologic ocean CO2 fluxes: A serious conflict

International Nuclear Information System (INIS)

Broecker, W.S.; Ledwell, J.R.; Takahashi, T.; Weiss, R.; Merlivat, L.; Memery, L.; Tsung-Hung Peng; Jahne, B.; Otto Munnich, K.

1986-01-01

Eddy correlation measurements over the ocean give CO 2 fluxes an order of magnitude or more larger than expected from mass balance or more larger than expected from mass balance measurements using radiocarbon and radon 222. In particular, Smith and Jones (1985) reported large upward and downward fluxes in a surf zone at supersaturations of 15% and attributed them to the equilibration of bubbles at elevated pressures. They argue that even on the open ocean such bubble injection may create steady state CO 2 supersaturations and that inferences of fluxes based on air-sea pCO 2 differences and radon exchange velocities must be made with caution. We defend the global average CO 2 exchange rate determined by three independent radioisotopic means: prebomb radiocarbon inventories; global surveys of mixed layer radon deficits; and oceanic uptake of bomb-produced radiocarbon. We argue that laboratory and lake data do not lead one to expect fluxes as large as reported from the eddy correlation technique; that the radon method of determining exchange velocities is indeed useful for estimating CO 2 fluxes; that supersaturations of CO 2 due to bubble injection on the open ocean are negligible; that the hypothesis that Smith and Jones advance cannot account for the fluxes that they report; and that the pCO 2 values reported by Smith and Jones are likely to be systematically much too high. The CO 2 fluxes for the ocean measured to data by the micrometeorological method can be reconciled with neither the observed concentrations of radioisotopes of radon and carbon in the oceans nor the tracer experiments carried out in lakes and in wind/wave tunnels

Comparison of CO2 and H2O fluxes over grassland vegetations measured by the eddy-covariance technique and by open system chamber

Czech Academy of Sciences Publication Activity Database

Balogh, J.; Nagy, Z.; Fóti, S.; Pintér, K.; Czóbel, S.; Péli, E.; Acosta, Manuel; Marek, Michal V.; Csintalan, Z.; Tuba, Z.

2007-01-01

Roč. 45, č. 2 (2007), s. 288-292 ISSN 0300-3604 Institutional research plan: CEZ:AV0Z60870520 Keywords : CO2 and H2O fluxes * leaf area index * grassland * EC Subject RIV: EH - Ecology, Behaviour Impact factor: 0.976, year: 2007

Evaluation of Deep Learning Models for Predicting CO2 Flux

Science.gov (United States)

Halem, M.; Nguyen, P.; Frankel, D.

2017-12-01

Artificial neural networks have been employed to calculate surface flux measurements from station data because they are able to fit highly nonlinear relations between input and output variables without knowing the detail relationships between the variables. However, the accuracy in performing neural net estimates of CO2 flux from observations of CO2 and other atmospheric variables is influenced by the architecture of the neural model, the availability, and complexity of interactions between physical variables such as wind, temperature, and indirect variables like latent heat, and sensible heat, etc. We evaluate two deep learning models, feed forward and recurrent neural network models to learn how they each respond to the physical measurements, time dependency of the measurements of CO2 concentration, humidity, pressure, temperature, wind speed etc. for predicting the CO2 flux. In this paper, we focus on a) building neural network models for estimating CO2 flux based on DOE data from tower Atmospheric Radiation Measurement data; b) evaluating the impact of choosing the surface variables and model hyper-parameters on the accuracy and predictions of surface flux; c) assessing the applicability of the neural network models on estimate CO2 flux by using OCO-2 satellite data; d) studying the efficiency of using GPU-acceleration for neural network performance using IBM Power AI deep learning software and packages on IBM Minsky system.

Estimating local atmosphere-surface fluxes using eddy covariance and numerical Ogive optimization

DEFF Research Database (Denmark)

Sievers, Jakob; Papakyriakou, Tim; Larsen, Søren

2014-01-01

Estimating representative surface-fluxes using eddy covariance leads invariably to questions concerning inclusion or exclusion of low-frequency flux contributions. For studies where fluxes are linked to local physical parameters and up-scaled through numerical modeling efforts, low-frequency cont......Estimating representative surface-fluxes using eddy covariance leads invariably to questions concerning inclusion or exclusion of low-frequency flux contributions. For studies where fluxes are linked to local physical parameters and up-scaled through numerical modeling efforts, low...

Toward an estimation of daily european CO{sub 2} fluxes at high spatial resolution by inversion of atmospheric transport; Vers une estimation des flux de CO{sub 2} journaliers europeens a haute resolution par inversion du transport atmospherique

Energy Technology Data Exchange (ETDEWEB)

Carouge, C

2006-04-15

Since the end of the 1980's, measurements of atmospheric carbon dioxide have been used to estimate global and regional fluxes of CO{sub 2}. This is possible because CO{sub 2} concentration variation is directly linked to flux variation by atmospheric transport. We can find the spatial and temporal distribution of fluxes from concentration measurements by 'inverting' the atmospheric transport. Until recently, most CO{sub 2} inversions have used monthly mean CO{sub 2} atmospheric concentration measurements to infer monthly fluxes. Considering the sparseness of the global CO{sub 2} measurement network, fluxes were a priori aggregated on sub-continental regions and distributed on a fixed spatial pattern within these regions. Only one flux coefficient per month for each region was optimized. With this strong constraint, estimated fluxes can be biased by non-perfect distribution of fluxes within each region (aggregation error). Therefore, flux estimation at model resolution is being developed where the hard constraint of a fixed distribution within a region is replaced by a soft constraint of covariances between flux uncertainties. The use of continuous observations from an increasing number of measurement sites offers a new challenge for inverse modelers. We investigate the use of daily averaged observations to infer daily CO{sub 2} fluxes at model resolution over Europe. We have developed a global synthesis Bayesian inversion to invert daily fluxes at model resolution (50 x 50 km over Europe) from daily averaged CO{sub 2} concentrations. We have obtained estimated fluxes for the year 2001 over Europe using the 10 European continuous sites from the AEROCARB network. The global atmospheric model LMDZt is used with a nested grid over Europe. It is necessary to add a priori spatial and temporal correlations between flux errors to constrain the Bayesian inversion. We present the impact on estimated fluxes of three different spatial correlations based on

Eddy covariance flux measurements of gaseous elemental mercury using cavity ring-down spectroscopy.

Science.gov (United States)

Pierce, Ashley M; Moore, Christopher W; Wohlfahrt, Georg; Hörtnagl, Lukas; Kljun, Natascha; Obrist, Daniel

2015-02-03

A newly developed pulsed cavity ring-down spectroscopy (CRDS) system for measuring atmospheric gaseous elemental mercury (GEM) concentrations at high temporal resolution (25 Hz) was used to successfully conduct the first eddy covariance (EC) flux measurements of GEM. GEM is the main gaseous atmospheric form, and quantification of bidirectional exchange between the Earth's surface and the atmosphere is important because gas exchange is important on a global scale. For example, surface GEM emissions from natural sources, legacy emissions, and re-emission of previously deposited anthropogenic pollution may exceed direct primary anthropogenic emissions. Using the EC technique for flux measurements requires subsecond measurements, which so far has not been feasible because of the slow time response of available instrumentation. The CRDS system measured GEM fluxes, which were compared to fluxes measured with the modified Bowen ratio (MBR) and a dynamic flux chamber (DFC). Measurements took place near Reno, NV, in September and October 2012 encompassing natural, low-mercury (Hg) background soils and Hg-enriched soils. During nine days of measurements with deployment of Hg-enriched soil in boxes within 60 m upwind of the EC tower, the covariance of GEM concentration and vertical wind speed was measured, showing that EC fluxes over an Hg-enriched area were detectable. During three separate days of flux measurements over background soils (without Hg-enriched soils), no covariance was detected, indicating fluxes below the detection limit. When fluxes were measurable, they strongly correlated with wind direction; the highest fluxes occurred when winds originated from the Hg-enriched area. Comparisons among the three methods showed good agreement in direction (e.g., emission or deposition) and magnitude, especially when measured fluxes originated within the Hg-enriched soil area. EC fluxes averaged 849 ng m(-2) h(-1), compared to DFC fluxes of 1105 ng m(-2) h(-1) and MBR fluxes

Using eddy covariance of CO2, 13CO2 and CH4, continuous soil respiration measurements, and PhenoCams to constrain a process-based biogeochemical model for carbon market-funded wetland restoration

Science.gov (United States)

Oikawa, P. Y.; Baldocchi, D. D.; Knox, S. H.; Sturtevant, C. S.; Verfaillie, J. G.; Dronova, I.; Jenerette, D.; Poindexter, C.; Huang, Y. W.

2015-12-01

We use multiple data streams in a model-data fusion approach to reduce uncertainty in predicting CO2 and CH4 exchange in drained and flooded peatlands. Drained peatlands in the Sacramento-San Joaquin River Delta, California are a strong source of CO2 to the atmosphere and flooded peatlands or wetlands are a strong CO2 sink. However, wetlands are also large sources of CH4 that can offset the greenhouse gas mitigation potential of wetland restoration. Reducing uncertainty in model predictions of annual CO2 and CH4 budgets is critical for including wetland restoration in Cap-and-Trade programs. We have developed and parameterized the Peatland Ecosystem Photosynthesis, Respiration, and Methane Transport model (PEPRMT) in a drained agricultural peatland and a restored wetland. Both ecosystem respiration (Reco) and CH4 production are a function of 2 soil carbon (C) pools (i.e. recently-fixed C and soil organic C), temperature, and water table height. Photosynthesis is predicted using a light use efficiency model. To estimate parameters we use a Markov Chain Monte Carlo approach with an adaptive Metropolis-Hastings algorithm. Multiple data streams are used to constrain model parameters including eddy covariance of CO2, 13CO2 and CH4, continuous soil respiration measurements and digital photography. Digital photography is used to estimate leaf area index, an important input variable for the photosynthesis model. Soil respiration and 13CO2 fluxes allow partitioning of eddy covariance data between Reco and photosynthesis. Partitioned fluxes of CO2 with associated uncertainty are used to parametrize the Reco and photosynthesis models within PEPRMT. Overall, PEPRMT model performance is high. For example, we observe high data-model agreement between modeled and observed partitioned Reco (r2 = 0.68; slope = 1; RMSE = 0.59 g C-CO2 m-2 d-1). Model validation demonstrated the model's ability to accurately predict annual budgets of CO2 and CH4 in a wetland system (within 14% and 1

Using eddy covariance to measure the dependence of air-sea CO2 exchange rate on friction velocity

Science.gov (United States)

Landwehr, Sebastian; Miller, Scott D.; Smith, Murray J.; Bell, Thomas G.; Saltzman, Eric S.; Ward, Brian

2018-03-01

Parameterisation of the air-sea gas transfer velocity of CO2 and other trace gases under open-ocean conditions has been a focus of air-sea interaction research and is required for accurately determining ocean carbon uptake. Ships are the most widely used platform for air-sea flux measurements but the quality of the data can be compromised by airflow distortion and sensor cross-sensitivity effects. Recent improvements in the understanding of these effects have led to enhanced corrections to the shipboard eddy covariance (EC) measurements.Here, we present a revised analysis of eddy covariance measurements of air-sea CO2 and momentum fluxes from the Southern Ocean Surface Ocean Aerosol Production (SOAP) study. We show that it is possible to significantly reduce the scatter in the EC data and achieve consistency between measurements taken on station and with the ship underway. The gas transfer velocities from the EC measurements correlate better with the EC friction velocity (u*) than with mean wind speeds derived from shipboard measurements corrected with an airflow distortion model. For the observed range of wind speeds (u10 N = 3-23 m s-1), the transfer velocities can be parameterised with a linear fit to u*. The SOAP data are compared to previous gas transfer parameterisations using u10 N computed from the EC friction velocity with the drag coefficient from the Coupled Ocean-Atmosphere Response Experiment (COARE) model version 3.5. The SOAP results are consistent with previous gas transfer studies, but at high wind speeds they do not support the sharp increase in gas transfer associated with bubble-mediated transfer predicted by physically based models.

Global monthly CO2 flux inversion with a focus over North America

International Nuclear Information System (INIS)

Feng Deng; Chen, Jing M.; Ishizawa, Misa; Chiu-Wai Yuen; Gang Mo; Higuchi, Kaz; Chan, Douglas; Maksyutov, Shamil

2007-01-01

A nested inverse modelling system was developed for estimating carbon fluxes of 30 regions in North America and 20 regions for the rest of the globe. Monthly inverse modelling was conducted using CO 2 concentration measurements of 3 yr (2001-2003) at 88 sites. Inversion results show that in 2003 the global carbon sink is -2.76 ± 0.55 Pg C. Oceans and lands are responsible for 88.5% and 11.5% of the sink, respectively. Northern lands are the largest sinks with North America contributing a sink of -0.97 ± 0.21 Pg C in 2003, of which Canada's sink is -0.34 ± 0.14 Pg C. For Canada, the inverse results show a spatial pattern in agreement, for the most part, with a carbon source and sink distribution map previously derived through ecosystem modelling. However, discrepancies in the spatial pattern and in flux magnitude between these two estimates exist in certain regions. Numerical experiments with a full covariance matrix, with the consideration of the error structure of the a priori flux field based on meteorological variables among the 30 North America regions, resulted in a small but meaningful improvement in the inverted fluxes. Uncertainty reduction analysis suggests that new observation sites are still needed to further improve the inversion for these 30 regions in North America

Toward an estimation of daily european CO2 fluxes at high spatial resolution by inversion of atmospheric transport

International Nuclear Information System (INIS)

Carouge, C.

2006-04-01

Since the end of the 1980's, measurements of atmospheric carbon dioxide have been used to estimate global and regional fluxes of CO 2 . This is possible because CO 2 concentration variation is directly linked to flux variation by atmospheric transport. We can find the spatial and temporal distribution of fluxes from concentration measurements by 'inverting' the atmospheric transport. Until recently, most CO 2 inversions have used monthly mean CO 2 atmospheric concentration measurements to infer monthly fluxes. Considering the sparseness of the global CO 2 measurement network, fluxes were a priori aggregated on sub-continental regions and distributed on a fixed spatial pattern within these regions. Only one flux coefficient per month for each region was optimized. With this strong constraint, estimated fluxes can be biased by non-perfect distribution of fluxes within each region (aggregation error). Therefore, flux estimation at model resolution is being developed where the hard constraint of a fixed distribution within a region is replaced by a soft constraint of covariances between flux uncertainties. The use of continuous observations from an increasing number of measurement sites offers a new challenge for inverse modelers. We investigate the use of daily averaged observations to infer daily CO 2 fluxes at model resolution over Europe. We have developed a global synthesis Bayesian inversion to invert daily fluxes at model resolution (50 x 50 km over Europe) from daily averaged CO 2 concentrations. We have obtained estimated fluxes for the year 2001 over Europe using the 10 European continuous sites from the AEROCARB network. The global atmospheric model LMDZt is used with a nested grid over Europe. It is necessary to add a priori spatial and temporal correlations between flux errors to constrain the Bayesian inversion. We present the impact on estimated fluxes of three different spatial correlations based on distance between pixels, climate and vegetation

Quantitative comparison of in situ soil CO2 flux measurement methods

Science.gov (United States)

Jennifer D. Knoepp; James M. Vose

2002-01-01

Development of reliable regional or global carbon budgets requires accurate measurement of soil CO2 flux. We conducted laboratory and field studies to determine the accuracy and comparability of methods commonly used to measure in situ soil CO2 fluxes. Methods compared included CO2...

A Comparison of Three Gap Filling Techniques for Eddy Covariance Net Carbon Fluxes in Short Vegetation Ecosystems

Directory of Open Access Journals (Sweden)

Xiaosong Zhao

2015-01-01

Full Text Available Missing data is an inevitable problem when measuring CO2, water, and energy fluxes between biosphere and atmosphere by eddy covariance systems. To find the optimum gap-filling method for short vegetations, we review three-methods mean diurnal variation (MDV, look-up tables (LUT, and nonlinear regression (NLR for estimating missing values of net ecosystem CO2 exchange (NEE in eddy covariance time series and evaluate their performance for different artificial gap scenarios based on benchmark datasets from marsh and cropland sites in China. The cumulative errors for three methods have no consistent bias trends, which ranged between −30 and +30 mgCO2 m−2 from May to October at three sites. To reduce sum bias in maximum, combined gap-filling methods were selected for short vegetation. The NLR or LUT method was selected after plant rapidly increasing in spring and before the end of plant growing, and MDV method was used to the other stage. The sum relative error (SRE of optimum method ranged between −2 and +4% for four-gap level at three sites, except for 55% gaps at soybean site, which also obviously reduced standard deviation of error.

Quantifying the drivers of ocean-atmosphere CO2 fluxes

Science.gov (United States)

Lauderdale, Jonathan M.; Dutkiewicz, Stephanie; Williams, Richard G.; Follows, Michael J.

2016-07-01

A mechanistic framework for quantitatively mapping the regional drivers of air-sea CO2 fluxes at a global scale is developed. The framework evaluates the interplay between (1) surface heat and freshwater fluxes that influence the potential saturated carbon concentration, which depends on changes in sea surface temperature, salinity and alkalinity, (2) a residual, disequilibrium flux influenced by upwelling and entrainment of remineralized carbon- and nutrient-rich waters from the ocean interior, as well as rapid subduction of surface waters, (3) carbon uptake and export by biological activity as both soft tissue and carbonate, and (4) the effect on surface carbon concentrations due to freshwater precipitation or evaporation. In a steady state simulation of a coarse-resolution ocean circulation and biogeochemistry model, the sum of the individually determined components is close to the known total flux of the simulation. The leading order balance, identified in different dynamical regimes, is between the CO2 fluxes driven by surface heat fluxes and a combination of biologically driven carbon uptake and disequilibrium-driven carbon outgassing. The framework is still able to reconstruct simulated fluxes when evaluated using monthly averaged data and takes a form that can be applied consistently in models of different complexity and observations of the ocean. In this way, the framework may reveal differences in the balance of drivers acting across an ensemble of climate model simulations or be applied to an analysis and interpretation of the observed, real-world air-sea flux of CO2.

Progress Toward Measuring CO2 Isotopologue Fluxes in situ with the LLNL Miniature, Laser-based CO2 Sensor

Science.gov (United States)

Osuna, J. L.; Bora, M.; Bond, T.

2015-12-01

One method to constrain photosynthesis and respiration independently at the ecosystem scale is to measure the fluxes of CO2­ isotopologues. Instrumentation is currently available to makes these measurements but they are generally costly, large, bench-top instruments. Here, we present progress toward developing a laser-based sensor that can be deployed directly to a canopy to passively measure CO2 isotopologue fluxes. In this study, we perform initial proof-of-concept and sensor characterization tests in the laboratory and in the field to demonstrate performance of the Lawrence Livermore National Laboratory (LLNL) tunable diode laser flux sensor. The results shown herein demonstrate measurement of bulk CO2 as a first step toward achieving flux measurements of CO2 isotopologues. The sensor uses a Vertical Cavity Surface Emitting Laser (VCSEL) in the 2012 nm range. The laser is mounted in a multi-pass White Cell. In order to amplify the absorption signal of CO2 in this range we employ wave modulation spectroscopy, introducing an alternating current (AC) bias component where f is the frequency of modulation on the laser drive current in addition to the direct current (DC) emission scanning component. We observed a strong linear relationship (r2 = 0.998 and r2 = 0.978 at all and low CO2 concentrations, respectively) between the 2f signal and the CO2 concentration in the cell across the range of CO2 concentrations relevant for flux measurements. We use this calibration to interpret CO2 concentration of a gas flowing through the White cell in the laboratory and deployed over a grassy field. We will discuss sensor performance in the lab and in situ as well as address steps toward achieving canopy-deployed, passive measurements of CO2 isotopologue fluxes. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-675788

Preliminary estimation of Vulcano of CO2 budget and continuous monitoring of summit soil CO2 flux

OpenAIRE

Inguaggiato, S.; Mazot, A.; Diliberto, I. S.; Rouwet, D.; Vita, F.; Capasso, G.; Bobrowski, N.; Inguaggiato, C.; Grassa, F.

2008-01-01

Total CO2 output from fumaroles, soil gases, bubbling and water dissolved gases were estimated at Vulcano Island, Italy. The fumaroles output has been estimated from SO2 plume flux, while soil flux emission has been carried out through 730 CO2 fluxes measured on the island surface, performed by means of accumulation chamber method. Vulcano Island, located in the Aeolian Archipelago, is an active volcano that has been in state of solphataric activity, since the last eru...

Are Low-order Covariance Estimates Useful in Error Analyses?

Science.gov (United States)

Baker, D. F.; Schimel, D.

2005-12-01

Atmospheric trace gas inversions, using modeled atmospheric transport to infer surface sources and sinks from measured concentrations, are most commonly done using least-squares techniques that return not only an estimate of the state (the surface fluxes) but also the covariance matrix describing the uncertainty in that estimate. Besides allowing one to place error bars around the estimate, the covariance matrix may be used in simulation studies to learn what uncertainties would be expected from various hypothetical observing strategies. This error analysis capability is routinely used in designing instrumentation, measurement campaigns, and satellite observing strategies. For example, Rayner, et al (2002) examined the ability of satellite-based column-integrated CO2 measurements to constrain monthly-average CO2 fluxes for about 100 emission regions using this approach. Exact solutions for both state vector and covariance matrix become computationally infeasible, however, when the surface fluxes are solved at finer resolution (e.g., daily in time, under 500 km in space). It is precisely at these finer scales, however, that one would hope to be able to estimate fluxes using high-density satellite measurements. Non-exact estimation methods such as variational data assimilation or the ensemble Kalman filter could be used, but they achieve their computational savings by obtaining an only approximate state estimate and a low-order approximation of the true covariance. One would like to be able to use this covariance matrix to do the same sort of error analyses as are done with the full-rank covariance, but is it correct to do so? Here we compare uncertainties and `information content' derived from full-rank covariance matrices obtained from a direct, batch least squares inversion to those from the incomplete-rank covariance matrices given by a variational data assimilation approach solved with a variable metric minimization technique (the Broyden-Fletcher- Goldfarb

NEON's Eddy-Covariance Storage Exchange: from Tower to Data Portal

Science.gov (United States)

Durden, N. P.; Luo, H.; Xu, K.; Metzger, S.; Durden, D.

2017-12-01

NEON's eddy-covariance storage exchange system (ECSE) consists of a suite of sensors including temperature sensors, a CO2 and H2O gas analyzer, and isotopic CO2 and H2O analyzers. NEON's ECSE was developed to provide the vertical profile measurements of temperature, CO2 and H2O concentrations, the stable isotope ratios in CO2 (δ13C) and H2O (δ18O and δ2H) in the atmosphere. The profiles of temperature and concentrations of CO2 and H2O are key to calculate storage fluxes for eddy-covariance tower sites. Storage fluxes have a strong diurnal cycle and can be large in magnitude, especially at temporal scales less than one day. However, the storage term is often neglected in flux computations. To obtian accurate eddy-covariance fluxes, the storage fluxes are calculated and incorporated into the calculations of net surface-atmosphere ecosystem exchange of heat, CO2, and H2O for each NEON tower site. Once the ECSE raw data (Level 0, or L0) is retrieved at NEON's headquarters, it is preconditioned through a sequence of unit conversion, time regularization, and plausibility tests. By utilizing NEON's eddy4R framework (Metzger et al., 2017), higher-level data products are generated including: Level 1 (L1): Measurement-level specific averages of temperature and concentrations of CO2 and H2O. Level 2 (L2): Time rate of change of temperature and concentrations of CO2 and H2O over 30 min at each measurement level along the vertical tower profile. Level 3 (L3): Time rate of change of temperature and concentrations of CO2 and H2O over 30 min (L2), spatially interpolated along the vertical tower profile. Level 4 (L4): Storage fluxes of heat, CO2, and H2O calculated from the integrated time rate of change spatially interpolated profile (L3). The L4 storage fluxes are combined with turbulent fluxes to calculate the net surface-atmosphere ecosystem exchange of heat, CO2, and H2O. Moreover, a final quality flag and uncertainty budget are produced individually for each data stream

Chambers versus Relaxed Eddy Accumulation: an intercomparison study of two methods for short-term measurements of biogenic CO2 fluxes

Science.gov (United States)

Jasek, Alina; Zimnoch, Miroslaw; Gorczyca, Zbigniew; Chmura, Lukasz; Necki, Jaroslaw

2014-05-01

The presented work is a part of comprehensive study aimed at thorough characterization of carbon cycle in the urban environment of Krakow, southern Poland. In the framework of this study two independent methods were employed to quantify biogenic CO2 flux in the city: (i) closed chambers, and (ii) Relaxed Eddy Accumulation (REA). The results of a three-day intensive intercomparison campaign performed in July 2013 and utilizing both measurement methods are reported here. The chamber method is a widely used approach for measurements of gas exchange between the soil and the atmosphere. The system implemented in this study consisted of a single chamber operating in a closed-dynamic mode, combined with Vaisala CarboCAP infrared CO2 sensor in a mobile setup. An alternative flux measurement method, covering larger area is represented by REA, which is a modification of the eddy covariance method. It consists of a 3D anemometer (Gill Windmaster Pro) and the system collecting updraft and downdraft samples to 5-litre Tedlar bags. The CO2 mixing ratios in the collected samples are measured by Picarro G2101i analyzer. The setup consists of two sets of bags so that the sampling can be performed continuously with 15-min temporal resolution. A 48-hectares open meadow located close the city center was chosen as a test site for comparison of the two methods of CO2 flux measurements outlined above. In the middle of the meadow a 3-metre high tripod was installed with the anemometer and REA inlet system. For a period of 46 hours the system was measuring net CO2 flux from the surrounding area. A meteorological conditions and intensity of photosynthetically active radiation (PAR) were also recorded. In the same time, CO2 flux from several points around the REA inlet was measured with the chamber system, resulting in 93 values for both respiration and net CO2 flux. Chamber results show rather homogenous distribution of the soil CO2 flux (the mean value equal to 40.9 ± 2.2 mmol/m2h), with

Soil surface CO2 fluxes and the carbon budget of a grassland

Science.gov (United States)

Norman, J. M.; Garcia, R.; Verma, S. B.

1992-01-01

Measurements of soil surface CO2 fluxes are reported for three sites within the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) area, and simple empirical equations are fit to the data to provide predictions of soil fluxes from environmental observations. A prototype soil chamber, used to make the flux measurements, is described and tested by comparing CO2 flux measurements to a 40-L chamber, a 1-m/cu chamber, and eddy correlation. Results suggest that flux measurements with the prototype chamber are consistent with measurements by other methods to within about 20 percent. A simple empirical equation based on 10-cm soil temperature, 0- to 10-cm soil volumetric water content, and leaf area index predicts the soil surface CO2 flux with a rms error of 1.2 micro-mol sq m/s for all three sites. Further evidence supports using this equation to evaluate soil surface CO2 during the 1987 FIFE experiment. The soil surface CO2 fluxes when averaged over 24 hours are comparable to daily gross canopy photosynthetic rates. For 6 days of data the net daily accumulation of carbon is about 0.6 g CO2 sq m/d; this is only a few percent of the daily gross accumulation of carbon by photosynthesis. As the soil became drier in 1989, the net accumulation of carbon by the prairie increased, suggesting that the soil flux is more sensitive to temperature and drought than the photosynthetic fluxes.

Annual and seasonal CO2 fluxes from Russian southern taiga soils

International Nuclear Information System (INIS)

Kurganova, I.; Lopes De Gerenyu, V.; Rozanova, L.; Sapronov, D.; Myakshina, T.; Kudeyarov, V.

2003-01-01

Annual and seasonal characteristics of CO 2 emission from five different ecosystems were studied in situ (Russia, Moscow Region) from November 1997 through October 2000. The annual behaviour of the soil respiration rate is influenced by weather conditions during a particular year. Annual CO 2 fluxes from the soils depend on land use of the soils and averaged 684 and 906 g C/m 2 from sandy Albeluvisols (sod-podzolic soils) under forest and grassland, respectively. Annual emission from clay Phaeozems (grey forest soils) was lower and ranged from 422 to 660 g C/m 2 ; the order of precedence was arable 2 fluxes caused by weather conditions ranged from 18% (forest ecosystem on Phaeozems) to 31% (agro-ecosystem). The contribution from the cold period (with snow, November-April) to the annual CO 2 flux was substantial and averaged 21% and 14% for natural and agricultural ecosystems, respectively. The CO 2 fluxes comprised approximately 48-51% in summer, 23-24% in autumn, 18-20% in spring and 7-10% in winter of the total annual carbon dioxide flux

The role of metabolism in modulating CO2 fluxes in boreal lakes

Science.gov (United States)

Bogard, Matthew J.; del Giorgio, Paul A.

2016-10-01

Lake CO2 emissions are increasingly recognized as an important component of the global CO2 cycle, yet the origin of these emissions is not clear, as specific contributions from metabolism and in-lake cycling, versus external inputs, are not well defined. To assess the coupling of lake metabolism with CO2 concentrations and fluxes, we estimated steady state ratios of gross primary production to respiration (GPP:R) and rates of net ecosystem production (NEP = GPP-R) from surface water O2 dynamics (concentration and stable isotopes) in 187 boreal lakes spanning long environmental gradients. Our findings suggest that internal metabolism plays a dominant role in regulating CO2 fluxes in most lakes, but this pattern only emerges when examined at a resolution that accounts for the vastly differing relationships between lake metabolism and CO2 fluxes. Fluxes of CO2 exceeded those from NEP in over half the lakes, but unexpectedly, these effects were most common and typically largest in a subset ( 30% of total) of net autotrophic lakes that nevertheless emitted CO2. Equally surprising, we found no environmental characteristics that distinguished this category from the more common net heterotrophic, CO2 outgassing lakes. Excess CO2 fluxes relative to NEP were best predicted by catchment structure and hydrologic properties, and we infer from a combination of methods that both catchment inputs and internal anaerobic processes may have contributed this excess CO2. Together, our findings show that the link between lake metabolism and CO2 fluxes is often strong but can vary widely across the boreal biome, having important implications for catchment-wide C budgets.

Annual CO2 budget and seasonal CO2 exchange signals at a high Arctic permafrost site on Spitsbergen, Svalbard archipelago

DEFF Research Database (Denmark)

Luërs, J.; Westermann, Signe; Piel, K.

2014-01-01

-lasting snow cover, and several months of darkness. This study presents a complete annual cycle of the CO2 net ecosystem exchange (NEE) dynamics for a high Arctic tundra area at the west coast of Svalbard based on eddy covariance flux measurements. The annual cumulative CO2 budget is close to 0 g C m-2 yr-1...

Soil surface CO2 flux in a boreal black spruce fire chronosequence

Science.gov (United States)

Wang, Chuankuan; Bond-Lamberty, Ben; Gower, Stith T.

2003-02-01

Understanding the effects of wildfire on the carbon (C) cycle of boreal forests is essential to quantifying the role of boreal forests in the global carbon cycle. Soil surface CO2 flux (Rs), the second largest C flux in boreal forests, is directly and indirectly affected by fire and is hypothesized to change during forest succession following fire. The overall objective of this study was to measure and model Rs for a black spruce (Picea mariana [Mill.] BSP) postfire chronosequence in northern Manitoba, Canada. The experiment design was a nested factorial that included two soil drainage classes (well and poorly drained) × seven postfire aged stands. Specific objectives were (1) to quantify the relationship between Rs and soil temperature for different aged boreal black spruce forests in well-drained and poorly drained soil conditions, (2) to examine Rs dynamics along postfire successional stands, and (3) to estimate annual soil surface CO2 flux for these ecosystems. Soil surface CO2 flux was significantly affected by soil drainage class (p = 0.014) and stand age (p = 0.006). Soil surface CO2 flux was positively correlated to soil temperature (R2 = 0.78, p aged stand combination. Soil surface CO2 flux was significantly greater at the well-drained than the poorly drained stands (p = 0.007) during growing season. Annual soil surface CO2 flux for the 1998, 1995, 1989, 1981, 1964, 1930, and 1870 burned stands averaged 226, 412, 357, 413, 350, 274, and 244 g C m-2 yr-1 in the well-drained stands and 146, 380, 300, 303, 256, 233, and 264 g C m-2 yr-1 in the poorly drained stands. Soil surface CO2 flux during the winter (from 1 November to 30 April) comprised from 5 to 19% of the total annual Rs. We speculate that the smaller soil surface CO2 flux in the recently burned than the older stands is mainly caused by decreased root respiration.

Comparing inversion techniques for constraining CO2 fluxes in the Brazilian Amazon Basin with aircraft observations

Science.gov (United States)

Chow, V. Y.; Gerbig, C.; Longo, M.; Koch, F.; Nehrkorn, T.; Eluszkiewicz, J.; Ceballos, J. C.; Longo, K.; Wofsy, S. C.

2012-12-01

The Balanço Atmosférico Regional de Carbono na Amazônia (BARCA) aircraft program spanned the dry to wet and wet to dry transition seasons in November 2008 & May 2009 respectively. It resulted in ~150 vertical profiles covering the Brazilian Amazon Basin (BAB). With the data we attempt to estimate a carbon budget for the BAB, to determine if regional aircraft experiments can provide strong constraints for a budget, and to compare inversion frameworks when optimizing flux estimates. We use a LPDM to integrate satellite-, aircraft-, & surface-data with mesoscale meteorological fields to link bottom-up and top-down models to provide constraints and error bounds for regional fluxes. The Stochastic Time-Inverted Lagrangian Transport (STILT) model driven by meteorological fields from BRAMS, ECMWF, and WRF are coupled to a biosphere model, the Vegetation Photosynthesis Respiration Model (VPRM), to determine regional CO2 fluxes for the BAB. The VPRM is a prognostic biosphere model driven by MODIS 8-day EVI and LSWI indices along with shortwave radiation and temperature from tower measurements and mesoscale meteorological data. VPRM parameters are tuned using eddy flux tower data from the Large-Scale Biosphere Atmosphere experiment. VPRM computes hourly CO2 fluxes by calculating Gross Ecosystem Exchange (GEE) and Respiration (R) for 8 different vegetation types. The VPRM fluxes are scaled up to the BAB by using time-averaged drivers (shortwave radiation & temperature) from high-temporal resolution runs of BRAMS, ECMWF, and WRF and vegetation maps from SYNMAP and IGBP2007. Shortwave radiation from each mesoscale model is validated using surface data and output from GL 1.2, a global radiation model based on GOES 8 visible imagery. The vegetation maps are updated to 2008 and 2009 using landuse scenarios modeled by Sim Amazonia 2 and Sim Brazil. A priori fluxes modeled by STILT-VPRM are optimized using data from BARCA, eddy covariance sites, and flask measurements. The

Hybrid inversions of CO2 fluxes at regional scale applied to network design

Science.gov (United States)

Kountouris, Panagiotis; Gerbig, Christoph; -Thomas Koch, Frank

2013-04-01

Long term observations of atmospheric greenhouse gas measuring stations, located at representative regions over the continent, improve our understanding of greenhouse gas sources and sinks. These mixing ratio measurements can be linked to surface fluxes by atmospheric transport inversions. Within the upcoming years new stations are to be deployed, which requires decision making tools with respect to the location and the density of the network. We are developing a method to assess potential greenhouse gas observing networks in terms of their ability to recover specific target quantities. As target quantities we use CO2 fluxes aggregated to specific spatial and temporal scales. We introduce a high resolution inverse modeling framework, which attempts to combine advantages from pixel based inversions with those of a carbon cycle data assimilation system (CCDAS). The hybrid inversion system consists of the Lagrangian transport model STILT, the diagnostic biosphere model VPRM and a Bayesian inversion scheme. We aim to retrieve the spatiotemporal distribution of net ecosystem exchange (NEE) at a high spatial resolution (10 km x 10 km) by inverting for spatially and temporally varying scaling factors for gross ecosystem exchange (GEE) and respiration (R) rather than solving for the fluxes themselves. Thus the state space includes parameters for controlling photosynthesis and respiration, but unlike in a CCDAS it allows for spatial and temporal variations, which can be expressed as NEE(x,y,t) = λG(x,y,t) GEE(x,y,t) + λR(x,y,t) R(x,y,t) . We apply spatially and temporally correlated uncertainties by using error covariance matrices with non-zero off-diagonal elements. Synthetic experiments will test our system and select the optimal a priori error covariance by using different spatial and temporal correlation lengths on the error statistics of the a priori covariance and comparing the optimized fluxes against the 'known truth'. As 'known truth' we use independent fluxes

CO2 fluxes near a forest edge

DEFF Research Database (Denmark)

Sogachev, Andrey; Leclerc, Monique Y.; Zhang, Gensheng

2008-01-01

In contrast with recent advances on the dynamics of the flow at a forest edge, few studies have considered its role on scalar transport and, in particular, on CO2 transfer. The present study addresses the influence of the abrupt roughness change on forest atmosphere CO2 exchange and contrasts...... as a function of both sources/sinks distribution and the vertical structure of the canopy. Results suggest that the ground source plays a major role in the formation of wave-like vertical CO2 flux behavior downwind of a forest edge, despite the fact that the contribution of foliage sources/sinks changes...

Seasonal soil CO2 flux under big sagebrush (Artemisia tridentata Nutt.)

Science.gov (United States)

Michael C. Amacher; Cheryl L. Mackowiak

2011-01-01

Soil respiration is a major contributor to atmospheric CO2, but accurate landscape-scale estimates of soil CO2 flux for many ecosystems including shrublands have yet to be established. We began a project to measure, with high spatial and temporal resolution, soil CO2 flux in a stand (11 x 25 m area) of big sagebrush (Artemisia tridentata Nutt.) at the Logan, Utah,...

Diurnal and Seasonal Variations of Eddy-Covariance Carbon Dioxide Fluxes Above an Urban Wetland, Partitioned by Vegetation Cover

Science.gov (United States)

Schafer, K. V.; Duman, T.

2017-12-01

The New Jersey Meadowlands are an urban brackish marsh with a long history of human activity causing disturbances and alterations. Carbon emissions were measured from two sites in the Meadowlands, a natural site and a restored site, using eddy-covariance (EC) from 2014 to 2016. At each site, the EC towers were placed at the interface of two vegetation covers, allowing capturing this aspect of the wetland's heterogeneity. Using footprint modeling and light response curves we were able to partition measured fluxes between vegetation cover types and compare CO2 fluxes from patches of invasive versus native wetland vegetation communities. We show that further separating the data into seasonal and diurnal fluxes reveals patterns in CO2 fluxes that allow determining the nature of each vegetation cover as a source or sink for CO2. Our results also show that CO2 emissions from the restored wetland are significantly higher than the natural wetland. Areas of invasive Phragmites australis at the natural site had the lowest CO2 release rates during winter. These were consistently lower in magnitude than summer daytime uptake, therefore making this part of the wetland a CO2 sink. Areas planted with native Spartina alterniflora at the restored site had the largest uptake during daytime, therefore seemingly justifying restoration activities. However, they also had the highest emission rates during summer nighttime, and therefore the daily summer net uptake was not the highest compared with other vegetation covers. Furthermore, emissions from the restored site during winter were larger compared to the natural site, indicating that restoration activities might have led to a significant increase of carbon release from the wetland. Thus, during the study period the restored wetland acted as a carbon source.

Net ecosystem exchange and energy fluxes measured with the eddy covariance technique in a western Siberian bog

Directory of Open Access Journals (Sweden)

P. Alekseychik

2017-08-01

Full Text Available Very few studies of ecosystem–atmosphere exchange involving eddy covariance data have been conducted in Siberia, with none in the western Siberian middle taiga. This work provides the first estimates of carbon dioxide (CO2 and energy budgets in a typical bog of the western Siberian middle taiga based on May–August measurements in 2015. The footprint of measured fluxes consisted of a homogeneous mixture of tree-covered ridges and hollows with the vegetation represented by typical sedges and shrubs. Generally, the surface exchange rates resembled those of pine-covered bogs elsewhere. The surface energy balance closure approached 100 %. Net CO2 uptake was comparatively high, summing up to 202 gC m−2 for the four measurement months, while the Bowen ratio was seasonally stable at 28 %. The ecosystem turned into a net CO2 source during several front passage events in June and July. The periods of heavy rain helped keep the water table at a sustainably high level, preventing a usual drawdown in summer. However, because of the cloudy and rainy weather, the observed fluxes might rather represent the special weather conditions of 2015 than their typical magnitudes.

Grain Yield Observations Constrain Cropland CO2 Fluxes Over Europe

Science.gov (United States)

Combe, M.; de Wit, A. J. W.; Vilà-Guerau de Arellano, J.; van der Molen, M. K.; Magliulo, V.; Peters, W.

2017-12-01

Carbon exchange over croplands plays an important role in the European carbon cycle over daily to seasonal time scales. A better description of this exchange in terrestrial biosphere models—most of which currently treat crops as unmanaged grasslands—is needed to improve atmospheric CO2 simulations. In the framework we present here, we model gross European cropland CO2 fluxes with a crop growth model constrained by grain yield observations. Our approach follows a two-step procedure. In the first step, we calculate day-to-day crop carbon fluxes and pools with the WOrld FOod STudies (WOFOST) model. A scaling factor of crop growth is optimized regionally by minimizing the final grain carbon pool difference to crop yield observations from the Statistical Office of the European Union. In a second step, we re-run our WOFOST model for the full European 25 × 25 km gridded domain using the optimized scaling factors. We combine our optimized crop CO2 fluxes with a simple soil respiration model to obtain the net cropland CO2 exchange. We assess our model's ability to represent cropland CO2 exchange using 40 years of observations at seven European FluxNet sites and compare it with carbon fluxes produced by a typical terrestrial biosphere model. We conclude that our new model framework provides a more realistic and strongly observation-driven estimate of carbon exchange over European croplands. Its products will be made available to the scientific community through the ICOS Carbon Portal and serve as a new cropland component in the CarbonTracker Europe inverse model.

BOREAS TF-3 Automated Chamber CO2 Flux Data from the NSA-OBS

Science.gov (United States)

Goulden, Michael L.; Crill, Patrick M.; Hall, Forrest G. (Editor); Conrad, Sara (Editor)

2000-01-01

The BOReal Ecosystem Atmosphere Study Tower Flux (BOREAS TF-3) and Trace Gas Biogeochemistry (TGB-1) teams collected automated CO2 chamber flux data in their efforts to fully describe the CO2 flux at the Northern Study Area-Old Black Spruce (NSA-OBS) site. This data set contains fluxes of CO2 at the NSA-OBS site measured using automated chambers. In addition to reporting the CO2 flux, it reports chamber air temperature, moss temperature, and light levels during each measurement. The data set covers the period from 23-Sep-1995 through 26-Oct-1995 and from 28-May-1996 through 21-Oct-1996. The data are stored in tabular ASCII files.

Agricultural crops and soil treatment impacts on the daily and seasonal dynamics of CO2 fluxes in the field agroecosystems at the Central region of Russia

Science.gov (United States)

Mazirov, Ilya; Vasenev, Ivan; Meshalkina, Joulia; Yaroslavtsev, Alexis; Berezovskiy, Egor; Djancharov, Turmusbek

2015-04-01

The problem of greenhouse gases' concentrations increasing becomes more and more important due to global changes issues. The main component of greenhouse gases is carbon dioxide. The researches focused on its fluxes in natural and anthropogenic modified landscapes can help in this problem solution. Our research has been done with support of the RF Government grants # 11.G34.31.0079 and # 14.120.14.4266 and of FP7 Grant # 603542 LUC4C in the representative for Central Region of Russia field agroecosystems at the Precision Farming Experimental Field of Russian Timiryazev State Agrarian University with cultivated sod podzoluvisols, barley and oats - vetch grass mix (Moscow station of the RusFluxNet). The daily and seasonal dynamics of the carbon dioxide have been studied at the ecosystem level by the Eddy covariance method (2 stations) and at the soil level by the exposition chamber method (40 chambers) with mobile infra red gas analyzer (Li-Cor 820). The primary Eddy covariance monitoring data on CO2 fluxes and water vapor have been processed by EddyPro software developed by LI-COR Biosciences. According to the two-year monitoring data the daily CO2 sink during the vegetation season is usually approximately two times higher than its emission at night. Seasonal CO2 fluxes comparative stabilization has been fixed in case the plants height around 10-12 cm and it usually persist until the wax ripeness phase. There is strong dependence between the soil CO2 emission and the air temperature with the correlation coefficient 0.86 in average (due to strong input of the soil thin top functional subhorizon), but it drops essentially at the end of the season - till 0.38. The soil moisture impact on CO2 fluxes dynamics was less, with negative correlation at the end of the season. High daily dynamics of CO2 fluxes determines the protocol requirements for seasonal soil monitoring investigation with less limitation at the end of the season. The accumulated monitoring data will be

The Impact of Prior Biosphere Models in the Inversion of Global Terrestrial CO2 Fluxes by Assimilating OCO-2 Retrievals

Science.gov (United States)

Philip, Sajeev; Johnson, Matthew S.

2018-01-01

Atmospheric mixing ratios of carbon dioxide (CO2) are largely controlled by anthropogenic emissions and biospheric fluxes. The processes controlling terrestrial biosphere-atmosphere carbon exchange are currently not fully understood, resulting in terrestrial biospheric models having significant differences in the quantification of biospheric CO2 fluxes. Atmospheric transport models assimilating measured (in situ or space-borne) CO2 concentrations to estimate "top-down" fluxes, generally use these biospheric CO2 fluxes as a priori information. Most of the flux inversion estimates result in substantially different spatio-temporal posteriori estimates of regional and global biospheric CO2 fluxes. The Orbiting Carbon Observatory 2 (OCO-2) satellite mission dedicated to accurately measure column CO2 (XCO2) allows for an improved understanding of global biospheric CO2 fluxes. OCO-2 provides much-needed CO2 observations in data-limited regions facilitating better global and regional estimates of "top-down" CO2 fluxes through inversion model simulations. The specific objectives of our research are to: 1) conduct GEOS-Chem 4D-Var assimilation of OCO-2 observations, using several state-of-the-science biospheric CO2 flux models as a priori information, to better constrain terrestrial CO2 fluxes, and 2) quantify the impact of different biospheric model prior fluxes on OCO-2-assimilated a posteriori CO2 flux estimates. Here we present our assessment of the importance of these a priori fluxes by conducting Observing System Simulation Experiments (OSSE) using simulated OCO-2 observations with known "true" fluxes.

Assessing the Importance of Prior Biospheric Fluxes on Inverse Model Estimates of CO2

Science.gov (United States)

Philip, S.; Johnson, M. S.; Potter, C. S.; Genovese, V. B.

2017-12-01

Atmospheric mixing ratios of carbon dioxide (CO2) are largely controlled by anthropogenic emissions and biospheric sources/sinks. The processes controlling terrestrial biosphere-atmosphere carbon exchange are currently not fully understood, resulting in models having significant differences in the quantification of biospheric CO2 fluxes. Currently, atmospheric chemical transport models (CTM) and global climate models (GCM) use multiple different biospheric CO2 flux models resulting in large differences in simulating the global carbon cycle. The Orbiting Carbon Observatory 2 (OCO-2) satellite mission was designed to allow for the improved understanding of the processes involved in the exchange of carbon between terrestrial ecosystems and the atmosphere, and therefore allowing for more accurate assessment of the seasonal/inter-annual variability of CO2. OCO-2 provides much-needed CO2 observations in data-limited regions allowing for the evaluation of model simulations of greenhouse gases (GHG) and facilitating global/regional estimates of "top-down" CO2 fluxes. We conduct a 4-D Variation (4D-Var) data assimilation with the GEOS-Chem (Goddard Earth Observation System-Chemistry) CTM using 1) OCO-2 land nadir and land glint retrievals and 2) global in situ surface flask observations to constrain biospheric CO2 fluxes. We apply different state-of-the-science year-specific CO2 flux models (e.g., NASA-CASA (NASA-Carnegie Ames Stanford Approach), CASA-GFED (Global Fire Emissions Database), Simple Biosphere Model version 4 (SiB-4), and LPJ (Lund-Postdam-Jena)) to assess the impact of "a priori" flux predictions to "a posteriori" estimates. We will present the "top-down" CO2 flux estimates for the year 2015 using OCO-2 and in situ observations, and a complete indirect evaluation of the a priori and a posteriori flux estimates using independent in situ observations. We will also present our assessment of the variability of "top-down" CO2 flux estimates when using different

Storage flux uncertainty impact on eddy covariance net ecosystem exchange measurements

Science.gov (United States)

Nicolini, Giacomo; Aubinet, Marc; Feigenwinter, Christian; Heinesch, Bernard; Lindroth, Anders; Mamadou, Ossénatou; Moderow, Uta; Mölder, Meelis; Montagnani, Leonardo; Rebmann, Corinna; Papale, Dario

2017-04-01

Complying with several assumption and simplifications, most of the carbon budget studies based on eddy covariance (EC) measurements, quantify the net ecosystem exchange (NEE) by summing the flux obtained by EC (Fc) and the storage flux (Sc). Sc is the rate of change of CO2, within the so called control volume below the EC measurement level, given by the difference in the instantaneous profiles of concentration at the beginning and end of the EC averaging period, divided by the averaging period. While cumulating over time led to a nullification of Sc, it can be significant at short time periods. The approaches used to estimate Sc fluxes largely vary, from measurements based only on a single sampling point (usually located at the EC measurement height) to measurements based on several sampling profiles distributed within the control volume. Furthermore, the number of sampling points within each profile vary, according to their height and the ecosystem typology. It follows that measurement accuracy increases with the sampling intensity within the control volume. In this work we use the experimental dataset collected during the ADVEX campaign in which Sc flux has been measured in three similar forest sites by the use of 5 sampling profiles (towers). Our main objective is to quantify the impact of Sc measurement uncertainty on NEE estimates. Results show that different methods may produce substantially different Sc flux estimates, with problematic consequences in case high frequency (half-hourly) data are needed for the analysis. However, the uncertainty on long-term estimates may be tolerate.

[Periodic characteristics of soil CO2 flux in mangrove wetland of Quanzhou Bay, China].

Science.gov (United States)

Wang, Zong-Lin; Wu, Yan-You; Xing, De-Ke; Liu, Rong-Cheng; Zhou Gui-Yao; Zhao, Kuan

2014-09-01

Mangrove wetland ecosystem in Quanzhou Bay in Fujian Province is newly restored with a regular semidiurnal tide. Soil CO2 concentration in the mangrove soil was determined by Li-840 portable gas analyzer, and periodic characteristics of soil CO2 emission was investigated. The soil CO2 flux in the wetland soil was relatively small because the mangrove was young. The change trends of soil CO2 concentration and flux with time were consistent in Kandelia obovate and Aegiceras corniculatum communities in the intertidal periods. The CO2 concentration and flux in the wetland soil were 557.08-2211.50 μmol · mol(-1) and -0.21-0.40 μmol · m(-2) · s(-1), respectively. The average CO2 flux in the wetland soil was 0.26 μmol · mol(-1) · s(-1) in the intertidal of morning and evening tides (early intertidal) and -0.01 μmol · m(-2) · s(-1) in the intertidal of evening and morning tides (late intertidal), respectively. At the same time after the tide, the concentration and flux of CO2 in the mangrove soil in early intertidal was higher than that in late intertidal. In early intertidal, the relationship between the flux and instantaneous concentration of CO2 in the wetland soil was expressed as a bell-shaped curve, and CO2 flux increased first and then decreased with the increasing CO2 concentration, which was in conformity with Gaussian distribution.

Increasing CO2 flux at Pisciarelli, Campi Flegrei, Italy

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M. Queißer

2017-09-01

Full Text Available The Campi Flegrei caldera is located in the metropolitan area of Naples (Italy and has been undergoing different stages of unrest since 1950, evidenced by episodes of significant ground uplift followed by minor subsidence, increasing and fluctuating emission strengths of water vapor and CO2 from fumaroles, and periodic seismic crises. We deployed a scanning laser remote-sensing spectrometer (LARSS that measured path-integrated CO2 concentrations in the Pisciarelli area in May 2017. The resulting mean CO2 flux is 578 ± 246 t d−1. Our data suggest a significant increase in CO2 flux at this site since 2015. Together with recent geophysical observations, this suggests a greater contribution of the magmatic source to the degassing and/or an increase in permeability at shallow levels. Thanks to the integrated path soundings, LARSS may help to give representative measurements from large regions containing different CO2 sources, including fumaroles, low-temperature vents, and degassing soils, helping to constrain the contribution of deep gases and their migration mechanisms towards the surface.

Suitability of quantum cascade laser spectroscopy for CH4 and N2O eddy covariance flux measurements

Directory of Open Access Journals (Sweden)

A. T. Vermeulen

2007-08-01

Full Text Available A quantum cascade laser spectrometer was evaluated for eddy covariance flux measurements of CH4 and N2O using three months of continuous measurements at a field site. The required criteria for eddy covariance flux measurements including continuity, sampling frequency, precision and stationarity were examined. The system operated continuously at a dairy farm on peat grassland in the Netherlands from 17 August to 6 November 2006. An automatic liquid nitrogen filling system for the infrared detector was employed to provide unattended operation of the system. The electronic sampling frequency was 10 Hz, however, the flow response time was 0.08 s, which corresponds to a bandwidth of 2 Hz. A precision of 2.9 and 0.5 ppb Hz−1/2 was obtained for CH4 and N2O, respectively. Accuracy was assured by frequent calibrations using low and high standard additions. Drifts in the system were compensated by using a 120 s running mean filter. The average CH4 and N2O exchange was 512 ngC m−2 s−1 (2.46 mg m−2 hr−1 and 52 ngN m−2 s−1 (0.29 mg m−2 hr−1. Given that 40% of the total N2O emission was due to a fertilizing event.

Component greenhouse gas fluxes and radiative balance from two deltaic marshes in Louisiana: Pairing chamber techniques and eddy covariance

Science.gov (United States)

Krauss, Ken W.; Holm, Guerry O.; Perez, Brian C.; McWhorter, David E.; Cormier, Nicole; Moss, Rebecca; Johnson, Darren; Neubauer, Scott C; Raynie, Richard C

2016-01-01

Coastal marshes take up atmospheric CO2 while emitting CO2, CH4, and N2O. This ability to sequester carbon (C) is much greater for wetlands on a per-area basis than from most ecosystems, facilitating scientific, political, and economic interest in their value as greenhouse gas sinks. However, the greenhouse gas balance of Gulf of Mexico wetlands is particularly understudied. We describe the net ecosystem exchange (NEEc) of CO2 and CH4 using eddy covariance (EC) in comparison with fluxes of CO2, CH4, and N2O using chambers from brackish and freshwater marshes in Louisiana, USA. From EC, we found that 182 g C m-2 y-1 was lost through NEEc from the brackish marsh. Of this, 11 g C m-2 y-1 resulted from net CH4 emissions and the remaining 171 g C m-2 y-1 resulted from net CO2 emissions. In contrast, -290 g C m2 y-1 was taken up through NEEc by the freshwater marsh, with 47 g C m-2 y-1 emitted as CH4 and -337 g C m-2 y-1 taken up as CO2. From chambers, we discovered that neither site had large fluxes of N2O. Sustained-flux greenhouse gas accounting metrics indicated that both marshes had a positive (warming) radiative balance, with the brackish marsh having a substantially greater warming effect than the freshwater marsh. That net respiratory emissions of CO2 and CH4 as estimated through chamber techniques were 2-4 times different from emissions estimated through EC requires additional understanding of the artifacts created by different spatial and temporal sampling footprints between techniques.

Recent global CO2 flux inferred from atmospheric CO2 observations and its regional analyses

Directory of Open Access Journals (Sweden)

J. M. Chen

2011-11-01

Full Text Available The net surface exchange of CO2 for the years 2002–2007 is inferred from 12 181 atmospheric CO2 concentration data with a time-dependent Bayesian synthesis inversion scheme. Monthly CO2 fluxes are optimized for 30 regions of the North America and 20 regions for the rest of the globe. Although there have been many previous multiyear inversion studies, the reliability of atmospheric inversion techniques has not yet been systematically evaluated for quantifying regional interannual variability in the carbon cycle. In this study, the global interannual variability of the CO2 flux is found to be dominated by terrestrial ecosystems, particularly by tropical land, and the variations of regional terrestrial carbon fluxes are closely related to climate variations. These interannual variations are mostly caused by abnormal meteorological conditions in a few months in the year or part of a growing season and cannot be well represented using annual means, suggesting that we should pay attention to finer temporal climate variations in ecosystem modeling. We find that, excluding fossil fuel and biomass burning emissions, terrestrial ecosystems and oceans absorb an average of 3.63 ± 0.49 and 1.94 ± 0.41 Pg C yr−1, respectively. The terrestrial uptake is mainly in northern land while the tropical and southern lands contribute 0.62 ± 0.47, and 0.67 ± 0.34 Pg C yr−1 to the sink, respectively. In North America, terrestrial ecosystems absorb 0.89 ± 0.18 Pg C yr−1 on average with a strong flux density found in the south-east of the continent.

Uncertainty of long-term CO2 flux estimates due to the choice of the spectral correction method

Science.gov (United States)

Ibrom, Andreas; Geißler, Simon; Pilegaard, Kim

2010-05-01

The eddy covariance system at the Danish beech forest long-term flux observation site at Sorø has been intensively examined. Here we investigate which systematic and non-systematic effects the choice of the spectral correction method has on long-term net CO2 flux estimates and their components. Ibrom et al. (2007) gave an overview over different ways to correct for low-pass filtering of the atmospheric turbulent signal by a closed path eddy covariance system. They used degraded temperature time series for spectral correction of low-pass filtered signals. In this new study, correction for high-pass filtering was also included, which made it anyway necessary to use model co-spectra. We compared different ways of adapting different kinds of model co-spectra to the wealth of 14 years high frequency raw data. As the trees grew, the distance between the sonic anemometer and the displacement height decreased over time. The study enabled us to compare the two approaches and different variants of them to give recommendations on their use. The analysis showed that model spectra should not be derived from co-spectra between the vertical wind speed (w) and the scalars measured with the closed path system, i.e. CO2 and H20 concentrations, but instead with sonic temperature (T) w cospectra, to avoid low-pass filtering effects on the estimation of the co-spectral peak frequency (fx). This concern was already expressed earlier in the above mentioned study, but here we show the quantitative effects. The wT co-spectra did not show any height effect on fx as it was suggested in generally used parameterizations. A possible reason for this difference is that measurements, like in all forest flux sites, took place in the roughness sub-layer and not in the inertial sub-layer. At the same time the shape of the relationship between fx and the stability parameter ? differed much from that of often used parameterizations (e.g. from Horst, 1997). The shift of fx towards higher frequencies at

SOIL FLUXES OF CO2, CO, NO AND N2O FROM AN OLD-PASTURE AND FROM NATIVE SAVANNA IN BRAZIL

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We compared fluxes of CO2, CO, NO and N2O, soil microbial biomass, and N-mineralization rates in a 20-year old Brachiaria pasture and a native cerrado area (savanna in Central Brazil). In order to assess the spatial variability of CO2 fluxes, we tested the relation between elect...

Impact of water use efficiency on eddy covariance flux partitioning using correlation structure analysis

Science.gov (United States)

Anderson, Ray; Skaggs, Todd; Alfieri, Joseph; Kustas, William; Wang, Dong; Ayars, James

2016-04-01

Partitioned land surfaces fluxes (e.g. evaporation, transpiration, photosynthesis, and ecosystem respiration) are needed as input, calibration, and validation data for numerous hydrological and land surface models. However, one of the most commonly used techniques for measuring land surface fluxes, Eddy Covariance (EC), can directly measure net, combined water and carbon fluxes (evapotranspiration and net ecosystem exchange/productivity). Analysis of the correlation structure of high frequency EC time series (hereafter flux partitioning or FP) has been proposed to directly partition net EC fluxes into their constituent components using leaf-level water use efficiency (WUE) data to separate stomatal and non-stomatal transport processes. FP has significant logistical and spatial representativeness advantages over other partitioning approaches (e.g. isotopic fluxes, sap flow, microlysimeters), but the performance of the FP algorithm is reliant on the accuracy of the intercellular CO2 (ci) concentration used to parameterize WUE for each flux averaging interval. In this study, we tested several parameterizations for ci as a function of atmospheric CO2 (ca), including (1) a constant ci/ca ratio for C3 and C4 photosynthetic pathway plants, (2) species-specific ci/ca-Vapor Pressure Deficit (VPD) relationships (quadratic and linear), and (3) generalized C3 and C4 photosynthetic pathway ci/ca-VPD relationships. We tested these ci parameterizations at three agricultural EC towers from 2011-present in C4 and C3 crops (sugarcane - Saccharum officinarum L. and peach - Prunus persica), and validated again sap-flow sensors installed at the peach site. The peach results show that the species-specific parameterizations driven FP algorithm came to convergence significantly more frequently (~20% more frequently) than the constant ci/ca ratio or generic C3-VPD relationship. The FP algorithm parameterizations with a generic VPD relationship also had slightly higher transpiration (5 Wm-2

Grazing effects on ecosystem CO2 fluxes differ among temperate steppe types in Eurasia.

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Hou, Longyu; Liu, Yan; Du, Jiancai; Wang, Mingya; Wang, Hui; Mao, Peisheng

2016-07-01

Grassland ecosystems play a critical role in regulating CO2 fluxes into and out of the Earth's surface. Whereas previous studies have often addressed single fluxes of CO2 separately, few have addressed the relation among and controls of multiple CO2 sub-fluxes simultaneously. In this study, we examined the relation among and controls of individual CO2 fluxes (i.e., GEP, NEP, SR, ER, CR) in three contrasting temperate steppes of north China, as affected by livestock grazing. Our findings show that climatic controls of the seasonal patterns in CO2 fluxes were both individual flux- and steppe type-specific, with significant grazing impacts observed for canopy respiration only. In contrast, climatic controls of the annual patterns were only individual flux-specific, with minor grazing impacts on the individual fluxes. Grazing significantly reduced the mean annual soil respiration rate in the typical and desert steppes, but significantly enhanced both soil and canopy respiration in the meadow steppe. Our study suggests that a reassessment of the role of livestock grazing in regulating GHG exchanges is imperative in future studies.

Quantification of surface energy fluxes from a small water body using scintillometry and eddy covariance

DEFF Research Database (Denmark)

McGloin, Ryan; McGowan, Hamish; McJannet, David

2014-01-01

Accurate quantification of evaporation from small water storages is essential for water management and planning, particularly in water-scarce regions. In order to ascertain suitable methods for direct measurement of evaporation from small water bodies, this study presents a comparison of eddy......% greater than eddy covariance measurements. We suggest possible reasons for this difference and provide recommendations for further research for improving measurements of surface energy fluxes over small water bodies using eddy covariance and scintillometry. Key Points Source areas for Eddy covariance...... and scintillometry were on the water surface Reasonable agreement was shown between the sensible heat flux measurements Scintillometer estimates of latent heat flux were greater than eddy covariance...

A New Tool for Automated Data Collection and Complete On-site Flux Data Processing for Eddy Covariance Measurements

Science.gov (United States)

Begashaw, I. G.; Kathilankal, J. C.; Li, J.; Beaty, K.; Ediger, K.; Forgione, A.; Fratini, G.; Johnson, D.; Velgersdyk, M.; Hupp, J. R.; Xu, L.; Burba, G. G.

2014-12-01

The eddy covariance method is widely used for direct measurements of turbulent exchange of gases and energy between the surface and atmosphere. In the past, raw data were collected first in the field and then processed back in the laboratory to achieve fully corrected publication-ready flux results. This post-processing consumed significant amount of time and resources, and precluded researchers from accessing near real-time final flux results. A new automated measurement system with novel hardware and software designs was developed, tested, and deployed starting late 2013. The major advancements with this automated flux system include: 1) Enabling logging high-frequency, three-dimensional wind speeds and multiple gas densities (CO2, H2O and CH4), low-frequency meteorological data, and site metadata simultaneously through a specially designed file format 2) Conducting fully corrected, real-time on-site flux computations using conventional as well as user-specified methods, by implementing EddyPro Software on a small low-power microprocessor 3) Providing precision clock control and coordinate information for data synchronization and inter-site data comparison by incorporating a GPS and Precision Time Protocol. Along with these innovations, a data management server application was also developed to chart fully corrected real-time fluxes to assist remote system monitoring, to send e-mail alerts, and to automate data QA/QC, transfer and archiving at individual stations or on a network level. Combination of all of these functions was designed to help save substantial amount of time and costs associated with managing a research site by eliminating the post-field data processing, reducing user errors and facilitating real-time access to fully corrected flux results. The design, functionality, and test results from this new eddy covariance measurement tool will be presented.

Terrestrial gross carbon dioxide uptake : Global distribution and covariation with climate

NARCIS (Netherlands)

Beer, Christian; Reichstein, Markus; Tomelleri, Enrico; Ciais, Philippe; Jung, Martin; Carvalhais, Nuno; Rödenbeck, Christian; Arain, M. Altaf; Baldocchi, Dennis D.; Bonan, Gordon B.; Bondeau, Alberte; Cescatti, Alessandro; Lasslop, Gitta; Lindroth, Anders; Lomas, Mark; Luyssaert, Sebastiaan; Margolis, Hank; Oleson, Keith W.; Roupsard, Olivier; Veenendaal, Elmar; Viovy, Nicolas; Williams, Christopher M.; Woodward, F. Ian; Papale, Dario

2010-01-01

Terrestrial gross primary production (GPP) is the largest global CO 2 flux driving several ecosystem functions. We provide an observation-based estimate of this flux at 123 ± 8 petagrams of carbon per year (Pg C year-1) using eddy covariance flux data and various diagnostic models. Tropical forests

Soil CO2 flux from three ecosystems in tropical peatland of Sarawak, Malaysia

International Nuclear Information System (INIS)

Melling, Lulie; Hatano, Ryusuke

2005-01-01

Soil CO 2 flux was measured monthly over a year from tropical peatland of Sarawak, Malaysia using a closed-chamber technique. The soil CO 2 flux ranged from 100 to 533 mg C/m 2 /h for the forest ecosystem, 63 to 245 mg C/m 2 /h for the sago and 46 to 335 mg C/m 2 /h for the oil palm. Based on principal component analysis (PCA), the environmental variables over all sites could be classified into three components, namely, climate, soil moisture and soil bulk density, which accounted for 86% of the seasonal variability. A regression tree approach showed that CO 2 flux in each ecosystem was related to different underlying environmental factors. They were relative humidity for forest, soil temperature at 5 cm for sago and water-filled pore space for oil palm. On an annual basis, the soil CO 2 flux was highest in the forest ecosystem with an estimated production of 2.1 kg C/m 2 /yr followed by oil palm at 1.5 kg C/m 2 /yr and sago at 1.1 kg C/m 2 /yr. The different dominant controlling factors in CO 2 flux among the studied ecosystems suggested that land use affected the exchange of CO 2 between tropical peatland and the atmosphere

Comparison of ecosystem water flux measured with the Eddy covariance- and the direct xylem sap flux method in a mountainous forest

Energy Technology Data Exchange (ETDEWEB)

Stefanicki, G; Geissbuehler, P; Siegwolf, R [Paul Scherrer Inst. (PSI), Villigen (Switzerland)

1999-08-01

The Eddy covariance technique allows to measure different components of turbulent air fluxes, including the flow of water vapour. Sap flux measurements determine directly the water flow in tree stems. We compared the water flux just above the crowns of trees in a forest by the technique of Eddy covariance and the water flux by the xylem sap flux method. These two completely different approaches showed a good qualitative correspondence. The correlation coefficient is 0.8. With an estimation of the crown diameter of the measured tree we also find a very good quantitative agreement. (author) 3 figs., 5 refs.

Year-round Regional CO2 Fluxes from Boreal and Tundra Ecosystems in Alaska

Science.gov (United States)

Commane, R.; Lindaas, J.; Benmergui, J. S.; Luus, K. A.; Chang, R. Y. W.; Daube, B. C.; Euskirchen, E. S.; Henderson, J.; Karion, A.; Miller, J. B.; Miller, S. M.; Parazoo, N.; Randerson, J. T.; Sweeney, C.; Tans, P. P.; Thoning, K. W.; Veraverbeke, S.; Miller, C. E.; Wofsy, S. C.

2016-12-01

High-latitude ecosystems could release large amounts of carbon dioxide (CO2) to the atmosphere in a warmer climate. We derive temporally and spatially resolved year-round CO2 fluxes in Alaska from a synthesis of airborne and tower CO2 observations in 2012-2014. We find that tundra ecosystems were net sources of atmospheric CO2. We discuss these flux estimates in the context of long-term CO2 measurements at Barrow, AK, to asses the long term trend in carbon fluxes in the Arctic. Many Earth System Models incorrectly simulate net carbon uptake in Alaska presently. Our results imply that annual net emission of CO2 to the atmosphere may have increased markedly in this region of the Arctic in response to warming climate, supporting the view that climate-carbon feedback is strongly positive in the high Arctic.

Soil CO2 flux baseline in an urban monogenetic volcanic field: the Auckland Volcanic Field, New Zealand

Science.gov (United States)

Mazot, Agnès; Smid, Elaine R.; Schwendenmann, Luitgard; Delgado-Granados, Hugo; Lindsay, Jan

2013-11-01

The Auckland Volcanic Field (AVF) is a dormant monogenetic basaltic field located in Auckland, New Zealand. Though soil gas CO2 fluxes are routinely used to monitor volcanic regions, there have been no published studies of soil CO2 flux or soil gas CO2 concentrations in the AVF to date or many other monogenetic fields worldwide. We measured soil gas CO2 fluxes and soil gas CO2 concentrations in 2010 and 2012 in varying settings, seasons, and times of day to establish a baseline soil CO2 flux and to determine the major sources of and controlling influences on Auckland's soil CO2 flux. Soil CO2 flux measurements varied from 0 to 203 g m-2 day-1, with an average of 27.1 g m-2 day-1. Higher fluxes were attributed to varying land use properties (e.g., landfill). Using a graphical statistical approach, two populations of CO2 fluxes were identified. Isotope analyses of δ13CO2 confirmed that the source of CO2 in the AVF is biogenic with no volcanic component. These data may be used to assist with eruption forecasting in the event of precursory activity in the AVF, and highlight the importance of knowing land use history when assessing soil gas CO2 fluxes in urban environments.

APO observations in Southern Greenland: evaluation of modelled air-sea O2 and CO2 fluxes

Science.gov (United States)

Bonne, Jean-Louis; Bopp, Laurent; Delmotte, Marc; Cadule, Patricia; Resplandy, Laure; Nevison, Cynthia; Manizza, Manfredi; Valentin Lavric, Jost; Manning, Andrew C.; Masson-Delmotte, Valérie

2014-05-01

Since September 2007, the atmospheric CO2 mole fraction and O2/N2 ratio (a proxy for O2 concentration) have been monitored continuously at the coastal site of Ivittuut, southern Greenland (61.21° N, 48.17° W). From 2007 to 2013, our measurements show multi-annual trends of +2.0 ppm/year and -20 per meg/year respectively for CO2 and O2/N2, with annual average peak-to-peak seasonal amplitudes of 14+/-1 ppm and 130+/-15 per meg. We investigate the implications of our data set in terms of APO (Atmospheric Potential Oxygen). This tracer, obtained by a linear combination of CO2 and O2/N2 data, is invariant to CO2 and O2 exchanges in the land biota, but sensitive to the oceanic component of the O2 cycle. It is used as a bridge to evaluate air-sea CO2 and O2 fluxes from atmospheric variations of CO2 and O2/N2. Global ocean biogeochemical models produce estimates of CO2 and O2 air-sea fluxes. Atmospheric APO variations can be simulated through transportation of these fluxes in the atmosphere by Eulerian transport models. Thus, model values of atmospheric APO can be extracted at the station location. This study is based on air-sea flux outputs from CMIP5 simulations. After atmospheric transportation, they give access to atmospheric APO climatologies which can be compared, in terms of seasonal cycles and inter-annual variability, to the in situ observations. A preliminary study is based on the CCSM ocean model air-sea fluxes transported in the atmosphere with the MATCH transport model, over the period 1979-2004. The amplitude of the APO seasonal cycle is correctly captured, but year to year variations on this seasonal cycle appears to be underestimated compared to observations. The LMDZ atmospheric transport model is also used to transport the ocean fluxes from five CMIP5 models, over the period 1979-2005, showing different amplitudes and timings of APO seasonal cycles. This methodology is a first step to evaluate the origin of observed APO variations at our site and then

Importance of crop varieties and management practices: evaluation of a process-based model for simulating CO2 and H2O fluxes at five European maize (Zea mays L.) sites

Science.gov (United States)

Li, L.; Vuichard, N.; Viovy, N.; Ciais, P.; Wang, T.; Ceschia, E.; Jans, W.; Wattenbach, M.; Béziat, P.; Gruenwald, T.; Lehuger, S.; Bernhofer, C.

2011-06-01

This paper is a modelling study of crop management impacts on carbon and water fluxes at a range of European sites. The model is a crop growth model (STICS) coupled with a process-based land surface model (ORCHIDEE). The data are online eddy-covariance observations of CO2 and H2O fluxes at five European maize cultivation sites. The results show that the ORCHIDEE-STICS model explains up to 75 % of the observed daily net CO2 ecosystem exchange (NEE) variance, and up to 79 % of the latent heat flux (LE) variance at five sites. The model is better able to reproduce gross primary production (GPP) variations than terrestrial ecosystem respiration (TER) variations. We conclude that structural deficiencies in the model parameterizations of leaf area index (LAI) and TER are the main sources of error in simulating CO2 and H2O fluxes. A number of sensitivity tests, with variable crop variety, nitrogen fertilization, irrigation, and planting date, indicate that any of these management factors is able to change NEE by more than 15 %, but that the response of NEE to management parameters is highly site-dependent. Changes in management parameters are found to impact not only the daily values of NEE and LE, but also the cumulative yearly values. In addition, LE is shown to be less sensitive to management parameters than NEE. Multi-site model evaluations, coupled with sensitivity analysis to management parameters, thus provide important information about model errors, which helps to improve the simulation of CO2 and H2O fluxes across European croplands.

CO2 volume fluxes outgassing from champagne glasses: the impact of champagne ageing.

Science.gov (United States)

Liger-Belair, Gérard; Villaume, Sandra; Cilindre, Clara; Jeandet, Philippe

2010-02-15

It was demonstrated that CO(2) volume fluxes outgassing from a flute poured with a young champagne (elaborated in 2007) are much higher than those outgassing from the same flute poured with an older champagne (elaborated in the early 1990s). The difference in dissolved-CO(2) concentrations between the two types of champagne samples was found to be a crucial parameter responsible for differences in CO(2) volume fluxes outgassing from one champagne to another. Nevertheless, it was shown that, for a given identical dissolved-CO(2) concentration in both champagne types, the CO(2) volume flux outgassing from the flute poured with the old champagne is, in average, significantly lower than that outgassing from the flute poured with the young one. Therefore, CO(2) seems to "escape" more easily from the young champagne than from the older one. The diffusion coefficient of CO(2) in both champagne types was pointed as a key parameter to thoroughly determine in the future, in order to unravel our experimental observation. Copyright 2009 Elsevier B.V. All rights reserved.

Coastal upwelling fluxes of O2, N2O, and CO2 assessed from continuous atmospheric observations at Trinidad, California

Directory of Open Access Journals (Sweden)

T. J. Lueker

2004-01-01

Full Text Available Continuous atmospheric records of O2/N2, CO2 and N2O obtained at Trinidad, California document the effects of air-sea exchange during coastal upwelling and plankton bloom events. The atmospheric records provide continuous observations of air-sea fluxes related to synoptic scale upwelling events over several upwelling seasons. Combined with satellite, buoy and local meteorology data, calculated anomalies in O2/N2 and N2O were utilized in a simple atmospheric transport model to compute air-sea fluxes during coastal upwelling. CO2 fluxes were linked to the oceanic component of the O2 fluxes through local hydrographic data and estimated as a function of upwelling intensity (surface ocean temperature and wind speed. Regional air-sea fluxes of O2/N2, N2O, and CO2 during coastal upwelling were estimated with the aid of satellite wind and SST data. Upwelling CO2 fluxes were found to represent ~10% of export production along the northwest coast of North America. Synoptic scale upwelling events impact the net exchange of atmospheric CO2 along the coastal margin, and will vary in response to the frequency and duration of alongshore winds that are subject to climate change.

Interannual variability of Net Ecosystem CO2 Exchange and its component fluxes in a subalpine Mediterranean ecosystem (SE Spain)

Science.gov (United States)

Chamizo, Sonia; Serrano-Ortiz, Penélope; Sánchez-Cañete, Enrique P.; Domingo, Francisco; Arnau-Rosalén, Eva; Oyonarte, Cecilio; Pérez-Priego, Óscar; López-Ballesteros, Ana; Kowalski, Andrew S.

2015-04-01

Recent decades under climate change have seen increasing interest in quantifying the carbon (C) balance of different terrestrial ecosystems, and their behavior as sources or sinks of C. Both CO2 exchange between terrestrial ecosystems and the atmosphere and identification of its drivers are key to understanding land-surface feedbacks to climate change. The eddy covariance (EC) technique allows measurements of net ecosystem C exchange (NEE) from short to long time scales. In addition, flux partitioning models can extract the components of net CO2 fluxes, including both biological processes of photosynthesis or gross primary production (GPP) and respiration (Reco), and also abiotic drivers like subsoil CO2 ventilation (VE), which is of particular relevance in semiarid environments. The importance of abiotic processes together with the strong interannual variability of precipitation, which strongly affects CO2 fluxes, complicates the accurate characterization of the C balance in semiarid landscapes. In this study, we examine 10 years of interannual variability of NEE and its components at a subalpine karstic plateau, El Llano de los Juanes, in the Sierra de Gádor (Almería, SE Spain). Results show annual NEE ranging from 55 g C m-2 (net emission) to -54 g C m-2 (net uptake). Among C flux components, GPP was the greatest contributing 42-57% of summed component magnitudes, while contributions by Reco and VE ranged from 27 to 46% and from 3 to 18%, respectively. Annual precipitation during the studied period exhibited high interannual variability, ranging from 210 mm to 1374 mm. Annual precipitation explained 50% of the variance in Reco, 59% of that in GPP, and 56% for VE. While Reco and GPP were positively correlated with annual precipitation (correlation coefficient, R, of 0.71 and 0.77, respectively), VE showed negative correlation with this driver (R = -0.74). During the driest year (2004-2005), annual GPP and Reco reached their lowest values, while contribution of

Impact of hydrological variations on modeling of peatland CO2 fluxes: Results from the North American Carbon Program site synthesis

Science.gov (United States)

Sulman, Benjamin N.; Desai, Ankur R.; Schroeder, Nicole M.; Ricciuto, Dan; Barr, Alan; Richardson, Andrew D.; Flanagan, Lawrence B.; Lafleur, Peter M.; Tian, Hanqin; Chen, Guangsheng; Grant, Robert F.; Poulter, Benjamin; Verbeeck, Hans; Ciais, Philippe; Ringeval, Bruno; Baker, Ian T.; Schaefer, Kevin; Luo, Yiqi; Weng, Ensheng

2012-03-01

Northern peatlands are likely to be important in future carbon cycle-climate feedbacks due to their large carbon pools and vulnerability to hydrological change. Use of non-peatland-specific models could lead to bias in modeling studies of peatland-rich regions. Here, seven ecosystem models were used to simulate CO2fluxes at three wetland sites in Canada and the northern United States, including two nutrient-rich fens and one nutrient-poor,sphagnum-dominated bog, over periods between 1999 and 2007. Models consistently overestimated mean annual gross ecosystem production (GEP) and ecosystem respiration (ER) at all three sites. Monthly flux residuals (simulated - observed) were correlated with measured water table for GEP and ER at the two fen sites, but were not consistently correlated with water table at the bog site. Models that inhibited soil respiration under saturated conditions had less mean bias than models that did not. Modeled diurnal cycles agreed well with eddy covariance measurements at fen sites, but overestimated fluxes at the bog site. Eddy covariance GEP and ER at fens were higher during dry periods than during wet periods, while models predicted either the opposite relationship or no significant difference. At the bog site, eddy covariance GEP did not depend on water table, while simulated GEP was higher during wet periods. Carbon cycle modeling in peatland-rich regions could be improved by incorporating wetland-specific hydrology and by inhibiting GEP and ER under saturated conditions. Bogs and fens likely require distinct plant and soil parameterizations in ecosystem models due to differences in nutrients, peat properties, and plant communities.

How can mountaintop CO2 observations be used to constrain regional carbon fluxes?

Science.gov (United States)

Lin, John C.; Mallia, Derek V.; Wu, Dien; Stephens, Britton B.

2017-05-01

Despite the need for researchers to understand terrestrial biospheric carbon fluxes to account for carbon cycle feedbacks and predict future CO2 concentrations, knowledge of these fluxes at the regional scale remains poor. This is particularly true in mountainous areas, where complex meteorology and lack of observations lead to large uncertainties in carbon fluxes. Yet mountainous regions are often where significant forest cover and biomass are found - i.e., areas that have the potential to serve as carbon sinks. As CO2 observations are carried out in mountainous areas, it is imperative that they are properly interpreted to yield information about carbon fluxes. In this paper, we present CO2 observations at three sites in the mountains of the western US, along with atmospheric simulations that attempt to extract information about biospheric carbon fluxes from the CO2 observations, with emphasis on the observed and simulated diurnal cycles of CO2. We show that atmospheric models can systematically simulate the wrong diurnal cycle and significantly misinterpret the CO2 observations, due to erroneous atmospheric flows as a result of terrain that is misrepresented in the model. This problem depends on the selected vertical level in the model and is exacerbated as the spatial resolution is degraded, and our results indicate that a fine grid spacing of ˜ 4 km or less may be needed to simulate a realistic diurnal cycle of CO2 for sites on top of the steep mountains examined here in the American Rockies. In the absence of higher resolution models, we recommend coarse-scale models to focus on assimilating afternoon CO2 observations on mountaintop sites over the continent to avoid misrepresentations of nocturnal transport and influence.

First direct measurements of formaldehyde flux via eddy covariance: implications for missing in-canopy formaldehyde sources

Directory of Open Access Journals (Sweden)

J. P. DiGangi

2011-10-01

Full Text Available We report the first observations of formaldehyde (HCHO flux measured via eddy covariance, as well as HCHO concentrations and gradients, as observed by the Madison Fiber Laser-Induced Fluorescence Instrument during the BEACHON-ROCS 2010 campaign in a rural, Ponderosa Pine forest northwest of Colorado Springs, CO. A median noon upward flux of ~80 μg m⁻² h⁻¹ (~24 ppt_v m s⁻¹ was observed with a noon range of 37 to 131 μg m⁻² h⁻¹. Enclosure experiments were performed to determine the HCHO branch (3.5 μg m^-2 h⁻¹ and soil (7.3 μg m⁻² h⁻¹ direct emission rates in the canopy. A zero-dimensional canopy box model, used to determine the apportionment of HCHO source and sink contributions to the flux, underpredicted the observed HCHO flux by a factor of 6. Simulated increases in concentrations of species similar to monoterpenes resulted in poor agreement with measurements, while simulated increases in direct HCHO emissions and/or concentrations of species similar to 2-methyl-3-buten-2-ol best improved model/measurement agreement. Given the typical diurnal variability of these BVOC emissions and direct HCHO emissions, this suggests that the source of the missing flux is a process with both a strong temperature and radiation dependence.

Eddy covariance fluxes of the NO-O3-NO2 triad above the forest canopy at the ATTO Site in the Amazon Basin

Science.gov (United States)

Tsokankunku, Anywhere; Wolff, Stefan; Sörgel, Matthias; Berger, Martina; Zelger, Michael; Dlugi, Ralf

2017-04-01

Nitrogen monoxide (NO) and nitrogen dioxide (NO2) (denoted together as NOx) determine the abundance of the tropospheric oxidants OH, O3 and NO3 that regulate atmospheric self-cleaning. The three reactive trace gases NO, NO2 and O3 undergo a series of interconnected photochemical reactions and are often referred to as the NO-O3-NO2 triad. Ozone deposition is mainly controlled by stomatal uptake, thus contributes to oxidative stress for the plants. Similarly, nitrogen dioxide from above or below the canopy is deposited to leaves through stomatal uptake. NO emissions from soils contribute to above canopy O3 formation and accelerate OH recycling. Therefore, quantification of the exchange fluxes of these species between the atmosphere and the biosphere are important for atmospheric chemistry and ecosystem research as well. The eddy covariance method is state of the art for direct measurements of ecosystem fluxes of trace gases. Eddy covariance measurements of NOx in pristine environments are rare because of lack of availability of instruments with the required precision to resolve concentrations characteristic of these environments. The Amazon Tall Tower Observatory (ATTO) is located in a pristine rainforest environment in the Amazon basin about 150 km northeast of the city of Manaus. It is the ideal site for studying the biosphere-atmosphere exchange of the NO-O3-NO2 triad, being largely undisturbed by anthropogenic sources. During an intensive measurement campaign in November 2015 at the ATTO site, measurements of NO, NO2 and O3 were carried out at 42 m above ground level on the 80 m walk-up tower with a fast (5 Hz) and sensitive (radiation. Vertical concentration profile measurements of NO, NO2 and O3 were available at 8 levels on the INSTANT tower from a reactive trace gas profile system which has been operational at the site since 2012. From these measurements, we present eddy covariance fluxes of the NO-O3-NO2 triad. We relate the fluxes to the canopy

Water and CO2 fluxes over semiarid alpine steppe and humid alpine meadow ecosystems on the Tibetan Plateau

Science.gov (United States)

Wang, Lei; Liu, Huizhi; Shao, Yaping; Liu, Yang; Sun, Jihua

2018-01-01

Based on eddy covariance flux data from July 15, 2014, to December 31, 2015, the water and CO2 fluxes were compared over a semiarid alpine steppe (Bange, Tibetan Plateau) and a humid alpine meadow (Lijiang, Yunnan) on the Tibetan Plateau and its surrounding region. During the wet season, the evaporative fraction (EF) was strongly and linearly correlated with the soil water content (SWC) at Bange because of its sparse green grass cover. In contrast, the correlation between the EF at Lijiang and the SWC and the normalized difference vegetation index (NDVI) was very low because the atmosphere was close to saturation and the EF was relatively constant. In the dry season, the EF at both sites decreased with the SWC. The net ecosystem exchange (NEE) at Bange was largely depressed at noon, while this phenomenon did not occur at Lijiang. The saturated NEE at Bange was 24% of that at Lijiang. The temperature sensitivity coefficient of ecosystem respiration at Bange (1.7) was also much lower than that at Lijiang (3.4). The annual total NEE in 2015 was 21.8 and -230.0 g C m-2 yr-1 at Bange and Lijiang, respectively, and the NEE was tightly controlled by the NDVI at the two sites. The distinct differences in the water and CO2 fluxes at Bange and Lijiang are attributed to the large SWC difference and its effect on vegetation growth.

Integrating lysimeter drainage and eddy covariance flux measurements in a groundwater recharge model

DEFF Research Database (Denmark)

Vasquez, Vicente; Thomsen, Anton Gårde; Iversen, Bo Vangsø

2015-01-01

Field scale water balance is difficult to characterize because controls exerted by soils and vegetation are mostly inferred from local scale measurements with relatively small support volumes. Eddy covariance flux and lysimeters have been used to infer and evaluate field scale water balances...... because they have larger footprint areas than local soil moisture measurements.. This study quantifies heterogeneity of soil deep drainage (D) in four 12.5 m2 repacked lysimeters, compares evapotranspiration from eddy covariance (ETEC) and mass balance residuals of lysimeters (ETwbLys), and models D...

Importance of crop varieties and management practices: evaluation of a process-based model for simulating CO2 and H2O fluxes at five European maize (Zea mays L. sites

Directory of Open Access Journals (Sweden)

T. Gruenwald

2011-06-01

Full Text Available This paper is a modelling study of crop management impacts on carbon and water fluxes at a range of European sites. The model is a crop growth model (STICS coupled with a process-based land surface model (ORCHIDEE. The data are online eddy-covariance observations of CO2 and H2O fluxes at five European maize cultivation sites. The results show that the ORCHIDEE-STICS model explains up to 75 % of the observed daily net CO2 ecosystem exchange (NEE variance, and up to 79 % of the latent heat flux (LE variance at five sites. The model is better able to reproduce gross primary production (GPP variations than terrestrial ecosystem respiration (TER variations. We conclude that structural deficiencies in the model parameterizations of leaf area index (LAI and TER are the main sources of error in simulating CO2 and H2O fluxes. A number of sensitivity tests, with variable crop variety, nitrogen fertilization, irrigation, and planting date, indicate that any of these management factors is able to change NEE by more than 15 %, but that the response of NEE to management parameters is highly site-dependent. Changes in management parameters are found to impact not only the daily values of NEE and LE, but also the cumulative yearly values. In addition, LE is shown to be less sensitive to management parameters than NEE. Multi-site model evaluations, coupled with sensitivity analysis to management parameters, thus provide important information about model errors, which helps to improve the simulation of CO2 and H2O fluxes across European croplands.

Arctic Ocean CO2 uptake: an improved multiyear estimate of the air-sea CO2 flux incorporating chlorophyll a concentrations

Science.gov (United States)

Yasunaka, Sayaka; Siswanto, Eko; Olsen, Are; Hoppema, Mario; Watanabe, Eiji; Fransson, Agneta; Chierici, Melissa; Murata, Akihiko; Lauvset, Siv K.; Wanninkhof, Rik; Takahashi, Taro; Kosugi, Naohiro; Omar, Abdirahman M.; van Heuven, Steven; Mathis, Jeremy T.

2018-03-01

We estimated monthly air-sea CO2 fluxes in the Arctic Ocean and its adjacent seas north of 60° N from 1997 to 2014. This was done by mapping partial pressure of CO2 in the surface water (pCO2w) using a self-organizing map (SOM) technique incorporating chlorophyll a concentration (Chl a), sea surface temperature, sea surface salinity, sea ice concentration, atmospheric CO2 mixing ratio, and geographical position. We applied new algorithms for extracting Chl a from satellite remote sensing reflectance with close examination of uncertainty of the obtained Chl a values. The overall relationship between pCO2w and Chl a was negative, whereas the relationship varied among seasons and regions. The addition of Chl a as a parameter in the SOM process enabled us to improve the estimate of pCO2w, particularly via better representation of its decline in spring, which resulted from biologically mediated pCO2w reduction. As a result of the inclusion of Chl a, the uncertainty in the CO2 flux estimate was reduced, with a net annual Arctic Ocean CO2 uptake of 180 ± 130 Tg C yr-1. Seasonal to interannual variation in the CO2 influx was also calculated.

Observing Carbon Dioxide Fluxes on a Corn Field and a Native Savanna in the Colombian Orinoco River Region Using Eddy Covariance

Science.gov (United States)

Morales-Rincon, L. A.; Jimenez-Pizarro, R.; Rodríguez, N.

2016-12-01

The Orinoco River basin is expected to become Colombia's largest farming belt in the near future. Agriculture and land use change are the most important greenhouse gas (GHG) source in Colombia and one of the most important globally. At the same time, agriculture is one of the few economic sectors that is also able to act as a sink, e.g. through soil carbon storage. Emissions are largely determined by agricultural practices, thus practice identification and C flux monitoring are of paramount importance for mitigation alternative identification. During second semester of 2015, we measured CO2 fluxes over a commercial corn filed the Colombian Orinoco River Region using enclosed-path eddy covariance. The plot behaved as a CO2 sink during crop development. We found that inter-crop activities played a key role in defining whether the area acted as a net source or sink. Quantifying C fluxes at under local soil and meteorological conditions provides new high quality scientific information, which could be incorporated into a wider evaluation of agroindustry process, e.g. through the C footprint. We will also present ongoing carbon flux measurements in a native savanna and will discuss on the possibility of extrapolating our result to wider areas using process based models.

On which timescales do gas transfer velocities control North Atlantic CO2 flux variability?

OpenAIRE

Couldrey, Matthew; Oliver, Kevin; Yool, Andrew; Halloran, Paul; Achterberg, Eric

2016-01-01

The North Atlantic is an important basin for the global ocean's uptake of anthropogenic and natural carbon dioxide (CO2), but the mechanisms controlling this carbon flux are not fully understood. The air-sea flux of CO2, F, is the product of a gas transfer velocity, k, the air-sea CO2 concentration gradient, ΔpCO2, and the temperature and salinity-dependent solubility coefficient, α. k is difficult to constrain, representing the dominant uncertainty in F on short (instantaneous to interannual...

CO2 consumption and bicarbonate fluxes by chemical weathering in North America.

Science.gov (United States)

Jansen, Nils; Hartmann, Jens; Lauerwald, Ronny

2010-05-01

Cations released by chemical weathering are mainly counterbalanced by atmospheric/soil CO2 dissolved in water. Existing approaches to quantify CO2 consumption by chemical weathering are mostly based on the parameters runoff and lithology. Land cover is not implemented as predictor in existing regional or global scale models for atmospheric/soil CO2 consumption. Here, bicarbonate fluxes in North American rivers are quantified by an empirical forward model using the predictors runoff, lithology and land cover. The model was calibrated on chemical data from 338 river monitoring stations throughout North America. It was extrapolated to the entire North American continent by applying the model equation spatially explicitly to the geodata used for model calibration. Because silicate mineral weathering derived bicarbonate in rivers originates entirely from atmospheric/soil CO2, but carbonate mineral weathering additionally releases lithogenic bicarbonate, those source minerals are distinguished to quantify the CO2 consumption by chemical weathering. Extrapolation of the model results in a total bicarbonate flux of 51 Mt C a-1 in North America; 70% of which originate from atmospheric/soil CO2. On average, chemical weathering consumes 2.64 t atmospheric/soil C km-2 a-1 (~ 30%-40% above published world average values). For a given runoff and land cover, carbonate-rich sedimentary rocks export the most bicarbonate. However, half of this is assumed to be of lithogenic origin. Thus, the most atmospheric/soil CO2 per runoff is modeled to be consumed by basic plutonics. The least bicarbonate is exported and the least CO2 is consumed per runoff by weathering of metamorphic rocks. Of the distinguished different land cover classes of which urban areas export the most bicarbonate for a given lithology and runoff, followed by shrubs, grasslands and managed lands. For a given runoff and lithology, the least bicarbonate is exported from areas with forested land cover. The model shows 1

Application of Relaxed Eddy Accumulation (REA) method to estimate CO2 and CH4 surface fluxes in the city of Krakow, southern Poland.

Science.gov (United States)

Zimnoch, Miroslaw; Gorczyca, Zbigniew; Pieniazek, Katarzyna; Jasek, Alina; Chmura, Lukasz; Rozanski, Kazimierz

2013-04-01

There is a growing interest in the recent years in studies aimed at quantifying carbon cycling in urban centres. Worldwide migration of human population from rural to urban areas and corresponding growth of extensive urban agglomerations and megacities leads to intensification of anthropogenic emissions of carbon and strong disruption of natural carbon cycle on these areas. Therefore, a deeper understanding of the carbon "metabolism" of such regions is required. Apart of better quantification of surface carbon fluxes, also a thorough understanding of the functioning of biosphere under strong anthropogenic influence is needed. Nowadays, covariance methods are widely applied for studying gas exchange between the atmosphere and the Earth's surface. Relaxed Eddy Accumulation method (REA), combined with the CO2 and CH4 CRDS analyser allows simultaneous measurements of surface fluxes of carbon dioxide and methane within the chosen footprint of the detection system, thus making possible thorough characterisation of the overall exchange of those gases between the atmosphere and the urban surface across diverse spatial and temporal scales. Here we present preliminary results of the study aimed at quantifying surface fluxes of CO2 and CH4 in Krakow, southern Poland. The REA system for CO2 and CH4 flux measurements has been installed on top of a 20m high tower mounted on the roof of the faculty building, close to the city centre of Krakow. The sensors were installed ca 42 m above the local ground. Gill Windmaster-Pro sonic anemometer was coupled with self-made system, designed by the Poznan University of Life Sciences, Poland, for collecting air samples in two pairs of 10-liter Tedlar bags, and with Picarro G2101-i CRDS analyser. The air was collected in 30-min intervals. The CO2 and CH4 mixing ratios in these cumulative downdraft and updraft air samples were determined by the CRDS analyser after each sampling interval. Based on the measured mixing ratios difference and the

CO2 and CH4 fluxes from oil palm plantations in Sumatra, Indonesia: effects of palm age and environmental conditions

Science.gov (United States)

Meijide, A.; Hassler, E.; Corre, M. D.; June, T.; Sabajo, C.; Veldkamp, E.; Knohl, A.

2015-12-01

Global increasing demand of palm oil is leading to the expansion of oil palm plantations, particularly in SE Asia, which in Sumatran lowlands has resulted in a 21% forest area loss. Large photosynthesis rates are expected for oil palms, due to their high growth and yield production. However, there is very limited information on their effect on carbon dioxide (CO2) fluxes and their sink or source strength at ecosystem scale. For methane (CH4) fluxes, research has mainly focused in oil palm plantations located on peatlands, but no information is available at ecosystem level from plantations on mineral soils. With the aim of studying CO2 fluxes during the non-productive and productive phases of oil palm cultivation, an eddy covariance (EC) tower was installed in a 2 year old oil palm plantation, where it was measuring for 8 months, and was subsequently moved to a 12 year old plantation, both in the province of Jambi, Sumatra. The EC system consisted of a Licor 7500A and an ultrasonic Metek anemometer, operating at 10 Hz, installed on a 7m and 22m tower respectively. In the 12 year old plantation, the tower was also equipped with a Los Gatos FGGA-24EP, to assess CH4 fluxes. Chamber measurements were also carried out to obtain information on respiration and CH4 fluxes from the soil. Radiation was the major driver controlling net carbon uptake, while soil moisture did not play a significant role. Average net ecosystem exchange in the hours of the day with higher radiation for the whole measurement period was 10 μmol m-2 s-1 for the 2 year old plantation and -22 μmol m-2 s-1 in the 12 year old. The analysis of the cumulative fluxes show that the non-productive plantation was a carbon source of around 636 g CO2 m-2 during the 8 months of measurements, while in the productive period, it acted as a strong carbon sink (-794 g CO2 m-2 yr-1). Methane uptake was observed in the soil in both plantations and also for the whole ecosystem in the 12 year old one, but its

Monitoring gas and heat emissions at Norris Geyser Basin, Yellowstone National Park, USA based on a combined eddy covariance and Multi-GAS approach

Science.gov (United States)

Lewicki, J. L.; Kelly, P. J.; Bergfeld, D.; Vaughan, R. G.; Lowenstern, J. B.

2017-11-01

We quantified gas and heat emissions in an acid-sulfate, vapor-dominated area (0.04-km2) of Norris Geyser Basin, located just north of the 0.63 Ma Yellowstone Caldera and near an area of anomalous uplift. From 14 May to 3 October 2016, an eddy covariance system measured half-hourly CO2, H2O and sensible (H) and latent (LE) heat fluxes and a Multi-GAS instrument measured (1 Hz frequency) atmospheric H2O, CO2 and H2S volumetric mixing ratios. We also measured soil CO2 fluxes using the accumulation chamber method and temperature profiles on a grid and collected fumarole gas samples for geochemical analysis. Eddy covariance CO2 fluxes ranged from - 56 to 885 g m- 2 d- 1. Using wavelet analysis, average daily eddy covariance CO2 fluxes were locally correlated with average daily environmental parameters on several-day to monthly time scales. Estimates of CO2 emission rate from the study area ranged from 8.6 t d- 1 based on eddy covariance measurements to 9.8 t d- 1 based on accumulation chamber measurements. Eddy covariance water vapor fluxes ranged from 1178 to 24,600 g m- 2 d- 1. Nighttime H and LE were considered representative of hydrothermal heat fluxes and ranged from 4 to 183 and 38 to 504 W m- 2, respectively. The total hydrothermal heat emission rate (H + LE + radiant) estimated for the study area was 11.6 MW and LE contributed 69% of the output. The mean ± standard deviation of H2O, CO2 and H2S mixing ratios measured by the Multi-GAS system were 9.3 ± 3.1 parts per thousand, 467 ± 61 ppmv, and 0.5 ± 0.6 ppmv, respectively, and variations in the gas compositions were strongly correlated with diurnal variations in environmental parameters (wind speed and direction, atmospheric temperature). After removing ambient H2O and CO2, the observed variations in the Multi-GAS data could be explained by the mixing of relatively H2O-CO2-H2S-rich fumarole gases with CO2-rich and H2O-H2S-poor soil gases. The fumarole H2O/CO2 and CO2/H2S end member ratios (101.7 and 27

Monitoring gas and heat emissions at Norris Geyser Basin, Yellowstone National Park, USA based on a combined eddy covariance and Multi-GAS approach

Science.gov (United States)

Lewicki, Jennifer L.; Kelly, Peter; Bergfeld, Deborah; Vaughan, R. Greg; Lowenstern, Jacob B.

2017-01-01

We quantified gas and heat emissions in an acid-sulfate, vapor-dominated area (0.04-km2) of Norris Geyser Basin, located just north of the 0.63 Ma Yellowstone Caldera and near an area of anomalous uplift. From 14 May to 3 October 2016, an eddy covariance system measured half-hourly CO2, H2O and sensible (H) and latent (LE) heat fluxes and a Multi-GAS instrument measured (1 Hz frequency) atmospheric H2O, CO2 and H2S volumetric mixing ratios. We also measured soil CO2 fluxes using the accumulation chamber method and temperature profiles on a grid and collected fumarole gas samples for geochemical analysis. Eddy covariance CO2 fluxes ranged from − 56 to 885 g m− 2 d− 1. Using wavelet analysis, average daily eddy covariance CO2 fluxes were locally correlated with average daily environmental parameters on several-day to monthly time scales. Estimates of CO2emission rate from the study area ranged from 8.6 t d− 1 based on eddy covariance measurements to 9.8 t d− 1 based on accumulation chamber measurements. Eddy covariance water vapor fluxes ranged from 1178 to 24,600 g m− 2 d− 1. Nighttime H and LEwere considered representative of hydrothermal heat fluxes and ranged from 4 to 183 and 38 to 504 W m− 2, respectively. The total hydrothermal heat emission rate (H + LE + radiant) estimated for the study area was 11.6 MW and LE contributed 69% of the output. The mean ± standard deviation of H2O, CO2 and H2S mixing ratios measured by the Multi-GAS system were 9.3 ± 3.1 parts per thousand, 467 ± 61 ppmv, and 0.5 ± 0.6 ppmv, respectively, and variations in the gas compositions were strongly correlated with diurnal variations in environmental parameters (wind speed and direction, atmospheric temperature). After removing ambient H2O and CO2, the observed variations in the Multi-GAS data could be explained by the mixing of relatively H2O-CO2-H2S-rich fumarole gases with CO2-rich and H2O-H2S-poor soil gases. The

Eddy Covariance Measurements Over a Maize Field: The Contribution of Minor Flux Terms to the Energy Balance Gap

Science.gov (United States)

Smidt, J.; Ingwersen, J.; Streck, T.

2015-12-01

The lack of energy balance closure is a long-standing problem in eddy covariance (EC) measurements. The energy balance equation is defined as Rn - G = H + λE, where Rn is net radiation, G is the ground heat flux, H is the sensible heat flux and λE is the latent heat flux. In most cases of energy imbalance, either Rn is overestimated or the ground heat and turbulent fluxes are underestimated. Multiple studies have shown that calculations, incorrect instrument installation/calibration and measurement errors alone do not entirely account for this imbalance. Rather, research is now focused on previously neglected sources of heat storage in the soil, biomass and air beneath the EC station. This project examined the potential of five "minor flux terms" - soil heat storage, biomass heat storage, energy consumption by photosynthesis, air heat storage and atmospheric moisture change, to further close the energy balance gap. Eddy covariance measurements were conducted at a maize (Zea mays) field in southwest Germany during summer 2014. Soil heat storage was measured for six weeks at 11 sites around the field footprint. Biomass and air heat storage were measured for six subsequent weeks at seven sites around the field footprint. Energy consumption by photosynthesis was calculated using the CO2 flux data. Evapotranspiration was calculated using the water balance method and then compared to the flux data processed with three post-closure methods: the sensible heat flux, the latent heat flux and the Bowen ratio post-closure methods. An energy balance closure of 66% was achieved by the EC station measurements over the entire investigation period. During the soil heat flux campaign, EC station closure was 74.1%, and the field footprint soil heat storage contributed 3.3% additional closure. During the second minor flux term measurement period, closure with the EC station data was 91%. Biomass heat storage resulted in 1.1% additional closure, the photosynthesis flux closed the gap

Rain-induced changes in soil CO2 flux and microbial community composition in a tropical forest of China.

Science.gov (United States)

Deng, Qi; Hui, Dafeng; Chu, Guowei; Han, Xi; Zhang, Quanfa

2017-07-17

Rain-induced soil CO 2 pulse, a rapid excitation in soil CO 2 flux after rain, is ubiquitously observed in terrestrial ecosystems, yet the underlying mechanisms in tropical forests are still not clear. We conducted a rain simulation experiment to quantify rain-induced changes in soil CO 2 flux and microbial community composition in a tropical forest. Soil CO 2 flux rapidly increased by ~83% after rains, accompanied by increases in both bacterial (~51%) and fungal (~58%) Phospholipid Fatty Acids (PLFA) biomass. However, soil CO 2 flux and microbial community in the plots without litters showed limited response to rains. Direct releases of CO 2 from litter layer only accounted for ~19% increases in soil CO 2 flux, suggesting that the leaching of dissolved organic carbon (DOC) from litter layer to the topsoil is the major cause of rain-induced soil CO 2 pulse. In addition, rain-induced changes in soil CO 2 flux and microbial PLFA biomass decreased with increasing rain sizes, but they were positively correlated with litter-leached DOC concentration rather than total DOC flux. Our findings reveal an important role of litter-leached DOC input in regulating rain-induced soil CO 2 pulses and microbial community composition, and may have significant implications for CO 2 losses from tropical forest soils under future rainfall changes.

Statistical partitioning of a three-year time series of direct urban net CO2 flux measurements into biogenic and anthropogenic components

Science.gov (United States)

Menzer, Olaf; McFadden, Joseph P.

2017-12-01

Eddy covariance flux measurements are increasingly used to quantify the net carbon dioxide exchange (FC) in urban areas. FC represents the sum of anthropogenic emissions, biogenic carbon release from plant and soil respiration, and carbon uptake by plant photosynthesis. When FC is measured in natural ecosystems, partitioning into respiration and photosynthesis is a well-established procedure. In contrast, few studies have partitioned FC at urban flux tower sites due to the difficulty of accounting for the temporal and spatial variability of the multiple sources and sinks. Here, we partitioned a three-year time series of flux measurements from a suburban neighborhood of Minneapolis-Saint Paul, Minnesota, USA. We segregated FC into one subset that captured fluxes from a residential neighborhood and into another subset that covered a golf course. For both land use types we modeled anthropogenic flux components based on winter data and extrapolated them to the growing season, to estimate gross primary production (GPP) and ecosystem respiration (Reco) at half-hourly, daily, monthly and annual scales. During the growing season, GPP had the largest magnitude (up to - 9.83 g C m-2 d-1) of any component CO2 flux, biogenic or anthropogenic, and both GPP and Reco were more dynamic seasonally than anthropogenic fluxes. Owing to the balancing of Reco against GPP, and the limitations of the growing season in a cold temperate climate zone, the net biogenic flux was only 1.5%-4.5% of the anthropogenic flux in the dominant residential land use type, and between 25%-31% of the anthropogenic flux in highly managed greenspace. Still, the vegetation sink at our site was stronger than net anthropogenic emissions on 16-20 days over the residential area and on 66-91 days over the recreational area. The reported carbon flux sums and dynamics are a critical step toward developing models of urban CO2 fluxes within and across cities that differ in vegetation cover.

Potentials and challenges associated with automated closed dynamic chamber measurements of soil CO2 fluxes

Science.gov (United States)

Görres, Carolyn-Monika; Kammann, Claudia; Ceulemans, Reinhart

2015-04-01

Soil respiration fluxes are influenced by natural factors such as climate and soil type, but also by anthropogenic activities in managed ecosystems. As a result, soil CO2 fluxes show a large intra- and interannual as well as intra- and intersite variability. Most of the available soil CO2 flux data giving insights into this variability have been measured with manually closed static chambers, but technological advances in the past 15 years have also led to an increased use of automated closed chamber systems. The great advantage of automated chambers in comparison to manually operated chambers is the higher temporal resolution of the flux data. This is especially important if we want to better understand the effects of short-term events, e.g. fertilization or heavy rainfall, on soil CO2 flux variability. However, the chamber method is an invasive measurement method which can potentially alter soil CO2 fluxes and lead to biased measurement results. In the peer-reviewed literature, many papers compare the field performance and results of different closed static chamber designs, or compare manual chambers with automated chamber systems, to identify potential biases in CO2 flux measurements, and thus help to reduce uncertainties in the flux data. However, inter-comparisons of different automated closed dynamic chamber systems are still lacking. Here we are going to present a field comparison of the most-cited automated chamber system, the LI-8100A Automated Soil Flux System, with the also commercially available Greenhouse Gas Monitoring System AGPS. Both measurement systems were installed side by side at a recently harvested poplar bioenergy plantation (POPFULL, http://uahost.uantwerpen.be/popfull/) from April 2014 until August 2014. The plantation provided optimal comparison conditions with a bare field situation after the harvest and a regrowing canopy resulting in a broad variety of microclimates. Furthermore, the plantation was planted in a double-row system with

Aircraft vertical profiling of variation of CO2 over a Canadian Boreal Forest Site: a role of advection in the changes in the atmospheric boundary layer CO2 content

International Nuclear Information System (INIS)

Shashkov, Alexander; Higuchi, Kaz; Chan, Douglas

2007-01-01

During the period of July 8-13, 2002, we collected vertical profiles by aircraft of meteorological variables and atmospheric CO 2 over the OBS (old black spruce) site located in Boreal Ecosystem Research and Monitoring Sites in Northern Saskatchewan, Canada. We have used the data from the morning and afternoon flights to calculate the regional daily afternoon CO 2 flux for the days July 8-11. These daily fluxes were then compared to those obtained by the boundary layer budget method and by the eddy covariance measurements on the tower at the OBS site. We identified the importance of changes in the CO 2 concentration by advection to the flux estimates. In addition, we provide arguments to suggest that subseasonal temporal averaging might not, at least in some cases, eliminate advective bias contribution to the flux estimates. Because the advective influence is large and highly directional, even on seasonal and interannual timescales, it is advisable that flux estimates based on CO 2 concentration change at a site contain dynamic description of an air parcel transport history

Soil CO2 flux in response to wheel traffic in a no-till system

Science.gov (United States)

Measurements of soil CO2 flux in the absence of living plants can be used to evaluate the effectiveness of soil management practices for C sequestration, but field CO2 flux is spatially variable and may be affected by soil compaction and percentage of total pore space filled with water (%WFPS). The ...

Responses of soil CO2 fluxes to short-term experimental warming in alpine steppe ecosystem, Northern Tibet.

Science.gov (United States)

Lu, Xuyang; Fan, Jihui; Yan, Yan; Wang, Xiaodan

2013-01-01

Soil carbon dioxide (CO2) emission is one of the largest fluxes in the global carbon cycle. Therefore small changes in the size of this flux can have a large effect on atmospheric CO2 concentrations and potentially constitute a powerful positive feedback to the climate system. Soil CO2 fluxes in the alpine steppe ecosystem of Northern Tibet and their responses to short-term experimental warming were investigated during the growing season in 2011. The results showed that the total soil CO2 emission fluxes during the entire growing season were 55.82 and 104.31 g C m(-2) for the control and warming plots, respectively. Thus, the soil CO2 emission fluxes increased 86.86% with the air temperature increasing 3.74°C. Moreover, the temperature sensitivity coefficient (Q 10) of the control and warming plots were 2.10 and 1.41, respectively. The soil temperature and soil moisture could partially explain the temporal variations of soil CO2 fluxes. The relationship between the temporal variation of soil CO2 fluxes and the soil temperature can be described by exponential equation. These results suggest that warming significantly promoted soil CO2 emission in the alpine steppe ecosystem of Northern Tibet and indicate that this alpine ecosystem is very vulnerable to climate change. In addition, soil temperature and soil moisture are the key factors that controls soil organic matter decomposition and soil CO2 emission, but temperature sensitivity significantly decreases due to the rise in temperature.

On the use of satellite-derived CH4 : CO2 columns in a joint inversion of CH4 and CO2 fluxes

NARCIS (Netherlands)

Pandey, S.

2015-01-01

We present a method for assimilating total column CH4 : CO2 ratio measurements from satellites for inverse modeling of CH4 and CO2 fluxes using the variational approach. Unlike conventional approaches, in which retrieved CH4 : CO2 are multiplied by model-derived total column CO2 and only the

Land use and rainfall effect on soil CO2 fluxes in a Mediterranean agroforestry system

Science.gov (United States)

Quijano, Laura; Álvaro-Fuentes, Jorge; Lizaga, Iván; Navas, Ana

2017-04-01

Soils are the largest C reservoir of terrestrial ecosystems and play an important role in regulating the concentration of CO2 in the atmosphere. The exchange of CO2 between the atmosphere and soil controls the balance of C in soils. The CO2 fluxes may be influenced by climate conditions and land use and cover change especially in the upper soil organic layer. Understanding C dynamics is important for maintaining C stocks to sustain and improve soil quality and to enhance sink C capacity of soils. This study focuses on the response of the CO2 emitted to rainfall events from different land uses (i.e. forest, abandoned cultivated soils and winter cereal cultivated soils) in a representative Mediterranean agroforestry ecosystem in the central part of the Ebro basin, NE Spain (30T 4698723N 646424E). A total of 30 measurement points with the same soil type (classified as Calcisols) were selected. Soil CO2 flux was measured in situ using a portable EGM-4 CO2 analyzer PPSystems connected to a dynamic chamber system (model CFX-1, PPSystems) weekly during autumn 2016. Eleven different rainfall events were measured at least 24 hours before (n=7) and after the rainfall event (n=4). Soil water content and temperature were measured at each sampling point within the first 5 cm. Soil samples were taken at the beginning of the experiment to determine soil organic carbon (SOC) content using a LECO RC-612. The mean SOC for forest, abandoned and cultivated soils were 2.5, 2.7 and 0.6 %, respectively. The results indicated differences in soil CO2 fluxes between land uses. The field measurements of CO2 flux show that before cereal sowing the highest values were recorded in the abandoned soils varying from 56.1 to 171.9 mg CO2-C m-2 h-1 whereas after cereal sowing the highest values were recorded in cultivated soils ranged between 37.8 and 116.2 mg CO2-C m-2 h-1 indicating the agricultural impact on CO2 fluxes. In cultivated soils, lower mean CO2 fluxes were measured after direct seeding

Directional selection effects on patterns of phenotypic (co)variation in wild populations.

Science.gov (United States)

Assis, A P A; Patton, J L; Hubbe, A; Marroig, G

2016-11-30

Phenotypic (co)variation is a prerequisite for evolutionary change, and understanding how (co)variation evolves is of crucial importance to the biological sciences. Theoretical models predict that under directional selection, phenotypic (co)variation should evolve in step with the underlying adaptive landscape, increasing the degree of correlation among co-selected traits as well as the amount of genetic variance in the direction of selection. Whether either of these outcomes occurs in natural populations is an open question and thus an important gap in evolutionary theory. Here, we documented changes in the phenotypic (co)variation structure in two separate natural populations in each of two chipmunk species (Tamias alpinus and T. speciosus) undergoing directional selection. In populations where selection was strongest (those of T. alpinus), we observed changes, at least for one population, in phenotypic (co)variation that matched theoretical expectations, namely an increase of both phenotypic integration and (co)variance in the direction of selection and a re-alignment of the major axis of variation with the selection gradient. © 2016 The Author(s).

Nitrous oxide flux under changing temperature and CO2

Science.gov (United States)

We are investigating nitrous oxide flux seasonal trends and response to temperature and CO2 increases in a boreal peatland. Peatlands located in boreal regions make up a third of global wetland area and are expected to have the highest temperature increases in response to climat...

Eddy Correlation Flux Measurement System (ECOR) Handbook

Energy Technology Data Exchange (ETDEWEB)

Cook, DR

2011-01-31

The eddy correlation (ECOR) flux measurement system provides in situ, half-hour measurements of the surface turbulent fluxes of momentum, sensible heat, latent heat, and carbon dioxide (CO2) (and methane at one Southern Great Plains extended facility (SGP EF) and the North Slope of Alaska Central Facility (NSA CF). The fluxes are obtained with the eddy covariance technique, which involves correlation of the vertical wind component with the horizontal wind component, the air temperature, the water vapor density, and the CO2 concentration.

High-frequency pressure variations in the vicinity of a surface CO2 flux chamber

Science.gov (United States)

Eugene S. Takle; James R. Brandle; R. A. Schmidt; Rick Garcia; Irina V. Litvina; William J. Massman; Xinhua Zhou; Geoffrey Doyle; Charles W. Rice

2003-01-01

We report measurements of 2Hz pressure fluctuations at and below the soil surface in the vicinity of a surface-based CO2 flux chamber. These measurements were part of a field experiment to examine the possible role of pressure pumping due to atmospheric pressure fluctuations on measurements of surface fluxes of CO2. Under the moderate wind speeds, warm temperatures,...

Seasonal variation of CO{sub 2} flux between air and temperate forest

Energy Technology Data Exchange (ETDEWEB)

Yamamoto, Susumo; Murayama, Shohei; Kondo, Hiroaki [National Inst. for Resources and Environment, Ibaraki (Japan)

1995-12-31

Carbon dioxide, which is a very important greenhouse gas, contributes approximately 55 % to the problem of global warming. The knowledge to the sources and sinks of carbon on a global basis is very poor. IPCC (1994) suggested that unknown 1.5-2.0 GtC/year may be sunk in terrestrial ecosystem, in particular, in the Northern Hemisphere. As can be seen from a recent estimation of the carbon fluxes in the terrestrial biosphere, there is a high degree of uncertainty in the magnitude. The clear evidence for it has not been shown yet by IPCC (1994). However, based on the gradient of CO{sub 2}, as a function of latitude, main CO{sub 2} sink can be thought to be in the terrestrial biosphere, in the middle to high latitude of the Northern Hemisphere. As can be seen from a recent estimation of the carbon fluxes in the terrestrial biosphere, there is a high degree of uncertainty in the magnitude. From this view, more investigation of the role of the temperate forest on the CO{sub 2} balance is inevitable. In this presentation, the seasonal variation of CO{sub 2} flux between air and biosphere in temperate deciduous forest in Japan is intended to be elucidated. (author)

Seasonal variation of CO{sub 2} flux between air and temperate forest

Energy Technology Data Exchange (ETDEWEB)

Yamamoto, Susumo; Murayama, Shohei; Kondo, Hiroaki [National Inst. for Resources and Environment, Ibaraki (Japan)

1996-12-31

Carbon dioxide, which is a very important greenhouse gas, contributes approximately 55 % to the problem of global warming. The knowledge to the sources and sinks of carbon on a global basis is very poor. IPCC (1994) suggested that unknown 1.5-2.0 GtC/year may be sunk in terrestrial ecosystem, in particular, in the Northern Hemisphere. As can be seen from a recent estimation of the carbon fluxes in the terrestrial biosphere, there is a high degree of uncertainty in the magnitude. The clear evidence for it has not been shown yet by IPCC (1994). However, based on the gradient of CO{sub 2}, as a function of latitude, main CO{sub 2} sink can be thought to be in the terrestrial biosphere, in the middle to high latitude of the Northern Hemisphere. As can be seen from a recent estimation of the carbon fluxes in the terrestrial biosphere, there is a high degree of uncertainty in the magnitude. From this view, more investigation of the role of the temperate forest on the CO{sub 2} balance is inevitable. In this presentation, the seasonal variation of CO{sub 2} flux between air and biosphere in temperate deciduous forest in Japan is intended to be elucidated. (author)

Eddy Covariance Measurements of Methane Flux at Remote Sites with New Low-Power Lightweight Fast Gas Analyzer

Science.gov (United States)

Xu, Liukang; Burba, George; Schedlbauer, Jessica; Zona, Donatella; McDermitt, Dayle K.; Anderson, Tyler; Oberbauer, Steven; Oechel, Walter; Komissarov, Anatoly; Riensche, Brad

2010-05-01

Majority of natural methane production happens at remote unpopulated areas in ecosystems with little or no infrastructure or easily available grid power, such as arctic and boreal wetlands, tropical mangroves, etc. Present approaches for direct measurements of CH4 fluxes rely on fast closed-path analyzers, which have to work under significantly reduced pressures, and require powerful pumps and grid power. Power and labor demands may be reasons why CH4 flux is often measured at locations with good infrastructure and grid power, and not with high CH4 production. An instrument was developed to allow Eddy Covariance measurements of CH4 flux with power consumption 30-150 times below presently available technologies. This instrument, LI-7700, uses proposed extremely low-power technology would allows placing methane Eddy Covariance stations in the middle of the source (wetland, rice paddy, forest, etc.) in the absence of the grid power. This could significantly expand the Eddy Covariance CH4 flux measurements coverage, and possibly, significantly improve the budget estimates of world CH4 emissions and budget. Various prototypes of the LI-7700 were field-tested for three seasons at the remote site in middle of Everglades National Park (Florida, USA) using solar panels, at three stationary and several mobile sites during three seasons at remote Arctic wetlands near Barrow (Alaska, USA), in the tropical mangroves near La Paz (Mexico) using portable generator, and in bare agricultural field near Mead (Nebraska, USA) during 2005 through 2010. Latest data on CH4 concentration, co-spectra and fluxes, and latest details of instrumental design are examined in this presentation. Overall, hourly methane fluxes ranged from near-zero at night to about 4 mg m-2 h-1 in midday in arctic tundra. Observed fluxes were within the ranges reported in the literature for a number of wetlands in North America, including the Everglades wetlands. Diurnal patterns were similar to those measured by

Temporal and spatial variations of oceanic pCO2 and air-sea CO2 flux in th Greenland Sea and the Barents Sea

International Nuclear Information System (INIS)

Nakaoka, Shin-Ichiro; Aoki, Shuji; Nakazawa, Takakiyo; Yoshikawa-Inoue, Hisayuki

2006-01-01

In order to elucidate the seasonal and inter annual variations of oceanic CO 2 uptake in the Greenland Sea and the Barents Sea, the partial pressure of CO 2 in the surface ocean (pCO 2 sea ) was measured in all seasons between 1992 and 2001. We derived monthly varying relationships between pCO 2 sea and sea surface temperature (SST) and combined them with the SST data from the NCEP/NCAR reanalysis to determine pCO 2 sea and air-sea CO 2 flux in these seas. The pCO 2 sea values were normalized to the year 1995 by assuming that pCO 2 sea increased at the same growth rate (1.5 μatm/yr) of the pCO 2 in the air (pCO 2 air ) between 1992 and 2001. In 1995, the annual net air-sea CO 2 fluxes were evaluated to be 52 ± 20 gC/m 2 /yr in the Greenland Sea and 46 ± 18 gC/m 2 /yr in the Barents Sea. The CO 2 flux into the ocean reached its maximum in winter and minimum in summer. The wind speed and (delta)pCO 2 (=pCO 2 air -pCO 2 sea ) exerted a greater influence on the seasonal variation than the sea ice coverage. The annual CO 2 uptake examined in this study (70-80 deg N, 20 deg W-40 deg E) was estimated to be 0.050 ± 0.020 GtC/yr in 1995. The inter annual variation in the annual CO 2 uptake was found to be positively correlated with the North Atlantic Oscillation Index (NAOI) via wind strength but negatively correlated with (delta)pCO 2 and the sea ice coverage. The present results indicate that the variability in wind speed and sea ice coverage play a major role, while that in (delta)pCO 2 plays a minor role, in determining the interannual variation of CO 2 uptake in this area

Productivity and CO2 exchange of Great Plains ecoregions. I. Shortgrass steppe: Flux tower estimates

Science.gov (United States)

Gilmanov, Tagir G.; Morgan, Jack A.; Hanan, Niall P.; Wylie, Bruce K.; Rajan, Nithya; Smith, David P.; Howard, Daniel M.

2017-01-01

The shortgrass steppe (SGS) occupies the southwestern part of the Great Plains. Half of the land is cultivated, but significant areas remain under natural vegetation. Despite previous studies of the SGS carbon cycle, not all aspects have been completely addressed, including gross productivity, ecosystem respiration, and ecophysiological parameters. Our analysis of 1998 − 2007 flux tower measurements at five Bowen ratio–energy balance (BREB) and three eddy covariance (EC) sites characterized seasonal and interannual variability of gross photosynthesis and ecosystem respiration. Identification of the nonrectangular hyperbolic equation for the diurnal CO2 exchange, with vapor pressure deficit (VPD) limitation and exponential temperature response, quantified quantum yield α, photosynthetic capacity Amax, and respiration rate rd with variation ranges (19 \\production from − 900 to + 700 g CO2 m− 2 yr− 1, indicating that SGS may switch from a sink to a source depending on weather. Comparison of the 2004 − 2006 measurements at two BREB and two parallel EC flux towers located at comparable SGS sites showed moderately higher photosynthesis, lower respiration, and higher net production at the BREB than EC sites. However, the difference was not related only to methodologies, as the normalized difference vegetation index at the BREB sites was higher than at the EC sites. Overall magnitudes and seasonal patterns at the BREB and the EC sites during the 3-yr period were similar, with trajectories within the ± 1.5 standard deviation around the mean of the four sites and mostly reflecting the effects of meteorology.

CO2, CH4 and N2O fluxes from soil of a burned grassland in Central Africa

Directory of Open Access Journals (Sweden)

R. Valentini

2010-11-01

Full Text Available The impact of fire on soil fluxes of CO2, CH4 and N2O was investigated in a tropical grassland in Congo Brazzaville during two field campaigns in 2007–2008. The first campaign was conducted in the middle of the dry season and the second at the end of the growing season, respectively one and eight months after burning. Gas fluxes and several soil parameters were measured in each campaign from burned plots and from a close-by control area preserved from fire. Rain events were simulated at each campaign to evaluate the magnitude and duration of the generated gas flux pulses. In laboratory experiments, soil samples from field plots were analysed for microbial biomass, net N mineralization, net nitrification, N2O, NO and CO2 emissions under different water and temperature soil regimes. One month after burning, field CO2 emissions were significantly lower in burned plots than in the control plots, the average daily CH4 flux shifted from net emission in the unburned area to net consumption in burned plots, no significant effect of fire was observed on soil N2O fluxes. Eight months after burning, the average daily fluxes of CO2, CH4 and N2O measured in control and burned plots were not significantly different. In laboratory, N2O fluxes from soil of burned plots were significantly higher than fluxes from soil of unburned plots only above 70% of maximum soil water holding capacity; this was never attained in the field even after rain simulation. Higher NO emissions were measured in the lab in soil from burned plots at both 10% and 50% of maximum soil water holding capacity. Increasing the incubation temperature from 25 °C to 37 °C negatively affected microbial growth, mineralization and nitrification activities but enhanced N2O and CO2 production. Results indicate that fire did not increase post-burning soil GHG emissions in this tropical grasslands characterized by acidic, well drained and nutrient-poor soil.

Variability and budget of CO2 in Europe: analysis of the CAATER airborne campaigns - Part 2: Comparison of CO2 vertical variability and fluxes between observations and a modeling framework

International Nuclear Information System (INIS)

Xueref-Remy, I.; Bousquet, P.; Rivier, L.; Ciais, P.; Carouge, C.

2011-01-01

Our ability to predict future climate change relies on our understanding of current and future CO 2 fluxes, particularly on a regional scale (100-1000 km). CO 2 regional sources and sinks are still poorly understood. Inverse transport modeling, a method often used to quantify these fluxes, relies on atmospheric CO 2 measurements. One of the main challenges for the transport models used in the inversions is to properly reproduce CO 2 vertical gradients between the boundary layer and the free troposphere, as these gradients impact on the partitioning of the calculated fluxes between the different model regions. Vertical CO 2 profiles are very well suited to assess the performances of the models. In this paper, we conduct a comparison between observed and modeled CO 2 profiles recorded during two CAATER campaigns that occurred in May 2001 and October 2002 over Western Europe, as described in a companion paper. We test different combinations between a global transport model (LMDZt), a mesoscale transport model (CHIMERE), and different sets of biospheric fluxes, all chosen with a diurnal cycle (CASA, SiB2 and ORCHIDEE). The vertical profile comparison shows that: 1) in most cases the influence of the biospheric flux is small but sometimes not negligible, ORCHIDEE giving the best results in the present study; 2) LMDZt is most of the time too diffuse, as it simulates a too high boundary layer height; 3) CHIMERE better reproduces the observed gradients between the boundary layer and the free troposphere, but is sometimes too variable and gives rise to incoherent structures. We conclude there is a need for more vertical profiles to conduct further studies to improve the parameterization of vertical transport in the models used for CO 2 flux inversions. Furthermore, we use a modeling method to quantify CO 2 fluxes at the regional scale from a chosen observing point, coupling influence functions from the transport model LMDZt (that works quite well at the synoptic scale) with

On which timescales do gas transfer velocities control North Atlantic CO2 flux variability?

Science.gov (United States)

Couldrey, Matthew P.; Oliver, Kevin I. C.; Yool, Andrew; Halloran, Paul R.; Achterberg, Eric P.

2016-05-01

The North Atlantic is an important basin for the global ocean's uptake of anthropogenic and natural carbon dioxide (CO2), but the mechanisms controlling this carbon flux are not fully understood. The air-sea flux of CO2, F, is the product of a gas transfer velocity, k, the air-sea CO2 concentration gradient, ΔpCO2, and the temperature- and salinity-dependent solubility coefficient, α. k is difficult to constrain, representing the dominant uncertainty in F on short (instantaneous to interannual) timescales. Previous work shows that in the North Atlantic, ΔpCO2 and k both contribute significantly to interannual F variability but that k is unimportant for multidecadal variability. On some timescale between interannual and multidecadal, gas transfer velocity variability and its associated uncertainty become negligible. Here we quantify this critical timescale for the first time. Using an ocean model, we determine the importance of k, ΔpCO2, and α on a range of timescales. On interannual and shorter timescales, both ΔpCO2 and k are important controls on F. In contrast, pentadal to multidecadal North Atlantic flux variability is driven almost entirely by ΔpCO2; k contributes less than 25%. Finally, we explore how accurately one can estimate North Atlantic F without a knowledge of nonseasonal k variability, finding it possible for interannual and longer timescales. These findings suggest that continued efforts to better constrain gas transfer velocities are necessary to quantify interannual variability in the North Atlantic carbon sink. However, uncertainty in k variability is unlikely to limit the accuracy of estimates of longer-term flux variability.

Soil methane and CO2 fluxes in rainforest and rubber plantations

Science.gov (United States)

Lang, Rong; Blagodatsky, Sergey; Goldberg, Stefanie; Xu, Jianchu

2017-04-01

Expansion of rubber plantations in South-East Asia has been a land use transformation trend leading to losses of natural forest cover in the region. Besides impact on ecosystem carbon stocks, this conversion influences the dynamics of greenhouse gas fluxes from soil driven by microbial activity, which has been insufficiently studied. Aimed to understand how land use change affects the soil CO2 and CH4 fluxes, we measured surface gas fluxes, gas concentration gradient, and 13C signature in CH4 and soil organic matter in profiles in a transect in Xishuangbanna, including a rainforest site and three rubber plantation sites with age gradient. Gas fluxes were measured by static chamber method and open chamber respiration system. Soil gases were sampled from installed gas samplers at 5, 10, 30, and 75cm depth at representative time in dry and rainy season. The soil CO2 flux was comparable in rainforest and old rubber plantations, while young rubber plantation had the lowest rate. Total carbon content in the surface soil well explained the difference of soil CO2 flux between sites. All sites were CH4 sinks in dry season and uptake decreased in the order of rainforest, old rubber plantations and young rubber plantation. From dry season to rainy season, CH4 consumption decreased with increasing CH4 concentration in the soil profile at all depths. The enrichment of methane by 13CH4 shifted towards to lowerδ13C, being the evidence of enhanced CH4 production process while net surface methane flux reflected the consumption in wet condition. Increment of CH4 concentration in the profile from dry to rainy season was higher in old rubber plantation compared to rainforest, while the shifting of δ13CH4 was larger in rainforest than rubber sites. Turnover rates of soil CO2 and CH4 suggested that the 0-5 cm surface soil was the most active layer for gaseous carbon exchange. δ13C in soil organic matter and soil moisture increased from rainforest, young rubber plantation to old

Do plant species influence soil CO2 and N2O fluxes in a diverse tropical forest?

Science.gov (United States)

J.L.M. van Haren; R.C. de Oliveira; N. Restrepo-Coupe; L. Hutyra; P. B. de Camargo; Michael Keller; S.R. Saleska

2010-01-01

[1] To test whether plant species influence greenhouse gas production in diverse ecosystems, we measured wet season soil CO2 and N2O fluxes close to 300 large (>35 cm in diameter at breast height (DBH)) trees of 15 species at three clay‐rich forest sites in central Amazonia. We found that soil CO2 fluxes were 38% higher near large trees than at control sites >10...

Environmental controls of temporal and spatial variability in CO2 and CH4 fluxes in a neotropical peatland.

Science.gov (United States)

Wright, Emma L; Black, Colin R; Turner, Benjamin L; Sjögersten, Sofie

2013-12-01

Tropical peatlands play an important role in the global storage and cycling of carbon (C) but information on carbon dioxide (CO2) and methane (CH4) fluxes from these systems is sparse, particularly in the Neotropics. We quantified short and long-term temporal and small scale spatial variation in CO2 and CH4 fluxes from three contrasting vegetation communities in a domed ombrotrophic peatland in Panama. There was significant variation in CO2 fluxes among vegetation communities in the order Campnosperma panamensis > Raphia taedigera > Cyperus. There was no consistent variation among sites and no discernible seasonal pattern of CH4 flux despite the considerable range of values recorded (e.g. -1.0 to 12.6 mg m(-2) h(-1) in 2007). CO2 fluxes varied seasonally in 2007, being greatest in drier periods (300-400 mg m(-2) h(-1)) and lowest during the wet period (60-132 mg m(-2) h(-1)) while very high emissions were found during the 2009 wet period, suggesting that peak CO2 fluxes may occur following both low and high rainfall. In contrast, only weak relationships between CH4 flux and rainfall (positive at the C. panamensis site) and solar radiation (negative at the C. panamensis and Cyperus sites) was found. CO2 fluxes showed a diurnal pattern across sites and at the Cyperus sp. site CO2 and CH4 fluxes were positively correlated. The amount of dissolved carbon and nutrients were strong predictors of small scale within-site variability in gas release but the effect was site-specific. We conclude that (i) temporal variability in CO2 was greater than variation among vegetation communities; (ii) rainfall may be a good predictor of CO2 emissions from tropical peatlands but temporal variation in CH4 does not follow seasonal rainfall patterns; and (iii) diurnal variation in CO2 fluxes across different vegetation communities can be described by a Fourier model. © 2013 John Wiley & Sons Ltd.

Kinetics of CO(2) fluxes outgassing from champagne glasses in tasting conditions: the role of temperature.

Science.gov (United States)

Liger-Belair, Gérard; Villaume, Sandra; Cilindre, Clara; Jeandet, Philippe

2009-03-11

Measurements of CO(2) fluxes outgassing from a flute poured with a standard Champagne wine initially holding about 11 g L(-1) of dissolved CO(2) were presented, in tasting conditions, all along the first 10 min following the pouring process. Experiments were performed at three sets of temperature, namely, 4 degrees C, 12 degrees C, and 20 degrees C, respectively. It was demonstrated that the lower the champagne temperature, the lower CO(2) volume fluxes outgassing from the flute. Therefore, the lower the champagne temperature, the lower its progressive loss of dissolved CO(2) concentration with time, which constitutes the first analytical proof that low champagne temperatures prolong the drink's chill and helps retains its effervescence. A correlation was also proposed between CO(2) volume fluxes outgassing from the flute poured with champagne and its continuously decreasing dissolved CO(2) concentration. Finally, the contribution of effervescence to the global kinetics of CO(2) release was discussed and modeled by the use of results developed over recent years. The temperature dependence of the champagne viscosity was found to play a major role in the kinetics of CO(2) outgassing from a flute. On the basis of this bubbling model, the theoretical influence of champagne temperature on CO(2) volume fluxes outgassing from a flute was discussed and found to be in quite good accordance with our experimental results.

The use of fair-weather cases from the ACT-America Summer 2016 field campaign to better constrain regional biogenic CO2 surface fluxes

Science.gov (United States)

Gaudet, B. J.; Davis, K. J.; DiGangi, J. P.; Feng, S.; Hoffman, K.; Jacobson, A. R.; Lauvaux, T.; McGill, M. J.; Miles, N.; Pal, S.; Pauly, R.; Richardson, S.

2017-12-01

The Atmospheric Carbon and Transport - America (ACT-America) study is a multi-year NASA-funded project designed to increase our understanding of regional-scale greenhouse gas (GHG) fluxes over North America through aircraft, satellite, and tower-based observations. This is being accomplished through a series of field campaigns that cover three focus regions (Mid-Atlantic, Gulf Coast, and Midwest), and all four seasons (summer, winter, fall, and spring), as well as a variety of meteorological conditions. While constraints on GHG fluxes can be derived on the global scale (through remote-site concentration measurements and global flux inversion models) and the local scale (through eddy-covariance flux tower measurements), observational constraints on the intermediate scales are not as readily available. Biogenic CO2 fluxes are particularly challenging because of their strong seasonal and diurnal cycles and large spatial variability. During the summer 2016 ACT field campaign, fair weather days were targeted for special flight patterns designed to estimate surface fluxes at scales on the order of 105 km2 using a modified mass-balance approach. For some onshore flow cases in the Gulf Coast, atmospheric boundary layer (ABL) flight transects were performed both inland and offshore when it could be reasonably inferred that the homogeneous Gulf air provided the background GHG field for the inland transect. On other days, two-day flight sequences were performed, where the second-day location of the flight patterns was designed to encompass the air mass that was sampled on the first day. With these flight patterns, the average regional flux can be estimated from the ABL CO2 concentration change. Direct measurements of ABL depth from both aircraft profiles and high-resolution airborne lidar will be used, while winds and free-tropospheric CO2 can be determined from model output and in situ aircraft observations. Here we will present examples of this flux estimation for both Gulf

Human impact on the historical change of CO2 degassing flux in River Changjiang

Directory of Open Access Journals (Sweden)

Zhang Jing

2007-08-01

Full Text Available Abstract The impact of water quality changes in River Changjiang (formally known as the Yangtze River on dissolved CO2 and silicate concentrations and seasonal carbon flux in the past several decades (1960s–2000 was evaluated, based on monitoring data from hydrographic gauge. It was found that dissolved CO2 and silicate in Changjiang decreased dramatically during this decades, as opposed to a marked increase in nutrient (e.g. NO3- concentrations. Our analyses revealed that dissolved CO2 in Changjiang was over-saturated with the atmosphere CO2, and its concentration had showed a declining trend since the 1960s, despite that fluvial DIC flux had maintained stable. Analysis results also suggested that the decrease in dissolved CO2 concentration was attributed to changes on the riverine trophic level and river damming activities in the Changjiang drainage basin. Due to the economic innovation (e.g. agriculture and industry development across the Changjiang watershed, fertilizers application and river regulations have significantly altered the original state of the river. Its ecosystem and hydrological condition have been evolving toward the "lacustrine/reservoir" autotrophic type prevailing with plankton. Accordingly, average CO2 diffusing flux to the atmosphere from the river had been reduced by three-fourth from the 1960s to 1990s, with the flux value being down to 14.2 mol.m-2.yr-1 in the 1990s. For a rough estimate, approximately 15.3 Mt of carbon was degassed annually into the atmosphere from the entire Changjiang drainage basin in the 1990s.

Particle fluxes above forests: Observations, methodological considerations and method comparisons

International Nuclear Information System (INIS)

Pryor, S.C.; Larsen, S.E.; Sorensen, L.L.; Barthelmie, R.J.

2008-01-01

This paper reports a study designed to test, evaluate and compare micro-meteorological methods for determining the particle number flux above forest canopies. Half-hour average particle number fluxes above a representative broad-leaved forest in Denmark derived using eddy covariance range from -7 x 10 7 m -2 s -1 (1st percentile) to 5 x 10 7 m -2 s -1 (99th percentile), and have a median value of -1.6 x 10 6 m -2 s -1 . The statistical uncertainties associated with the particle number flux estimates are larger than those for momentum fluxes and imply that in this data set approximately half of the particle number fluxes are not statistically different to zero. Particle number fluxes from relaxed eddy accumulation (REA) and eddy covariance are highly correlated and of almost identical magnitude. Flux estimates from the co-spectral and dissipation methods are also correlated with those from eddy covariance but exhibit higher absolute magnitude of fluxes. - Number fluxes of ultra-fine particles over a forest computed using four micro-meteorological techniques are highly correlated but vary in magnitude

Nonlinear CO2 flux response to 7 years of experimentally induced permafrost thaw.

Science.gov (United States)

Mauritz, Marguerite; Bracho, Rosvel; Celis, Gerardo; Hutchings, Jack; Natali, Susan M; Pegoraro, Elaine; Salmon, Verity G; Schädel, Christina; Webb, Elizabeth E; Schuur, Edward A G

2017-09-01

Rapid Arctic warming is expected to increase global greenhouse gas concentrations as permafrost thaw exposes immense stores of frozen carbon (C) to microbial decomposition. Permafrost thaw also stimulates plant growth, which could offset C loss. Using data from 7 years of experimental Air and Soil warming in moist acidic tundra, we show that Soil warming had a much stronger effect on CO 2 flux than Air warming. Soil warming caused rapid permafrost thaw and increased ecosystem respiration (R eco ), gross primary productivity (GPP), and net summer CO 2 storage (NEE). Over 7 years R eco , GPP, and NEE also increased in Control (i.e., ambient plots), but this change could be explained by slow thaw in Control areas. In the initial stages of thaw, R eco , GPP, and NEE increased linearly with thaw across all treatments, despite different rates of thaw. As thaw in Soil warming continued to increase linearly, ground surface subsidence created saturated microsites and suppressed R eco , GPP, and NEE. However R eco and GPP remained high in areas with large Eriophorum vaginatum biomass. In general NEE increased with thaw, but was more strongly correlated with plant biomass than thaw, indicating that higher R eco in deeply thawed areas during summer months was balanced by GPP. Summer CO 2 flux across treatments fit a single quadratic relationship that captured the functional response of CO 2 flux to thaw, water table depth, and plant biomass. These results demonstrate the importance of indirect thaw effects on CO 2 flux: plant growth and water table dynamics. Nonsummer R eco models estimated that the area was an annual CO 2 source during all years of observation. Nonsummer CO 2 loss in warmer, more deeply thawed soils exceeded the increases in summer GPP, and thawed tundra was a net annual CO 2 source. © 2017 John Wiley & Sons Ltd.

Combining sap flow and eddy covariance approaches to derive stomatal and non-stomatal O3 fluxes in a forest stand

International Nuclear Information System (INIS)

Nunn, A.J.; Cieslik, S.; Metzger, U.; Wieser, G.; Matyssek, R.

2010-01-01

Stomatal O 3 fluxes to a mixed beech/spruce stand (Fagus sylvatica/Picea abies) in Central Europe were determined using two different approaches. The sap flow technique yielded the tree-level transpiration, whereas the eddy covariance method provided the stand-level evapotranspiration. Both data were then converted into stomatal ozone fluxes, exemplifying this novel concept for July 2007. Sap flow-based stomatal O 3 flux was 33% of the total O 3 flux, whereas derivation from evapotranspiration rates in combination with the Penman-Monteith algorithm amounted to 47%. In addition to this proportional difference, the sap flow-based assessment yielded lower levels of stomatal O 3 flux and reflected stomatal regulation rather than O 3 exposure, paralleling the daily courses of canopy conductance for water vapor and eddy covariance-based total stand-level O 3 flux. The demonstrated combination of sap flow and eddy covariance approaches supports the development of O 3 risk assessment in forests from O 3 exposure towards flux-based concepts. - Combined tree sap flow and eddy covariance-based methodologies yield stomatal O 3 flux as 33% in total stand flux.

Variability and budget of CO2 in Europe: analysis of the CAATER airborne campaigns – Part 2: Comparison of CO2 vertical variability and fluxes between observations and a modeling framework

Directory of Open Access Journals (Sweden)

P. Ciais

2011-06-01

Full Text Available Our ability to predict future climate change relies on our understanding of current and future CO2 fluxes, particularly on a regional scale (100–1000 km. CO2 regional sources and sinks are still poorly understood. Inverse transport modeling, a method often used to quantify these fluxes, relies on atmospheric CO2 measurements. One of the main challenges for the transport models used in the inversions is to properly reproduce CO2 vertical gradients between the boundary layer and the free troposphere, as these gradients impact on the partitioning of the calculated fluxes between the different model regions. Vertical CO2 profiles are very well suited to assess the performances of the models. In this paper, we conduct a comparison between observed and modeled CO2 profiles recorded during two CAATER campaigns that occurred in May 2001 and October 2002 over Western Europe, as described in a companion paper. We test different combinations between a global transport model (LMDZt, a mesoscale transport model (CHIMERE, and different sets of biospheric fluxes, all chosen with a diurnal cycle (CASA, SiB2 and ORCHIDEE. The vertical profile comparison shows that: 1 in most cases the influence of the biospheric flux is small but sometimes not negligible, ORCHIDEE giving the best results in the present study; 2 LMDZt is most of the time too diffuse, as it simulates a too high boundary layer height; 3 CHIMERE better reproduces the observed gradients between the boundary layer and the free troposphere, but is sometimes too variable and gives rise to incoherent structures. We conclude there is a need for more vertical profiles to conduct further studies to improve the parameterization of vertical transport in the models used for CO2 flux inversions. Furthermore, we use a modeling method to quantify CO2 fluxes at the regional scale from a chosen observing point, coupling influence functions from the transport model LMDZt (that works quite well at the synoptic

Seasonal variability of soil CO2 flux and its carbon isotope composition in Krakow urban area, Southern Poland.

Science.gov (United States)

Jasek, Alina; Zimnoch, Miroslaw; Gorczyca, Zbigniew; Smula, Ewa; Rozanski, Kazimierz

2014-06-01

As urban atmosphere is depleted of (13)CO2, its imprint should be detectable in the local vegetation and therefore in its CO2 respiratory emissions. This work was aimed at characterising strength and isotope signature of CO2 fluxes from soil in urban areas with varying distances from anthropogenic CO2 emissions. The soil CO2 flux and its δ(13)C isotope signature were measured using a chamber method on a monthly basis from July 2009 to May 2012 within the metropolitan area of Krakow, Southern Poland, at two locations representing different levels of anthropogenic influence: a lawn adjacent to a busy street (A) and an urban meadow (B). The small-scale spatial variability of the soil CO2 flux was also investigated at site B. Site B revealed significantly higher summer CO2 fluxes (by approximately 46 %) than site A, but no significant differences were found between their δ(13)CO2 signatures.

Methane and carbon dioxide fluxes and source partitioning in urban areas: The case study of Florence, Italy

International Nuclear Information System (INIS)

Gioli, B.; Toscano, P.; Lugato, E.; Matese, A.; Miglietta, F.; Zaldei, A.; Vaccari, F.P.

2012-01-01

Long-term fluxes of CO 2 , and combined short-term fluxes of CH 4 and CO 2 were measured with the eddy covariance technique in the city centre of Florence. CO 2 long-term weekly fluxes exhibit a high seasonality, ranging from 39 to 172% of the mean annual value in summer and winter respectively, while CH 4 fluxes are relevant and don’t exhibit temporal variability. Contribution of road traffic and domestic heating has been estimated through multi-regression models combined with inventorial traffic and CH 4 consumption data, revealing that heating accounts for more than 80% of observed CO 2 fluxes. Those two components are instead responsible for only 14% of observed CH 4 fluxes, while the major residual part is likely dominated by gas network leakages. CH 4 fluxes expressed as CO 2 equivalent represent about 8% of CO 2 emissions, ranging from 16% in summer to 4% in winter, and cannot therefore be neglected when assessing greenhouse impact of cities. - Highlights: ► CH 4 and CO 2 fluxes were measured with eddy covariance in Florence city centre. ► CO 2 fluxes are dominated by winter time domestic heating combustion. ► Natural gas network leakages are responsible for 85% of observed methane emissions. ► Greenhouse impact of CH 4 accounts for 8% of CO 2 emissions. - GHG flux measurements in Florence city revealed that domestic heating and gas network leakages are the predominant contributions to CO 2 and CH 4 emissions, respectively.

Measuring the Effects of Disturbance & Climate on the CO2 & Energy Exchange of Ponderosa Pine Forests in the Pacific Northwest: Integration of Eddy Flux, Plant and Soil Measurements

Energy Technology Data Exchange (ETDEWEB)

Beverly E. Law; Larry Mahrt

2007-01-05

The goal is to quantify and understand the influence of climate and disturbance on ecosystem processes and thus net carbon uptake by forests. The objective is to combine tower and ground-based observations to quantify the effects of disturbance on processes controlling carbon storage and CO{sub 2} and energy exchange in varying climatic conditions. Specific objectives are: (1) Investigate the effects of logging and fire on carbon storage and carbon dioxide and energy exchange in chronosequences of ponderosa pine, using consistent methodology; (2) Determine key environmental factors controlling carbon storage and carbon dioxide and energy exchange in these forests through a combination of measurements and process modeling; and (3) Assess spatial variation of the concentrations and transport in complex terrain. The eddy covariance method is used for measurements of CO2, water vapor, and energy exchanges in a chronosequence of ponderosa pine forests (burned in 2002 wildfire, 10 year-old stand, 90 year-old mature stand). The mature stand has been an AmeriFlux site since 2000 (following previous flux sites in young and old stands initiated in 1996). In addition to the eddy covariance measurements, a large suite of biological processes and ecosystem properties are determined for the purpose of developing independent forest carbon budgets and NEP estimates; these include photosynthesis, stand respiration, soil CO{sub 2} fluxes, annual litterfall, foliar chemistry, and bole increment, and soil organic matter among other parameters. The measurements are being integrated and evaluated with two ecosystem models (BIOME-BGC and SPA). Such analyses are needed to assess regional terrestrial ecosystem carbon budgets. The results will contribute scientific understanding of carbon processes, and will provide comprehensive data sets for forest managers and those preparing national carbon inventories to use in assessments of carbon sequestration in relation to interannual climate

Simulating dynamics of {delta}{sup 13}C of CO{sub 2} in the planetary boundary layer a boreal forest region: covariation between surface fluxes and atmospheric mixing

Energy Technology Data Exchange (ETDEWEB)

Chen, Baozhang; Chen, Jing M. [Univ. of Toronto, ON (Canada). Dept. of Geography; Tans, Pieter P. [National Oceanic and Atmospheric Administration, Boulder, CO (United States). Earth System Research Lab.; Huang, Lin [Environment Canada, Toronto, ON (Canada). Atmospheric Science and Technology Directorate

2006-11-15

Stable isotopes of CO{sub 2} contain unique information on the biological and physical processes that exchange CO{sub 2} between terrestrial ecosystems and the atmosphere. Ecosystem exchange of carbon isotopes with the atmosphere is correlated diurnally and seasonally with the planetary boundary layer (PBL) dynamics. The strength of this kind of covariation affects the vertical gradient of {delta}{sup 13}C and thus the global {delta}{sup 13}C distribution pattern. We need to understand the various processes involved in transport/diffusion of carbon isotope ratio in the PBL and between the PBL and the biosphere and the troposphere. In this study, we employ a one-dimensional vertical diffusion/transport atmospheric model (VDS), coupled to an ecosystem isotope model (BEPS-EASS) to simulate dynamics of {sup 13}CO{sub 2} in the PBL over a boreal forest region in the vicinity of the Fraserdale (FRD) tower (49 deg 52 min 29.9 sec N, 81 deg 34 min 12.3 sec W) in northern Ontario, Canada. The data from intensive campaigns during the growing season in 1999 at this site are used for model validation in the surface layer. The model performance, overall, is satisfactory in simulating the measured data over the whole course of the growing season. We examine the interaction of the biosphere and the atmosphere through the PBL with respect to {delta}{sup 13}C on diurnal and seasonal scales. The simulated annual mean vertical gradient of {delta}{sup 13}C in the PBL in the vicinity of the FRD tower was about 0.025% in 1999. The {delta}{sup 13}C vertical gradient exhibited strong diurnal (29%) and seasonal (71%) variations that do not exactly mimic those of CO{sub 2}. Most of the vertical gradient (96.5% {+-}) resulted from covariation between ecosystem exchange of carbon isotopes and the PBL dynamics, while the rest (3.5%{+-}) was contributed by isotopic disequilibrium between respiration and photosynthesis. This disequilibrium effect on {delta}{sup 13}C of CO{sub 2} dynamics in PBL

Simulating dynamics of (delta){sup 13}C of CO{sub 2} in the planetary boundary layer a boreal forest region: covariation between surface fluxes and atmospheric mixing

Energy Technology Data Exchange (ETDEWEB)

Chen, Baozhang; Chen, Jing M. [Univ. of Toronto, ON (Canada). Dept. of Geography; Tans, Pieter P. [National Oceanic and Atmospheric Administration, Boulder, CO (United States). Earth System Research Lab.; Huang, Lin [Environment Canada, Toronto, ON (Canada). Atmospheric Science and Technology Directorate

2006-11-15

Stable isotopes of CO{sub 2} contain unique information on the biological and physical processes that exchange CO{sub 2} between terrestrial ecosystems and the atmosphere. Ecosystem exchange of carbon isotopes with the atmosphere is correlated diurnally and seasonally with the planetary boundary layer (PBL) dynamics. The strength of this kind of covariation affects the vertical gradient of (delta){sup 13}C and thus the global (delta){sup 13}C distribution pattern. We need to understand the various processes involved in transport/diffusion of carbon isotope ratio in the PBL and between the PBL and the biosphere and the troposphere. In this study, we employ a one-dimensional vertical diffusion/transport atmospheric model (VDS), coupled to an ecosystem isotope model (BEPS-EASS) to simulate dynamics of {sup 13}CO{sub 2} in the PBL over a boreal forest region in the vicinity of the Fraserdale (FRD) tower (49 deg 52 min 29.9 sec N, 81 deg 34 min 12.3 sec W) in northern Ontario, Canada. The data from intensive campaigns during the growing season in 1999 at this site are used for model validation in the surface layer. The model performance, overall, is satisfactory in simulating the measured data over the whole course of the growing season. We examine the interaction of the biosphere and the atmosphere through the PBL with respect to (delta){sup 13}C on diurnal and seasonal scales. The simulated annual mean vertical gradient of (delta){sup 13}C in the PBL in the vicinity of the FRD tower was about 0.025% in 1999. The (delta){sup 13}C vertical gradient exhibited strong diurnal (29%) and seasonal (71%) variations that do not exactly mimic those of CO{sub 2}. Most of the vertical gradient (96.5% {+-}) resulted from covariation between ecosystem exchange of carbon isotopes and the PBL dynamics, while the rest (3.5%{+-}) was contributed by isotopic disequilibrium between respiration and photosynthesis. This disequilibrium effect on (delta){sup 13}C of CO{sub 2} dynamics in PBL

Air-water gas exchange and CO2 flux in a mangrove-dominated estuary

Science.gov (United States)

Ho, David T.; Ferrón, Sara; Engel, Victor C.; Larsen, Laurel G.; Barr, Jordan G.

2014-01-01

Mangrove forests are highly productive ecosystems, but the fate of mangrove-derived carbon remains uncertain. Part of that uncertainty stems from the fact that gas transfer velocities in mangrove-surrounded waters are not well determined, leading to uncertainty in air-water CO2 fluxes. Two SF6 tracer release experiments were conducted to determine gas transfer velocities (k(600) = 8.3 ± 0.4 and 8.1 ± 0.6 cm h−1), along with simultaneous measurements of pCO2 to determine the air-water CO2 fluxes from Shark River, Florida (232.11 ± 23.69 and 171.13 ± 20.28 mmol C m−2 d−1), an estuary within the largest contiguous mangrove forest in North America. The gas transfer velocity results are consistent with turbulent kinetic energy dissipation measurements, indicating a higher rate of turbulence and gas exchange than predicted by commonly used wind speed/gas exchange parameterizations. The results have important implications for carbon fluxes in mangrove ecosystems.

Potential for negative emissions of greenhouse gases (CO2, CH4 and N2O) through coastal peatland re-establishment: Novel insights from high frequency flux data at meter and kilometer scales

Science.gov (United States)

Windham-Myers, Lisamarie; Bergamaschi, Brian; Anderson, Frank; Knox, Sara; Miller, Robin; Fujii, Roger

2018-04-01

High productivity temperate wetlands that accrete peat via belowground biomass (peatlands) may be managed for climate mitigation benefits due to their global distribution and notably negative emissions of atmospheric carbon dioxide (CO2) through rapid storage of carbon (C) in anoxic soils. Net emissions of additional greenhouse gases (GHG)—methane (CH4) and nitrous oxide (N2O)—are more difficult to predict and monitor due to fine-scale temporal and spatial variability, but can potentially reverse the climate mitigation benefits resulting from CO2 uptake. To support management decisions and modeling, we collected continuous 96 hour high frequency GHG flux data for CO2, CH4 and N2O at multiple scales—static chambers (1 Hz) and eddy covariance (10 Hz)—during peak productivity in a well-studied, impounded coastal peatland in California’s Sacramento Delta with high annual rates of C fluxes, sequestering 2065 ± 150 g CO2 m‑2 y‑1 and emitting 64.5 ± 2.4 g CH4 m‑2 y‑1. Chambers (n = 6) showed strong spatial variability along a hydrologic gradient from inlet to interior plots. Daily (24 hour) net CO2 uptake (NEE) was highest near inlet locations and fell dramatically along the flowpath (‑25 to ‑3.8 to +2.64 g CO2 m‑2 d‑1). In contrast, daily net CH4 flux increased along the flowpath (0.39 to 0.62 to 0.88 g CH4 m‑2 d‑1), such that sites of high daily CO2 uptake were sites of low CH4 emission. Distributed, continuous chamber data exposed five novel insights, and at least two important datagaps for wetland GHG management, including: (1) increasing dominance of CH4 ebullition fluxes (15%–32% of total) along the flowpath and (2) net negative N2O flux across all sites as measured during a 4 day period of peak biomass (‑1.7 mg N2O m‑2 d‑1 0.51 g CO2 eq m‑2 d‑1). The net negative emissions of re-established peat-accreting wetlands are notably high, but may be poorly estimated by

Ground-Based Remote Sensing of Volcanic CO2 Fluxes at Solfatara (Italy—Direct Versus Inverse Bayesian Retrieval

Directory of Open Access Journals (Sweden)

Manuel Queißer

2018-01-01

Full Text Available CO2 is the second most abundant volatile species of degassing magma. CO2 fluxes carry information of incredible value, such as periods of volcanic unrest. Ground-based laser remote sensing is a powerful technique to measure CO2 fluxes in a spatially integrated manner, quickly and from a safe distance, but it needs accurate knowledge of the plume speed. The latter is often difficult to estimate, particularly for complex topographies. So, a supplementary or even alternative way of retrieving fluxes would be beneficial. Here, we assess Bayesian inversion as a potential technique for the case of the volcanic crater of Solfatara (Italy, a complex terrain hosting two major CO2 degassing fumarolic vents close to a steep slope. Direct integration of remotely sensed CO2 concentrations of these vents using plume speed derived from optical flow analysis yielded a flux of 717 ± 121 t day−1, in agreement with independent measurements. The flux from Bayesian inversion based on a simple Gaussian plume model was in excellent agreement under certain conditions. In conclusion, Bayesian inversion is a promising retrieval tool for CO2 fluxes, especially in situations where plume speed estimation methods fail, e.g., optical flow for transparent plumes. The results have implications beyond volcanology, including ground-based remote sensing of greenhouse gases and verification of satellite soundings.

Soil CO 2 fluxes from direct seeding rice fields under two tillage practices in central China

Science.gov (United States)

Li, Cheng-fang; Kou, Zhi-kui; Yang, Jin-hua; Cai, Ming-li; Wang, Jin-ping; Cao, Cou-gui

2010-07-01

Agricultural practices affect the production and emission of carbon dioxide (CO 2) from paddy soils. It is crucial to understand the effects of tillage and N fertilization on soil CO 2 flux and its influencing factors for a better comprehension of carbon dynamics in subtropical paddy ecosystems. A 2-yr field study was conducted to assess the effects of tillage (conventional tillage [CT] and no-tillage [NT]) and N fertilization (0 and 210 kg N ha -1) on soil CO 2 fluxes during the 2008 and 2009 rice growing seasons in central China. Treatments were established following a split-plot design of a randomized complete block with tillage practices as the main plot and N fertilizer level as the split-plot treatment. The soil CO 2 fluxes were measured 24 times in 2008 and 17 times in 2009. N fertilization did not affect soil CO 2 emissions while tillage affected soil CO 2 emissions, where NT had similar soil CO 2 emissions to CT in 2008, but in 2009, NT significantly increased soil CO 2 emissions. Cumulative CO 2 emissions were 2079-2245 kg CO 2-C ha -1 from NT treatments, and 2084-2141 kg CO 2-C ha -1 from CT treatments in 2008, and were 1257-1401 kg CO 2-C ha -1 from NT treatments, and 1003-1034 kg CO 2-C ha -1 from CT treatments in 2009, respectively. Cumulative CO 2 emissions were significantly related to aboveground biomass and soil organic C. Before drainage of paddy fields, soil CO 2 fluxes were significantly related to soil temperature with correlation coefficients ( R) of 0.67-0.87 in 2008 and 0.69-0.85 in 2009; moreover, the Q 10 values ranged from 1.28 to 1.55 and from 2.10 to 5.21 in 2009, respectively. Our results suggested that NT rice production system appeared to be ineffective in decreasing carbon emission, which suggested that CO 2 emissions from integrated rice-based system should be taken into account to assess effects of tillage.

[Effects of biological soil crust at different succession stages in hilly region of Loess Plateau on soil CO2 flux].

Science.gov (United States)

Wang, Ai-Guo; Zhao, Yun-Ge; Xu, Ming-Xiang; Yang, Li-Na; Ming, Jiao

2013-03-01

Biological soil crust (biocrust) is a compact complex layer of soil, which has photosynthetic activity and is one of the factors affecting the CO2flux of soil-atmosphere interface. In this paper, the soil CO, flux under the effects of biocrust at different succession stages on the re-vegetated grassland in the hilly region of Loess Plateau was measured by a modified LI-8100 automated CO, flux system. Under light condition, the soil CO2 flux under effects of cyanobacteria crust and moss crust was significantly decreased by 92% and 305%, respectively, as compared with the flux without the effects of the biocrusts. The decrement of the soil CO, flux by the biocrusts was related to the biocrusts components and their biomass. Under the effects of dark colored cyanobacteria crust and moss crust, the soil CO2 flux was decreased by 141% and 484%, respectively, as compared with that in bare land. The diurnal curve of soil CO2 flux under effects of biocrusts presented a trend of 'drop-rise-drop' , with the maximum carbon uptake under effects of cyanobacteria crust and moss crust being 0.13 and -1.02 micromol CO2.m-2.s-1 and occurred at about 8:00 and 9:00 am, respectively, while that in bare land was unimodal. In a day (24 h) , the total CO2 flux under effects of cyanobacteria crust was increased by 7.7% , while that under effects of moss crust was decreased by 29.6%, as compared with the total CO2 flux in bare land. This study suggested that in the hilly region of Loess Plateau, biocrust had significant effects on soil CO2 flux, which should be taken into consideration when assessing the carbon budget of the 'Grain for Green' eco-project.

Diffuse CO2 fluxes from Santiago and Congro volcanic lakes (São Miguel, Azores archipelago)

Science.gov (United States)

Andrade, César; Cruz, José; Viveiros, Fátima; Branco, Rafael

2017-04-01

Diffuse CO2 degassing occurring in Santiago and Congro lakes, both located in depressions associated to maars from São Miguel Island (Azores, Portugal), was studied through detailed flux measurements. Four sampling campaigns were developed between 2013 and 2016 in each water body, split by the cold and wet seasons. São Miguel has an area of 744.6 km2, being the largest island of the archipelago. The geology of the island is dominated by three quiescent central volcanoes (Sete Cidades, Fogo and Furnas), linked by volcanic fissural zones (Picos and Congro Fissural Volcanic systems). The oldest volcanic systems of the island are located in its eastern part (Povoação-Nordeste). Santiago lake, with a surface area of 0.26 km2 and a depth of 30.5 m, is located inside a maar crater in the Sete Cidades volcano at an altitude of 355 m. The watershed of the lake has an area of 0.97 km2 and a surface flow estimated as 1.54x10 m3/a. A total of 1612 CO2 flux measurements using the accumulation chamber method were made at Santiago lake, 253 in the first campaign (November 2013), and 462, 475 and 422 in the three other campaigns, respectively, in April 2014, September 2016 and December 2016. The total CO2 flux estimated for this lake varies between 0.4 t d-1 and 0.59 t d-1, for the surveys performed, respectively, in November 2013 and September 2016; higher CO2 outputs of 1.57 and 5.87 t d-1 were calculated for the surveys carried out in April 2014 and December 2016. These higher CO2 emissions were associated with a period without water column stratification. Similarly to Santiago lake, Congro lake is located inside a maar, in the Congro Fissural Volcanic system, and has a surface area of 0.04 km2 with 18.5 m depth and a storage of about 2.4x105 m3/a. The lake, located at an altitude of 420 m, is fed by a watershed with an area of 0.33 km2 and a runoff estimated as about 8x104 m3/a. In Congro lake a total of 713 CO2 flux measurements were performed during four surveys from

Sensitivity of spectral indices to CO2 fluxes for several plant communities in a Sphagnum-dominated peatland

International Nuclear Information System (INIS)

Letendre, J.; Poulin, M.; Rochefort, L.

2008-01-01

A study was conducted in which the relationship between spectral indices and carbon dioxide (CO 2 ) fluxes was tested for different communities in a Sphagnum-dominated peatland. This paper focused on the remote sensing approach that was used to directly link spectral indices to CO 2 fluxes to highlight the potential of remote sensing for mapping the spatial distribution of CO 2 fluxes. Carbon exchange in these ecosystems has become an environmental concern since peatlands play a key role in the global carbon cycle. A portable climate-controlled chamber was used to measure fluxes while simultaneously recording reflectance with a hand-held spectroradiometer. A laboratory experiment was also conducted to find a water-related index that most correlated with Sphagnum water content in order to regulate the normalized difference vegetation index (NDVI) values obtained in the field. The laboratory experiment showed a strong correlation between Sphagnum water content and all spectral indices, notably the water index (WI), normalized difference water index (NDWI), and relative depth index (RDI). The water index was chosen to regulate NDVI values. This paper described the indices that were tested in the field for CO 2 flux estimations. NDVI alone was found to be a poor predictor of net ecosystem exchange. The relationship between CO 2 fluxes and narrow band chlorophyll indices was reasonably well adjusted. It was concluded that the chlorophyll indices may be the most promising for mapping the spatial distribution of CO 2 fluxes in the future. 62 refs., 2 tabs., 4 figs

Ecosystem Warming Affects CO2 Flux in an Agricultural Soil

Science.gov (United States)

Global warming seems likely based on present-day climate predictions. Our objective was to characterize and quantify the interactive effects of ecosystem warming (i.e., canopy temperature, TS), soil moisture content ('S) and microbial biomass (BM: bacteria, fungi) on the intra-row soil CO2 flux (FS)...

Estimation of CO2 flux from targeted satellite observations: a Bayesian approach

International Nuclear Information System (INIS)

Cox, Graham

2014-01-01

We consider the estimation of carbon dioxide flux at the ocean–atmosphere interface, given weighted averages of the mixing ratio in a vertical atmospheric column. In particular we examine the dependence of the posterior covariance on the weighting function used in taking observations, motivated by the fact that this function is instrument-dependent, hence one needs the ability to compare different weights. The estimation problem is considered using a variational data assimilation method, which is shown to admit an equivalent infinite-dimensional Bayesian formulation. The main tool in our investigation is an explicit formula for the posterior covariance in terms of the prior covariance and observation operator. Using this formula, we compare weighting functions concentrated near the surface of the earth with those concentrated near the top of the atmosphere, in terms of the resulting covariance operators. We also consider the problem of observational targeting, and ask if it is possible to reduce the covariance in a prescribed direction through an appropriate choice of weighting function. We find that this is not the case—there exist directions in which one can never gain information, regardless of the choice of weight. (paper)

Regional Scaling of Airborne Eddy Covariance Flux Observation

Science.gov (United States)

Sachs, T.; Serafimovich, A.; Metzger, S.; Kohnert, K.; Hartmann, J.

2014-12-01

The earth's surface is tightly coupled to the global climate system by the vertical exchange of energy and matter. Thus, to better understand and potentially predict changes to our climate system, it is critical to quantify the surface-atmosphere exchange of heat, water vapor, and greenhouse gases on climate-relevant spatial and temporal scales. Currently, most flux observations consist of ground-based, continuous but local measurements. These provide a good basis for temporal integration, but may not be representative of the larger regional context. This is particularly true for the Arctic, where site selection is additionally bound by logistical constraints, among others. Airborne measurements can overcome this limitation by covering distances of hundreds of kilometers over time periods of a few hours. The Airborne Measurements of Methane Fluxes (AIRMETH) campaigns are designed to quantitatively and spatially explicitly address this issue: The research aircraft POLAR 5 is used to acquire thousands of kilometers of eddy-covariance flux data. During the AIRMETH-2012 and AIRMETH-2013 campaigns we measured the turbulent exchange of energy, methane, and (in 2013) carbon dioxide over the North Slope of Alaska, USA, and the Mackenzie Delta, Canada. Here, we present the potential of environmental response functions (ERFs) for quantitatively linking flux observations to meteorological and biophysical drivers in the flux footprints. We use wavelet transforms of the original high-frequency data to improve spatial discretization of the flux observations. This also enables the quantification of continuous and biophysically relevant land cover properties in the flux footprint of each observation. A machine learning technique is then employed to extract and quantify the functional relationships between flux observations and the meteorological and biophysical drivers. The resulting ERFs are used to extrapolate fluxes over spatio-temporally explicit grids of the study area. The

Effect of Wildfire on Sequoiadendron giganteum Growth and CO2 Flux

Science.gov (United States)

Barwegen, S.

2016-12-01

Due to global warming, parts of the United States are becoming drier than ever before. In 2015, we surpassed 9 million acres burned by wildfires nationally (Rice 2015). Wildfires are most common in the Western United States due to drought, and the fact that the summer months are drier than other areas such as the East Coast, so there is a higher risk for wildland fires (Donegan 2016). These high-growth forests that are more frequently burned by wildfires each year are located near mountain ranges on the west side of the United States. They are important to tourism, contain many endangered species, and need to maintain the natural cycle of fire and regrowth for the continued success of the native plant life. This project investigated the effect of burnt soil on Sequoiadendron giganteum trees. Three were grown in burnt potting soil that had been roasted over a grill for 45 minutes (which is the average destructive fire time), and the other three were the control group in unburned potting soil. We assessed growth by measuring height, color, photosynthetically active radiation (PAR), and CO2 flux to evaluate the health of the trees in the two soil conditions. We noted that after two weeks the trunks of the trees growing in burnt soil began to brown in color, and they lost leaves. Over the course of the experiment, the trees growing in burnt soil had reduced levels of photosynthesis as compared to the unburned soil (as measured by the net change in CO2 concentration in a sealed chamber over the course of fifteen minutes intervals). On average, the trees growing in burnt soil had flux rates that were 19.59 ppm CO2 /min. more than those growing in unburned soil. In the dark reactions, the burnt soil flux was 54.5 ppm CO2/min., while the unburned soil averaged 40.5 ppm CO2/min. Our results help quantify the impact of fire on delicate ecosystems that are experiencing an increase in fire activity caused by global warming.

Eddy Covariance Fluxes of the NO-O3-NO2 Triad above the Forest Canopy at the ATTO Site in the Amazon Basin

Science.gov (United States)

Tsokankunku, A.; Wolff, S.; Berger, M.; Zelger, M.; Dlugi, R. J. W.; Andreae, M. O.; Sörgel, M.

2017-12-01

Nitrogen monoxide (NO) and nitrogen dioxide (NO2) (denoted together as NOx) determine the abundance of the tropospheric oxidants OH, O3 and NO3 that regulate atmospheric self-cleaning. The three reactive trace gases NO, NO2 and O3 undergo a series of interconnected photochemical reactions and are therefore often referred to as the NO-O3-NO2 triad. Ozone deposition is mainly controlled by stomatal uptake, therefore resulting in oxidative stress for the plants. Similarly, nitrogen dioxide from above or below the canopy is deposited to leaves through stomatal uptake. NO emissions from soils contribute to above canopy O3 formation and accelerate OH recycling. Therefore, quantification of the biosphere-atmosphere exchange fluxes of these species is important for atmospheric chemistry and ecosystem research. The eddy covariance method is state of the art for direct measurements of ecosystem fluxes of trace gases. Eddy covariance measurements of NOx in pristine environments are rare because of lack of availability of instruments with the required precision to resolve concentrations characteristic of these environments with the required high time resolution. The Amazon Tall Tower Observatory (ATTO) is located in a pristine rainforest environment in the Amazon basin about 150 km northeast of the city of Manaus. It is the ideal site for studying the biosphere-atmosphere exchange of the NO-O3-NO2 triad, because of the absence of nearby anthropogenic sources. During an intensive measurement campaign in November 2015 at the ATTO site, measurements of NO, NO2 and O3 were carried out at 42 m above ground level on the 80 m walk-up tower with a fast (5 Hz) and sensitive (< 30 ppt) instrument (CLD790SR2, Eco Physics) for NO and NO2 and with 10 Hz for O3 (Enviscope GmbH). Additionally, a suite of micrometeorological instruments was installed, including a profile of 3-dimensional sonic anemometers and meteorological sensors. Vertical concentration profile measurements of NO, NO2 and O

LBA-ECO TG-07 Soil CO2 Flux by Automated Chamber, Para, Brazil: 2001-2003

Science.gov (United States)

R.K. Varner; M.M. Keller

2009-01-01

Measurements of the soil-atmosphere flux of CO2 were made at the km 67 flux tower site in the Tapajos National Forest, Santarem, Para, Brazil. Eight chambers were set up to measure trace gas exchange between the soil and atmosphere about 5 times a day (during daylight and night) at this undisturbed forest site from April 2001 to April 2003. CO2 soil efflux data are...

BOREAS TGB-5 CO2, CH4 and CO Chamber Flux Data Over the NSA

Science.gov (United States)

Burke, Roger; Hall, Forrest G. (Editor); Conrad, Sara K. (Editor); Zepp, Richard

2000-01-01

The BOReal Ecosystem-Atmosphere Study Trace Gas Biogeochemistry (BOREAS TGB-5) team collected a variety of trace gas concentration and flux measurements at several NSA sites. This data set contains carbon dioxide (CO2), methane (CH4), and carbon monoxide (CO) chamber flux measurements conducted in 1994 at upland forest sites that experienced stand-replacement fires. These measurements were acquired to understand the impact of fires on soil biogeochemistry and related changes in trace gas exchange in boreal forest soils. Relevant ancillary data, including data concerning the soil temperature, solar irradiance, and information from nearby un-burned control sites, are included to provide a basis for modeling the regional impacts of fire and climate changes on trace gas biogeochemistry. The data are provided in tabular ASCII files.

Global CO2 flux inversions from remote-sensing data with systematic errors using hierarchical statistical models

Science.gov (United States)

Zammit-Mangion, Andrew; Stavert, Ann; Rigby, Matthew; Ganesan, Anita; Rayner, Peter; Cressie, Noel

2017-04-01

The Orbiting Carbon Observatory-2 (OCO-2) satellite was launched on 2 July 2014, and it has been a source of atmospheric CO2 data since September 2014. The OCO-2 dataset contains a number of variables, but the one of most interest for flux inversion has been the column-averaged dry-air mole fraction (in units of ppm). These global level-2 data offer the possibility of inferring CO2 fluxes at Earth's surface and tracking those fluxes over time. However, as well as having a component of random error, the OCO-2 data have a component of systematic error that is dependent on the instrument's mode, namely land nadir, land glint, and ocean glint. Our statistical approach to CO2-flux inversion starts with constructing a statistical model for the random and systematic errors with parameters that can be estimated from the OCO-2 data and possibly in situ sources from flasks, towers, and the Total Column Carbon Observing Network (TCCON). Dimension reduction of the flux field is achieved through the use of physical basis functions, while temporal evolution of the flux is captured by modelling the basis-function coefficients as a vector autoregressive process. For computational efficiency, flux inversion uses only three months of sensitivities of mole fraction to changes in flux, computed using MOZART; any residual variation is captured through the modelling of a stochastic process that varies smoothly as a function of latitude. The second stage of our statistical approach is to simulate from the posterior distribution of the basis-function coefficients and all unknown parameters given the data using a fully Bayesian Markov chain Monte Carlo (MCMC) algorithm. Estimates and posterior variances of the flux field can then be obtained straightforwardly from this distribution. Our statistical approach is different than others, as it simultaneously makes inference (and quantifies uncertainty) on both the error components' parameters and the CO2 fluxes. We compare it to more classical

Community metabolism and air-sea CO[sub 2] fluxes in a coral reef ecosystem (Moorea, French Polynesia)

Energy Technology Data Exchange (ETDEWEB)

Gattuso, J P; Pichon, M; Delesalle, B; Frankignoulle, M [Observatory of European Oceanology (Monaco)

1993-06-01

Community metabolism (primary production, respiration and calcification) and air-sea CO[sub 2] fluxes of the 'Tiahura barrier reef' (Moorea, French Polynesia) were investigated in November and December 1991. Gross production and respiration were respectively 640.2 to 753 and 590.4 to 641.5 mmol (O[sub 2] or CO[sub 2]) m[sup 2] d[sup -1] (7.7 to 9.0 and 7.1 to 7.7 g C m)[sup 2] d[sup -1] and the reef displayed a slightly negative excess (net) production. The contribution of planktonic primary production to reef metabolism was negligible (0.15% of total gross production). Net calcification was positive both during the day and at night; its daily value was 243 mmol CaCO[sub 3] m[sup 2] d[sup -1] (24.3 g CaCO)[sub 3] m[sup -2] d[sup -1]. Reef metabolism decreased seawater total CO[sub 2] by 433.3 mmol m[sup 2] d[sup -1]. The air-sea CO[sub 2] fluxes were close to zero in the ocean but displayed a strong daily pattern at the reef front and the back reef. Fluxes were positive (CO[sub 2] evasion) at night, decreased as irradiance increased and were negative during the day (CO[sub 2] invasion). Integration of the fluxes measured during a 24 h experiment at the back reef showed that the reef was a source of CO[sub 2] to the atmosphere (1.5 mmol m[sup 2] d[sup -1]).

Gully hotspot contribution to landscape methane (CH4) and carbon dioxide (CO2) fluxes in a northern peatland

International Nuclear Information System (INIS)

McNamara, N.P.; Plant, T.; Oakley, S.; Ward, S.; Wood, C.; Ostle, N.

2008-01-01

Peatlands are long term carbon catchments that sink atmospheric carbon dioxide (CO 2 ) and source methane (CH 4 ). In the uplands of the United Kingdom ombrotrophic blanket peatlands commonly exist within Calluna vulgaris (L.) dominated moorland ecosystems. These landscapes contain a range of topographical features that influence local hydrology, climate and plant community composition. In this study we examined the variation in ecosystem CO 2 respiration and net CH 4 fluxes from typical plant-soil systems in dendritic drainage gullies and adjacent blanket peat during the growing season. Typically, Eriophorum spp., Sphagnum spp. and mixed grasses occupied gullies while C. vulgaris dominated in adjacent blanket peat. Gross CO 2 respiration was highest in the areas of Eriophorum spp. (650 ± 140 mg CO 2 m -2 h -1 ) compared to those with Sphagnum spp. (338 ± 49 mg CO 2 m -2 h -1 ), mixed grasses (342 ± 91 mg CO 2 m -2 h -1 ) and C. vulgaris (174 ± 63 mg CO 2 m -2 h -1 ). Measurements of the net CH 4 flux showed higher fluxes from the Eriophorum spp (2.2 ± 0.6 mg CH 4 m -2 h -1 ) locations compared to the Sphagnum spp. (0.6 ± 0.4 mg CH 4 m -2 h -1 ), mixed grasses (0.1 ±0.1 mg CH 4 m -2 h -1 ) and a negligible flux detected from C. vulgaris (0.0 ± 0.0 mg CH 4 m -2 h -1 ) locations. A GIS approach was applied to calculate the contribution of gullies to landscape scale greenhouse gas fluxes. Findings from the Moor House National Nature Reserve in the UK showed that although gullies occupied only 9.3% of the total land surface, gullies accounted for 95.8% and 21.6% of the peatland net CH 4 and CO 2 respiratory fluxes, respectively. The implication of these findings is that the relative contribution of characteristic gully systems need to be considered in estimates of landscape scale peatland greenhouse gas fluxes

[Effects of fertilization on soil CO2 flux in Castanea mollissima stand].

Science.gov (United States)

Zhang, Jiao-Jiao; Li, Yong-Fu; Jiang, Pei-Kun; Zhou, Guo-Mo; Shen, Zhen-Ming; Liu, Juan; Wang, Zhan-Lei

2013-09-01

In June 2011-June 2012, a fertilization experiment was conducted in a typical Castanea mollissima stand in Lin' an of Zhejiang Province, East China to study the effects of inorganic and organic fertilization on the soil CO2 flux and the relationships between the soil CO2 flux and environmental factors. Four treatments were installed, i. e., no fertilization (CK), inorganic fertilization (IF), organic fertilization (OF), half organic plus half inorganic fertilization (OIF). The soil CO2 emission rate was determined by the method of static closed chamber/GC technique, and the soil temperature, soil moisture content, and soil water-soluble organic carbon (WSOC) concentration were determined by routine methods. The soil CO2 emission exhibited a strong seasonal pattern, with the highest rate in July or August and the lowest rate in February. The annual accumulative soil CO2 emission in CK was 27.7 t CO2 x hm(-2) x a(-1), and that in treatments IF, OF, and OIF was 29.5%, 47.0%, and 50.7% higher than the CK, respectively. The soil WSOC concentration in treatment IF (105.1 mg kg(-1)) was significantly higher than that in CK (76.6 mg x kg(-1)), but was obviously lower than that in treatments OF (133.0 mg x kg(-1)) and OIF (121.2 mg x kg(-1)). The temperature sensitivity of respiration (Q10) in treatments CK, IF, OF, and OIF was 1.47, 1.75, 1.49, and 1.57, respectively. The soil CO2 emission rate had significant positive correlations with the soil temperature at the depth of 5 cm and the soil WSOC concentration, but no significant correlation with soil moisture content. The increase of the soil WSOC concentration caused by fertilization was probably one of the reasons for the increase of soil CO2 emission from the C. mollissima stand.

Comparisons of a Quantum Annealing and Classical Computer Neural Net Approach for Inferring Global Annual CO2 Fluxes over Land

Science.gov (United States)

Halem, M.; Radov, A.; Singh, D.

2017-12-01

Investigations of mid to high latitude atmospheric CO2 show growing amplitudes in seasonal variations over the past several decades. Recent high-resolution satellite measurements of CO2 concentration are now available for three years from the Orbiting Carbon Observatory-2. The Atmospheric Radiation Measurement (ARM) program of DOE has been making long-term CO2-flux measurements (in addition to CO2 concentration and an array of other meteorological quantities) at several towers and mobile sites located around the globe at half-hour frequencies. Recent papers have shown CO2 fluxes inferred by assimilating CO2 observations into ecosystem models are largely inconsistent with station observations. An investigation of how the biosphere has reacted to changes in atmospheric CO2 is essential to our understanding of potential climate-vegetation feedbacks. Thus, new approaches for calculating CO2-flux for assimilation into land surface models are necessary for improving the prediction of annual carbon uptake. In this study, we calculate and compare the predicted CO2 fluxes results employing a Feed Forward Backward Propagation Neural Network model on two architectures, (i) an IBM Minsky Computer node and (ii) a hybrid version of the ARC D-Wave quantum annealing computer. We compare the neural net results of predictions of CO2 flux from ARM station data for three different DOE ecosystem sites; an arid plains near Oklahoma City, a northern arctic site at Barrows AL, and a tropical rainforest site in the Amazon. Training times and predictive results for the calculating annual CO2 flux for the two architectures for each of the three sites are presented. Comparative results of predictions as measured by RMSE and MAE are discussed. Plots and correlations of observed vs predicted CO2 flux are also presented for all three sites. We show the estimated training times for quantum and classical calculations when extended to calculating global annual Carbon Uptake over land. We also

Sensitivity of spectral indices to CO{sub 2} fluxes for several plant communities in a Sphagnum-dominated peatland

Energy Technology Data Exchange (ETDEWEB)

Letendre, J.; Poulin, M.; Rochefort, L. [Laval Univ., Quebec City, PQ (Canada). Dept. de Phytologie, Peatland Ecology and Research Group

2008-07-01

A study was conducted in which the relationship between spectral indices and carbon dioxide (CO{sub 2}) fluxes was tested for different communities in a Sphagnum-dominated peatland. This paper focused on the remote sensing approach that was used to directly link spectral indices to CO{sub 2} fluxes to highlight the potential of remote sensing for mapping the spatial distribution of CO{sub 2} fluxes. Carbon exchange in these ecosystems has become an environmental concern since peatlands play a key role in the global carbon cycle. A portable climate-controlled chamber was used to measure fluxes while simultaneously recording reflectance with a hand-held spectroradiometer. A laboratory experiment was also conducted to find a water-related index that most correlated with Sphagnum water content in order to regulate the normalized difference vegetation index (NDVI) values obtained in the field. The laboratory experiment showed a strong correlation between Sphagnum water content and all spectral indices, notably the water index (WI), normalized difference water index (NDWI), and relative depth index (RDI). The water index was chosen to regulate NDVI values. This paper described the indices that were tested in the field for CO{sub 2} flux estimations. NDVI alone was found to be a poor predictor of net ecosystem exchange. The relationship between CO{sub 2} fluxes and narrow band chlorophyll indices was reasonably well adjusted. It was concluded that the chlorophyll indices may be the most promising for mapping the spatial distribution of CO{sub 2} fluxes in the future. 62 refs., 2 tabs., 4 figs.

Effects of a holiday week on urban soil CO2 flux: an intensive study in Xiamen, southeastern China

Science.gov (United States)

Ye, H.; Wang, K.; Chen, F.

2012-12-01

To study the effects of a holiday period on urban soil CO2 flux, CO2 efflux from grassland soil in a traditional park in the city of Xiamen was measured hourly from 28th Sep to 11th Oct, a period that included China's National Day holiday week in 2009. The results of this study revealed that: a) The urban soil CO2 emissions were higher before and after the holiday week and lower during the National Day holiday reflecting changes in the traffic cycles; b) A diurnal cycle where the soil CO2 flux decreased from early morning to noon was associated with CO2 uptake by vegetation which strongly offset vehicle CO2 emissions. The soil CO2 flux increased from night to early morning, associated with reduced CO2 uptake by vegetation; c) During the National Day holiday week in 2009, lower rates of soil respiration were measured after Mid-Autumn Day than earlier in the week, and this was related to a reduced level of human activities and vehicle traffic, reducing the CO2 concentration in the air. Urban holidays have a clear effect on soil CO2 flux through the interactions between vehicle, visitor and vegetation CO2 emissions which indirectly control the use of carbon by plant roots, the rhizosphere and soil microorganisms. Consequently, appropriate traffic controls and tourism travel plans can have positive effects on the soil carbon store and may improve local air quality.

Seasonal and Intra-annual Controls on CO₂ Flux in Arctic Alaska

Energy Technology Data Exchange (ETDEWEB)

Oechel, Walter [San Diego State Univ., CA (United States); Kalhori, Aram [San Diego State Univ., CA (United States)

2015-12-01

In order to advance the understanding of the patterns and controls on the carbon budget in the Arctic region, San Diego State University has maintained eddy covariance flux towers at three sites in Arctic Alaska, starting in 1997.

Turbulent fluxes by "Conditional Eddy Sampling"

Science.gov (United States)

Siebicke, Lukas

2015-04-01

Turbulent flux measurements are key to understanding ecosystem scale energy and matter exchange, including atmospheric trace gases. While the eddy covariance approach has evolved as an invaluable tool to quantify fluxes of e.g. CO2 and H2O continuously, it is limited to very few atmospheric constituents for which sufficiently fast analyzers exist. High instrument cost, lack of field-readiness or high power consumption (e.g. many recent laser-based systems requiring strong vacuum) further impair application to other tracers. Alternative micrometeorological approaches such as conditional sampling might overcome major limitations. Although the idea of eddy accumulation has already been proposed by Desjardin in 1972 (Desjardin, 1977), at the time it could not be realized for trace gases. Major simplifications by Businger and Oncley (1990) lead to it's widespread application as 'Relaxed Eddy Accumulation' (REA). However, those simplifications (flux gradient similarity with constant flow rate sampling irrespective of vertical wind velocity and introduction of a deadband around zero vertical wind velocity) have degraded eddy accumulation to an indirect method, introducing issues of scalar similarity and often lack of suitable scalar flux proxies. Here we present a real implementation of a true eddy accumulation system according to the original concept. Key to our approach, which we call 'Conditional Eddy Sampling' (CES), is the mathematical formulation of conditional sampling in it's true form of a direct eddy flux measurement paired with a performant real implementation. Dedicated hardware controlled by near-real-time software allows full signal recovery at 10 or 20 Hz, very fast valve switching, instant vertical wind velocity proportional flow rate control, virtually no deadband and adaptive power management. Demonstrated system performance often exceeds requirements for flux measurements by orders of magnitude. The system's exceptionally low power consumption is ideal

Consistent regional fluxes of CH4 and CO2 inferred from GOSAT proxy XCH4 : XCO2 retrievals, 2010-2014

Science.gov (United States)

Feng, Liang; Palmer, Paul I.; Bösch, Hartmut; Parker, Robert J.; Webb, Alex J.; Correia, Caio S. C.; Deutscher, Nicholas M.; Domingues, Lucas G.; Feist, Dietrich G.; Gatti, Luciana V.; Gloor, Emanuel; Hase, Frank; Kivi, Rigel; Liu, Yi; Miller, John B.; Morino, Isamu; Sussmann, Ralf; Strong, Kimberly; Uchino, Osamu; Wang, Jing; Zahn, Andreas

2017-04-01

We use the GEOS-Chem global 3-D model of atmospheric chemistry and transport and an ensemble Kalman filter to simultaneously infer regional fluxes of methane (CH4) and carbon dioxide (CO2) directly from GOSAT retrievals of XCH4 : XCO2, using sparse ground-based CH4 and CO2 mole fraction data to anchor the ratio. This work builds on the previously reported theory that takes into account that (1) these ratios are less prone to systematic error than either the full-physics data products or the proxy CH4 data products; and (2) the resulting CH4 and CO2 fluxes are self-consistent. We show that a posteriori fluxes inferred from the GOSAT data generally outperform the fluxes inferred only from in situ data, as expected. GOSAT CH4 and CO2 fluxes are consistent with global growth rates for CO2 and CH4 reported by NOAA and have a range of independent data including new profile measurements (0-7 km) over the Amazon Basin that were collected specifically to help validate GOSAT over this geographical region. We find that large-scale multi-year annual a posteriori CO2 fluxes inferred from GOSAT data are similar to those inferred from the in situ surface data but with smaller uncertainties, particularly over the tropics. GOSAT data are consistent with smaller peak-to-peak seasonal amplitudes of CO2 than either the a priori or in situ inversion, particularly over the tropics and the southern extratropics. Over the northern extratropics, GOSAT data show larger uptake than the a priori but less than the in situ inversion, resulting in small net emissions over the year. We also find evidence that the carbon balance of tropical South America was perturbed following the droughts of 2010 and 2012 with net annual fluxes not returning to an approximate annual balance until 2013. In contrast, GOSAT data significantly changed the a priori spatial distribution of CH4 emission with a 40 % increase over tropical South America and tropical Asia and a smaller decrease over Eurasia and temperate

Modeling the impacts of temperature and precipitation changes on soil CO2 fluxes from a Switchgrass stand recently converted from cropland.

Science.gov (United States)

Lai, Liming; Kumar, Sandeep; Chintala, Rajesh; Owens, Vance N; Clay, David; Schumacher, Joseph; Nizami, Abdul-Sattar; Lee, Sang Soo; Rafique, Rashad

2016-05-01

Switchgrass (Panicum virgatum L.) is a perennial C4 grass native to North America and successfully adapted to diverse environmental conditions. It offers the potential to reduce soil surface carbon dioxide (CO2) fluxes and mitigate climate change. However, information on how these CO2 fluxes respond to changing climate is still lacking. In this study, CO2 fluxes were monitored continuously from 2011 through 2014 using high frequency measurements from Switchgrass land seeded in 2008 on an experimental site that has been previously used for soybean (Glycine max L.) in South Dakota, USA. DAYCENT, a process-based model, was used to simulate CO2 fluxes. An improved methodology CPTE [Combining Parameter estimation (PEST) with "Trial and Error" method] was used to calibrate DAYCENT. The calibrated DAYCENT model was used for simulating future CO2 emissions based on different climate change scenarios. This study showed that: (i) the measured soil CO2 fluxes from Switchgrass land were higher for 2012 which was a drought year, and these fluxes when simulated using DAYCENT for long-term (2015-2070) provided a pattern of polynomial curve; (ii) the simulated CO2 fluxes provided different patterns with temperature and precipitation changes in a long-term, (iii) the future CO2 fluxes from Switchgrass land under different changing climate scenarios were not significantly different, therefore, it can be concluded that Switchgrass grown for longer durations could reduce changes in CO2 fluxes from soil as a result of temperature and precipitation changes to some extent. Copyright © 2015. Published by Elsevier B.V.

Prediction of soil CO2 flux in sugarcane management systems using the Random Forest approach

Directory of Open Access Journals (Sweden)

Rose Luiza Moraes Tavares

Full Text Available ABSTRACT: The Random Forest algorithm is a data mining technique used for classifying attributes in order of importance to explain the variation in an attribute-target, as soil CO2 flux. This study aimed to identify prediction of soil CO2 flux variables in management systems of sugarcane through the machine-learning algorithm called Random Forest. Two different management areas of sugarcane in the state of São Paulo, Brazil, were selected: burned and green. In each area, we assembled a sampling grid with 81 georeferenced points to assess soil CO2 flux through automated portable soil gas chamber with measuring spectroscopy in the infrared during the dry season of 2011 and the rainy season of 2012. In addition, we sampled the soil to evaluate physical, chemical, and microbiological attributes. For data interpretation, we used the Random Forest algorithm, based on the combination of predicted decision trees (machine learning algorithms in which every tree depends on the values of a random vector sampled independently with the same distribution to all the trees of the forest. The results indicated that clay content in the soil was the most important attribute to explain the CO2 flux in the areas studied during the evaluated period. The use of the Random Forest algorithm originated a model with a good fit (R2 = 0.80 for predicted and observed values.

Searching Sinks and Sources: CO2 Fluxes Before and After Partial Deforestation of a Spruce Forest

Science.gov (United States)

Ney, P.; Graf, A.; Druee, C.; Esser, O.; Klosterhalfen, A.; Valler, V.; Pick, K.; Vereecken, H.

2017-12-01

Forest ecosystems in the northern mid-latitudes act as a sink for atmospheric carbon dioxide (CO2) and hence play an important role in the terrestrial carbon cycle. Disturbances of these landscapes may have a significant impact on their ecosystem carbon budget. We present seven years of eddy covariance (EC) measurements (September 2013 to September 2017) over a 70 year old spruce stock, including three years prior to and four years after partial deforestation. We analyzed the seasonal and inter-annual changes of carbon fluxes as affected mainly by the forest transition. The measurements were carried out in a small headwater catchment (38.5 ha) within the TERENO (TERrestrial Environmental Observatories) network in the Eifel National Park Germany (50°30'N, 06°19'E, 595-629 m a.s.l.). An EC system, mounted on the top of a 38 m high tower, continuously samples fluxes of momentum, sensible heat, latent heat and CO2. In August and September 2013, more than 20% of the catchment was deforested and planned for regeneration towards natural deciduous vegetation, and a second EC station (2.5 m height) was installed in the middle of this clearcut. Flux partitioning and gap filling methods were used to calculate full time series and annual carbon budgets of the measured net ecosystem exchange (NEE) and its components gross primary production (GPP) and total ecosystem respiration (Reco). Additionally, soil respiration was measured with manual chambers on a monthly to bi-monthly basis at 25 transect points in the forest and deforested area. Annual sums of NEE represent the forest as a carbon sink with small inter-annual variability. In contrast, the deforested area showed a clear trend. In the first year after partial deforestation, regrowth on the deforested area consisted mainly of grasses and red foxglove (Digitalis purpurea L.), while since the second year also growth of mountain ash (Sorbus aucuparia L.) and broom (Cytisus scoparius L.) increased. The regrowth of biomass is

[Temperature sensitivity of CO2 fluxes from rhizosphere soil mineralization and root decomposition in Pinus massoniana and Castanopsis sclerophylla forests].

Science.gov (United States)

Liu, Yu; Hu, Xiao-Fei; Chen, Fu-Sheng; Yuan, Ping-Cheng

2013-06-01

Rhizospheric and non-rhizospheric soils and the absorption, transition, and storage roots were sampled from the mid-subtropical Pinus massoniana and Castanopsis sclerophylla forests to study the CO2 fluxes from soil mineralization and root decomposition in the forests. The samples were incubated in closed jars at 15 degrees C, 25 degrees C, 35 degrees C, and 45 degrees C, respectively, and alkali absorption method was applied to measure the CO2 fluxes during 53 days incubation. For the two forests, the rhizospheric effect (ratio of rhizospheric to non-rhizospheric soil) on the CO2 flux from soil mineralization across all incubation temperature ranged from 1.12 to 3.09, with a decreasing trend along incubation days. There was no significant difference in the CO2 flux from soil mineralization between the two forests at 15 degrees C, but the CO2 flux was significantly higher in P. massoniana forest than in C. sclerophylla forest at 25 degrees C and 35 degrees C, and in an opposite pattern at 45 degrees C. At all incubation temperature, the CO2 release from the absorption root decomposition was higher than that from the transition and storage roots decomposition, and was smaller in P. massoniana than in C. sclerophylla forest for all the root functional types. The Q10 values of the CO2 fluxes from the two forests were higher for soils (1.21-1.83) than for roots (0.96-1.36). No significant differences were observed in the Q10 values of the CO2 flux from soil mineralization between the two forests, but the Q10 value of the CO2 flux from root decomposition was significantly higher in P. massoniana than in C. sclerophylla forest. It was suggested that the increment of CO2 flux from soil mineralization under global warming was far higher than that from root decomposition, and for P. massoniana than for C. sclerophylla forest. In subtropics of China, the adaptability of zonal climax community to global warming would be stronger than that of pioneer community.

Relative humidity effects on water vapour fluxes measured with closed-path eddy-covariance systems with short sampling lines

DEFF Research Database (Denmark)

Fratini, Gerardo; Ibrom, Andreas; Arriga, Nicola

2012-01-01

It has been formerly recognised that increasing relative humidity in the sampling line of closed-path eddy-covariance systems leads to increasing attenuation of water vapour turbulent fluctuations, resulting in strong latent heat flux losses. This occurrence has been analyzed for very long (50 m...... from eddy-covariance systems featuring short (4 m) and very short (1 m) sampling lines running at the same clover field and show that relative humidity effects persist also for these setups, and should not be neglected. Starting from the work of Ibrom and co-workers, we propose a mixed method...... and correction method proposed here is deemed applicable to closed-path systems featuring a broad range of sampling lines, and indeed applicable also to passive gases as a special case. The methods described in this paper are incorporated, as processing options, in the free and open-source eddy...

Interannual variability in CO2 and CH4 exchange in a brackish tidal marsh in Northern California

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Knox, S. H.; Windham-Myers, L.; Anderson, F. E.; Bergamaschi, B. A.

2017-12-01

Carbon (C) cycling in coastal wetlands is difficult to measure and model due to extremely dynamic atmospheric and hydrologic fluxes, as well as sensitivities to dynamic land- and ocean-based drivers. To date, few studies have begun continuous measurements of net ecosystem CO2 exchange (NEE) in these systems, and as such our understanding of the key drivers of NEE in coastal wetlands remain poorly understood. Recent eddy covariance measurements of NEE in these environments show considerable variability both within and across sites, with daily CO2 uptake and annual net CO2 budgets varying by nearly an order of magnitude between years and across locations. Furthermore, measurements of CH4 fluxes in these systems are even more limited, despite the potential for CH4 emissions from brackish and freshwater coastal wetlands. Here we present 3 years of near-continuous eddy covariance measurements of CO2 and CH4 fluxes from a brackish tidal marsh in Northern California and explore the drivers of interannual variability in CO2 and CH4 exchange. CO2 fluxes showed significant interannual variability; net CO2 uptake was near-zero in 2014 (6 ± 26 g C-CO2 m-2 yr-1), while much greater uptake was observed in 2015 and 2016 (209 ± 27 g C- CO2 m-2 yr-1 and 243 ± 26 g C-CO2 m-2 yr-1, respectively). Conversely, annual CH4 emissions were small and consistent across years, with the wetland emitting on average 1 ± 0.1 g C-CH4 m-2 yr-1. With respect to the net atmospheric GHG budget (assuming a sustained global warming potential (SGWP) of 45, expressed in units of CO2 equivalents), the wetland was near neutral in 2014, but a net GHG sink of 706 ± 105 g CO2 eq m-2 yr-1 and 836 ± 83 g CO2 eq m-2 yr-1 in 2015 and 2016, respectively. The large interannual variability in CO2 exchange was driven by notable year-to-year differences in temperature and precipitation as California experienced a severe drought and record high temperatures from 2012 to 2015. The large interannual variability in

Comparison of Sensible Heat Flux from Eddy Covariance and Scintillometer over different land surface conditions

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Zeweldi, D. A.; Gebremichael, M.; Summis, T.; Wang, J.; Miller, D.

2008-12-01

The large source of uncertainty in satellite-based evapotranspiration algorithm results from the estimation of sensible heat flux H. Traditionally eddy covariance sensors, and recently large-aperture scintillometers, have been used as ground truth to evaluate satellite-based H estimates. The two methods rely on different physical measurement principles, and represent different foot print sizes. In New Mexico, we conducted a field campaign during summer 2008 to compare H estimates obtained from the eddy covariance and scintillometer methods. During this field campaign, we installed sonic anemometers; one propeller eddy covariance (OPEC) equipped with net radiometer and soil heat flux sensors; large aperture scintillometer (LAS); and weather station consisting of wind speed, direction and radiation sensors over three different experimental areas consisting of different roughness conditions (desert, irrigated area and lake). Our results show the similarities and differences in H estimates obtained from these various methods over the different land surface conditions. Further, our results show that the H estimates obtained from the LAS agree with those obtained from the eddy covariance method when high frequency thermocouple temperature, instead of the typical weather station temperature measurements, is used in the LAS analysis.

Fluxes of CH4 and N2O in aspen stands grown under ambient and twice-ambient CO2

DEFF Research Database (Denmark)

Ambus, P.; Robertson, G.P.

1999-01-01

Elevated atmospheric CO2 has the potential to change below-ground nutrient cycling and thereby alter the soil-atmosphere exchange of biogenic trace gases. We measured fluxes of CH4 and N2O in trembling aspen (Populus tremuloides Michx.) stands grown in open-top chambers under ambient and twice......-ambient CO2 concentrations crossed with `high' and low soil-N conditions. Flux measurements with small static chambers indicated net CH4 oxidation in the open-top chambers. Across dates, CH4 oxidation activity was significantly (P CO2 (8.7 mu g CH4-C m(-2) h(-1)) than...... with elevated CO2 (6.5 mu g CH4-C m(-2) h(-1)) in the low N soil. Likewise, across dates and soil N treatments CH4 was oxidized more rapidly (P CO2 (9.5 mu g CH4-C m(-2) h(-1)) than in chambers with elevated CO2 (8.8 mu g CH4-C m(-2) h(-1)). Methane oxidation in soils incubated...

Effect of recent observations on Asian CO2 flux estimates by transport model inversions

International Nuclear Information System (INIS)

Maksyutov, Shamil; Patra, Prabir K.; Machida, Toshinobu; Mukai, Hitoshi; Nakazawa, Takakiyo; Inoue, Gen

2003-01-01

We use an inverse model to evaluate the effects of the recent CO 2 observations over Asia on estimates of regional CO 2 sources and sinks. Global CO 2 flux distribution is evaluated using several atmospheric transport models, atmospheric CO 2 observations and a 'time-independent' inversion procedure adopted in the basic synthesis inversion by the Transcom-3 inverse model intercomparison project. In our analysis we include airborne and tower observations in Siberia, continuous monitoring and airborne observations over Japan, and airborne monitoring on regular flights on Tokyo-Sydney route. The inclusion of the new data reduces the uncertainty of the estimated regional CO 2 fluxes for Boreal Asia (Siberia), Temperate Asia and South-East Asia. The largest effect is observed for the emission/sink estimate for the Boreal Asia region, where introducing the observations in Siberia reduces the source uncertainty by almost half. It also produces an uncertainty reduction for Boreal North America. Addition of the Siberian airborne observations leads to projecting extra sinks in Boreal Asia of 0.2 Pg C/yr, and a smaller change for Europe. The Tokyo-Sydney observations reduce and constrain the Southeast Asian source

An Inversion Analysis of Recent Variability in Natural CO2 Fluxes Using GOSAT and In Situ Observations

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Wang, James S.; Kawa, S. Randolph; Collatz, G. James; Baker, David F.; Ott, Lesley

2015-01-01

About one-half of the global CO2 emissions from fossil fuel combustion and deforestation accumulates in the atmosphere, where it contributes to global warming. The rest is taken up by vegetation and the ocean. The precise contribution of the two sinks, and their location and year-to-year variability are, however, not well understood. We use two different approaches, batch Bayesian synthesis inversion and variational data assimilation, to deduce the global spatiotemporal distributions of CO2 fluxes during 2009-2010. One of our objectives is to assess different sources of uncertainties in inferred fluxes, including uncertainties in prior flux estimates and observations, and differences in inversion techniques. For prior constraints, we utilize fluxes and uncertainties from the CASA-GFED model of the terrestrial biosphere and biomass burning driven by satellite observations and interannually varying meteorology. We also use measurement-based ocean flux estimates and two sets of fixed fossil CO2 emissions. Here, our inversions incorporate column CO2 measurements from the GOSAT satellite (ACOS retrieval, filtered and bias-corrected) and in situ observations (individual flask and afternoon-average continuous observations) to estimate fluxes in 108 regions over 8-day intervals for the batch inversion and at 3 x 3.75 weekly for the variational system. Relationships between fluxes and atmospheric concentrations are derived consistently for the two inversion systems using the PCTM atmospheric transport model driven by meteorology from the MERRA reanalysis. We compare the posterior fluxes and uncertainties derived using different data sets and the two inversion approaches, and evaluate the posterior atmospheric concentrations against independent data including aircraft measurements. The optimized fluxes generally resemble those from other studies. For example, the results indicate that the terrestrial biosphere is a net CO2 sink, and a GOSAT-only inversion suggests a shift in

Evaluating the Capacity of Global CO2 Flux and Atmospheric Transport Models to Incorporate New Satellite Observations

Science.gov (United States)

Kawa, S. R.; Collatz, G. J.; Erickson, D. J.; Denning, A. S.; Wofsy, S. C.; Andrews, A. E.

2007-01-01

As we enter the new era of satellite remote sensing for CO2 and other carbon cyclerelated quantities, advanced modeling and analysis capabilities are required to fully capitalize on the new observations. Model estimates of CO2 surface flux and atmospheric transport are required for initial constraints on inverse analyses, to connect atmospheric observations to the location of surface sources and sinks, and ultimately for future projections of carbon-climate interactions. For application to current, planned, and future remotely sensed CO2 data, it is desirable that these models are accurate and unbiased at time scales from less than daily to multi-annual and at spatial scales from several kilometers or finer to global. Here we focus on simulated CO2 fluxes from terrestrial vegetation and atmospheric transport mutually constrained by analyzed meteorological fields from the Goddard Modeling and Assimilation Office for the period 1998 through 2006. Use of assimilated meteorological data enables direct model comparison to observations across a wide range of scales of variability. The biospheric fluxes are produced by the CASA model at lxi degrees on a monthly mean basis, modulated hourly with analyzed temperature and sunlight. Both physiological and biomass burning fluxes are derived using satellite observations of vegetation, burned area (as in GFED-2), and analyzed meteorology. For the purposes of comparison to CO2 data, fossil fuel and ocean fluxes are also included in the transport simulations. In this presentation we evaluate the model's ability to simulate CO2 flux and mixing ratio variability in comparison to in situ observations at sites in Northern mid latitudes and the continental tropics. The influence of key process representations is inferred. We find that the model can resolve much of the hourly to synoptic variability in the observations, although there are limits imposed by vertical resolution of boundary layer processes. The seasonal cycle and its

Carbon dioxide fluxes from an urban area in Beijing

Science.gov (United States)

Song, Tao; Wang, Yuesi

2012-03-01

A better understanding of urban carbon dioxide (CO 2) emissions is important for quantifying urban contributions to the global carbon budget. From January to December 2008, CO 2 fluxes were measured, by eddy covariance at 47 m above ground on a meteorological tower in a high-density residential area in Beijing. The results showed that the urban surface was a net source of CO 2 in the atmosphere. Diurnal flux patterns were similar to those previously observed in other cities and were largely influenced by traffic volume. Carbon uptake by both urban vegetation during the growing season and the reduction of fuel consumption for domestic heating resulted in less-positive daily fluxes in the summer. The average daily flux measured in the summer was 0.48 mg m - 2 s - 1 , which was 82%, 35% and 36% lower than those in the winter, spring and autumn, respectively. The reduction of vehicles on the road during the 29th Olympic and Paralympic Games had a significant impact on CO 2 flux. The flux of 0.40 mg m - 2 s - 1 for September 2008 was approximately 0.17 mg m - 2 s - 1 lower than the flux for September 2007. Annual CO 2 emissions from the study site were estimated at 20.6 kg CO 2 m - 2 y - 1 , considerably higher than yearly emissions obtained from other urban and suburban landscapes.

Field intercomparison of four methane gas analyzers suitable for eddy covariance flux measurements

Science.gov (United States)

Peltola, O.; Mammarella, I.; Haapanala, S.; Burba, G.; Vesala, T.

2013-06-01

Performances of four methane gas analyzers suitable for eddy covariance measurements are assessed. The assessment and comparison was performed by analyzing eddy covariance data obtained during summer 2010 (1 April to 26 October) at a pristine fen, Siikaneva, Southern Finland. High methane fluxes with pronounced seasonality have been measured at this fen. The four participating methane gas analyzers are commercially available closed-path units TGA-100A (Campbell Scientific Inc., USA), RMT-200 (Los Gatos Research, USA), G1301-f (Picarro Inc., USA) and an early prototype open-path unit Prototype-7700 (LI-COR Biosciences, USA). The RMT-200 functioned most reliably throughout the measurement campaign, during low and high flux periods. Methane fluxes from RMT-200 and G1301-f had the smallest random errors and the fluxes agree remarkably well throughout the measurement campaign. Cospectra and power spectra calculated from RMT-200 and G1301-f data agree well with corresponding temperature spectra during a high flux period. None of the gas analyzers showed statistically significant diurnal variation for methane flux. Prototype-7700 functioned only for a short period of time, over one month, in the beginning of the measurement campaign during low flux period, and thus, its overall accuracy and season-long performance were not assessed. The open-path gas analyzer is a practical choice for measurement sites in remote locations due to its low power demand, whereas for G1301-f methane measurements interference from water vapor is straightforward to correct since the instrument measures both gases simultaneously. In any case, if only the performance in this intercomparison is considered, RMT-200 performed the best and is the recommended choice if a new fast response methane gas analyzer is needed.

SOIL 222Rn CONCENTRATION, CO2 AND CH4 FLUX MEASUREMENTS AROUND THE JWALAMUKHI AREA OF NORTH-WEST HIMALAYAS, INDIA.

Science.gov (United States)

Kumar, Arvind; Walia, Vivek; Yang, Tsanyao Frank; Fu, Ching-Chou; Singh, Surinder; Bajwa, Bikramjit Singh; Arora, Vishal

2016-10-01

Soil 222 Rn concentration, CO 2 and CH 4 flux measurements were conducted around the Jwalamukhi area of North-West Himalayas, India. During this study, around 37 soil gas points and flux measurements were taken with the aim to assure the suitability of this method in the study of fault zones. For this purpose, RAD 7 (Durridge, USA) was used to monitor radon concentrations, whereas portable diffuse flux meter (West Systems, Italy) was used for the CO 2 and CH 4 flux measurements. The recorded radon concentration varies from 6.1 to 34.5 kBq m -3 with an average value of 16.5 kBq m -3 The anomalous value of radon concentrations was recorded between Jwalamukhi thrust and Barsar thrust. The recorded average of CO 2 and CH 4 flux were 11.8 and 2.7 g m -2 day -1 , respectively. The good correlation between anomalous CO 2 flux and radon concentrations has been observed along the fault zone in the study area, suggesting that radon migration is dependent on CO 2 . © The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Air–Sea CO2 Gas Transfer Velocity in a Shallow Estuary

DEFF Research Database (Denmark)

Mørk, Eva Thorborg; Sørensen, Lise Lotte; Jensen, Bjarne

2014-01-01

The air–sea transfer velocity of CO2(kCO2) was investigated in a shallow estuary in March to July 2012, using eddy-covariance measurements of CO2 fluxes and measured air–sea CO2 partial-pressure differences. A data evaluation method that eliminates data by nine rejection criteria in order......, the transfer velocity in the shallow water estuary was lower than in other coastal waters, possibly a symptom of low tidal amplitude leading to low intensity water turbulence. High transfer velocities were recorded above wind speeds of 5 m s−1 , believed to be caused by early-breaking waves and the large fetch...... (6.5 km) of the estuary. These findings indicate that turbulence in both air and water influences the transfer velocity....

Temporal and spatial variations of soil CO2, CH4 and N2O fluxes at three differently managed grasslands

Directory of Open Access Journals (Sweden)

D. Imer

2013-09-01

Full Text Available A profound understanding of temporal and spatial variabilities of soil carbon dioxide (CO2, methane (CH4 and nitrous oxide (N2O fluxes between terrestrial ecosystems and the atmosphere is needed to reliably quantify these fluxes and to develop future mitigation strategies. For managed grassland ecosystems, temporal and spatial variabilities of these three soil greenhouse gas (GHG fluxes occur due to changes in environmental drivers as well as fertilizer applications, harvests and grazing. To assess how such changes affect soil GHG fluxes at Swiss grassland sites, we studied three sites along an altitudinal gradient that corresponds to a management gradient: from 400 m a.s.l. (intensively managed to 1000 m a.s.l. (moderately intensive managed to 2000 m a.s.l. (extensively managed. The alpine grassland was included to study both effects of extensive management on CH4 and N2O fluxes and the different climate regime occurring at this altitude. Temporal and spatial variabilities of soil GHG fluxes and environmental drivers on various timescales were determined along transects of 16 static soil chambers at each site. All three grasslands were N2O sources, with mean annual soil fluxes ranging from 0.15 to 1.28 nmol m−2 s−1. Contrastingly, all sites were weak CH4 sinks, with soil uptake rates ranging from −0.56 to −0.15 nmol m−2 s−1. Mean annual soil and plant respiration losses of CO2, measured with opaque chambers, ranged from 5.2 to 6.5 μmol m−2 s−1. While the environmental drivers and their respective explanatory power for soil N2O emissions differed considerably among the three grasslands (adjusted r2 ranging from 0.19 to 0.42, CH4 and CO2 soil fluxes were much better constrained (adjusted r2 ranging from 0.46 to 0.80 by soil water content and air temperature, respectively. Throughout the year, spatial heterogeneity was particularly high for soil N2O and CH4 fluxes. We found permanent hot spots for soil N2O emissions as well as

Regional CO2 and latent heat surface fluxes in the Southern Great Plains: Measurements, modeling, and scaling

Energy Technology Data Exchange (ETDEWEB)

Riley, W. J.; Biraud, S.C.; Torn, M.S.; Fischer, M.L.; Billesbach, D.P.; Berry, J.A.

2009-08-15

Characterizing net ecosystem exchanges (NEE) of CO{sub 2} and sensible and latent heat fluxes in heterogeneous landscapes is difficult, yet critical given expected changes in climate and land use. We report here a measurement and modeling study designed to improve our understanding of surface to atmosphere gas exchanges under very heterogeneous land cover in the mostly agricultural U.S. Southern Great Plains (SGP). We combined three years of site-level, eddy covariance measurements in several of the dominant land cover types with regional-scale climate data from the distributed Mesonet stations and Next Generation Weather Radar precipitation measurements to calibrate a land surface model of trace gas and energy exchanges (isotope-enabled land surface model (ISOLSM)). Yearly variations in vegetation cover distributions were estimated from Moderate Resolution Imaging Spectroradiometer normalized difference vegetation index and compared to regional and subregional vegetation cover type estimates from the U.S. Department of Agriculture census. We first applied ISOLSM at a 250 m spatial scale to account for vegetation cover type and leaf area variations that occur on hundred meter scales. Because of computational constraints, we developed a subsampling scheme within 10 km 'macrocells' to perform these high-resolution simulations. We estimate that the Atmospheric Radiation Measurement Climate Research Facility SGP region net CO{sub 2} exchange with the local atmosphere was -240, -340, and -270 gC m{sup -2} yr{sup -1} (positive toward the atmosphere) in 2003, 2004, and 2005, respectively, with large seasonal variations. We also performed simulations using two scaling approaches at resolutions of 10, 30, 60, and 90 km. The scaling approach applied in current land surface models led to regional NEE biases of up to 50 and 20% in weekly and annual estimates, respectively. An important factor in causing these biases was the complex leaf area index (LAI) distribution

Forest soil CO2 fluxes as a function of understory removal and N-fixing species addition.

Science.gov (United States)

Li, Haifang; Fu, Shenglei; Zhao, Hongting; Xia, Hanping

2011-01-01

We report on the effects of forest management practices of understory removal and N-fixing species (Cassia alata) addition on soil CO2 fluxes in an Eucalyptus urophylla plantation (EUp), Acacia crassicarpa plantation (ACp), 10-species-mixed plantation (Tp), and 30-species-mixed plantation (THp) using the static chamber method in southern China. Four forest management treatments, including (1) understory removal (UR); (2) C. alata addition (CA); (3) understory removal and replacement with C. alata (UR+CA); and (4) control without any disturbances (CK), were applied in the above four forest plantations with three replications for each treatment. The results showed that soil CO2 fluxes rates remained at a high level during the rainy season (from April to September), followed by a rapid decrease after October reaching a minimum in February. Soil CO2 fluxes were significantly higher (P plantations under various management practices.

ORCHIDEE-PEAT (revision 4596), a model for northern peatland CO2, water, and energy fluxes on daily to annual scales

Science.gov (United States)

Qiu, Chunjing; Zhu, Dan; Ciais, Philippe; Guenet, Bertrand; Krinner, Gerhard; Peng, Shushi; Aurela, Mika; Bernhofer, Christian; Brümmer, Christian; Bret-Harte, Syndonia; Chu, Housen; Chen, Jiquan; Desai, Ankur R.; Dušek, Jiří; Euskirchen, Eugénie S.; Fortuniak, Krzysztof; Flanagan, Lawrence B.; Friborg, Thomas; Grygoruk, Mateusz; Gogo, Sébastien; Grünwald, Thomas; Hansen, Birger U.; Holl, David; Humphreys, Elyn; Hurkuck, Miriam; Kiely, Gerard; Klatt, Janina; Kutzbach, Lars; Largeron, Chloé; Laggoun-Défarge, Fatima; Lund, Magnus; Lafleur, Peter M.; Li, Xuefei; Mammarella, Ivan; Merbold, Lutz; Nilsson, Mats B.; Olejnik, Janusz; Ottosson-Löfvenius, Mikaell; Oechel, Walter; Parmentier, Frans-Jan W.; Peichl, Matthias; Pirk, Norbert; Peltola, Olli; Pawlak, Włodzimierz; Rasse, Daniel; Rinne, Janne; Shaver, Gaius; Schmid, Hans Peter; Sottocornola, Matteo; Steinbrecher, Rainer; Sachs, Torsten; Urbaniak, Marek; Zona, Donatella; Ziemblinska, Klaudia

2018-02-01

Peatlands store substantial amounts of carbon and are vulnerable to climate change. We present a modified version of the Organising Carbon and Hydrology In Dynamic Ecosystems (ORCHIDEE) land surface model for simulating the hydrology, surface energy, and CO2 fluxes of peatlands on daily to annual timescales. The model includes a separate soil tile in each 0.5° grid cell, defined from a global peatland map and identified with peat-specific soil hydraulic properties. Runoff from non-peat vegetation within a grid cell containing a fraction of peat is routed to this peat soil tile, which maintains shallow water tables. The water table position separates oxic from anoxic decomposition. The model was evaluated against eddy-covariance (EC) observations from 30 northern peatland sites, with the maximum rate of carboxylation (Vcmax) being optimized at each site. Regarding short-term day-to-day variations, the model performance was good for gross primary production (GPP) (r2 = 0.76; Nash-Sutcliffe modeling efficiency, MEF = 0.76) and ecosystem respiration (ER, r2 = 0.78, MEF = 0.75), with lesser accuracy for latent heat fluxes (LE, r2 = 0.42, MEF = 0.14) and and net ecosystem CO2 exchange (NEE, r2 = 0.38, MEF = 0.26). Seasonal variations in GPP, ER, NEE, and energy fluxes on monthly scales showed moderate to high r2 values (0.57-0.86). For spatial across-site gradients of annual mean GPP, ER, NEE, and LE, r2 values of 0.93, 0.89, 0.27, and 0.71 were achieved, respectively. Water table (WT) variation was not well predicted (r2 < 0.1), likely due to the uncertain water input to the peat from surrounding areas. However, the poor performance of WT simulation did not greatly affect predictions of ER and NEE. We found a significant relationship between optimized Vcmax and latitude (temperature), which better reflects the spatial gradients of annual NEE than using an average Vcmax value.

Tactile communication using a CO(2) flux stimulation for blind or deafblind people.

Science.gov (United States)

da Cunha, Jose Carlos; Bordignon, Luiz Alberto; Nohama, Percy

2010-01-01

This paper describes a tactile stimulation system for producing nonvisual image patterns to blind or deafblind people. The stimulator yields a CO(2) pulsatile flux directed to the user's skin throughout a needle that is coupled to a 2-D tactile plotter. The fluxtactile plotter operates with two step motor mounted on a wood structure, controlled by a program developed to produce alphanumerical characters and geometric figures of different size and speed, which will be used to investigate the psychophysical properties of this kind of tactile communication. CO(2) is provided by a cylinder that delivers a stable flux, which is converted to a pulsatile mode through a high frequency solenoid valve that can chop it up to 1 kHz. Also, system temperature is controlled by a Peltier based device. Tests on the prototype indicate that the system is a valuable tool to investigate the psychophysical properties of the skin in response to stimulation by CO(2) jet, allowing a quantitative and qualitative analysis as a function of stimulation parameters. With the system developed, it was possible to plot the geometric figures proposed: triangles, rectangles and octagons, in different sizes and speeds, and verify the control of the frequency of CO(2) jet stimuli.

UU* filtering of nighttime net ecosystem CO2 exchange flux over forest canopy under strong wind in wintertime

Institute of Scientific and Technical Information of China (English)

ZHANG; Junhui

2005-01-01

［1］Aubinet, M., Heinesch, B., Longdoz, B., Estimation of the carbon sequestration by a heterogeneous forest: night flux corrections,heterogeneity of the site and inter-annual variability, Global Change Biology, 2002, 8:1053-1071.［2］Charlotte, L.R., Nigel, T.R., Seasonal contribution of CO2 fluxes in the annual C budget of a northern bog, Global Biogeochemical Cycles, 2003, 171029, doi: 10.1029/20029B001889.［3］Baldocchi, D.D., Hicks, B.B., Meyers, T. P., Measuring biosphere-atmosphere exchanges of biologically related gases with micrometeorological methods, Ecology, 1988, 69:1331-1340.［4］Baldocchi, D.D., Assessing ecosystem carbon balance: problems and prospects of the eddy covariance technique, Global change biology, 2003, 9: 478-492.［5］Canadell, J. G., Mooney, H. A., Baldocchi, D. D. et al., Carbon metabolism of the terrestrial biosphere: A multi technique approach for improved understanding, Ecosystems, 2000, 3:115-130.［6］Schmid, H. P., Footprint modeling for vegetation atmosphere exchange studies: a review and perspective, Agricultural and Forest Meteorology, 2002, 113: 159-183.［7］Wofsy, S. C., Goulden, M. L., Munger, J. W. et al., Net exchange on CO2 in a mid-latitude forest, Science, 1993, 260: 1314-1317.［8］Massman, W. J., Lee, X. H., Eddy covariance flux corrections and uncertainties in long-term studies of carbon and energy exchanges,Agricultural and Forest Meteorology, 2002, 113: 121-144.［9］Baldocchi, D. D., Finnigan, J., Wilson, K. et al., On measuring net ecosystem carbon exchange over tall vegetation on complex terrain, Boundary-Layer Meteorology, 2000, 96: 257-291.［10］Anthoni, P. M., Unsworth, M. H., Law, B. E. et al., Seasonal differences in carbon and water vapor exchange in young and old-growth ponderosa pine ecosystems, Agricultural and Forest Meteorology, 2002, 111: 203-222.［11］Paw U, K. T., Baldocchi, D. D., Meyers, T. P. et al., Correction of eddy-covariance measurements incorporating both advective

Effects of climate factors and vegetation on the CO2 fluxes and δ13C from re-established grassland

Science.gov (United States)

Bezyk, Yaroslav; Dorodnikov, Maxim; Sówka, Izabela

2017-11-01

The relationship between stable carbon isotope composition (δ13C -CO2) of soil CO2 flux, vegetation cover and weather conditions was investigated in a short-term campaign at a temperate re-established grassland in Germany. During August-September 2016, we measured surface CO2 flux with a closed-chamber method at high and low soil moisture content (`wet', `dry'), with and without above ground vegetation (`planted', `clear-cut') and estimated the effects of treatments on respective δ13C -CO2 values. The concentration and stable carbon isotope composition of CO2 were determined using the gas chromatography and mass spectrometry analyses. The δ13C -CO2 of the soil fluxes decreased over sampling time for the `dry-warm' conditions and canopy manipulation. The ecosystem-derived δ13C -CO2 values (corrected for the atmospheric δ13C -CO2) which included predominately soil-and rhizosphere respiration were -26.2 ± 0.8‰ for the `dry-warm' conditions and decreased down to -28.1 ± 1.4‰ over a period of 28 days from late August to the end of September. The decrease coincided with the lowering of CO2 flux and could be attributed to changes in plant physiological processes at the end of the vegetation season. Though the removal of shoots did not significantly affect the δ13C -CO2 values as compared with the control, the pattern of further δ13C -CO2 decrease (down to -28.8 ± 0.8‰) supported the role of living vegetation in a contribution of 13C-enriched CO2 to the ecosystem respiration.

Momentum, sensible heat and CO2 correlation coefficient variability: what can we learn from 20 years of continuous eddy covariance measurements?

Science.gov (United States)

Hurdebise, Quentin; Heinesch, Bernard; De Ligne, Anne; Vincke, Caroline; Aubinet, Marc

2017-04-01

Long-term data series of carbon dioxide and other gas exchanges between terrestrial ecosystems and atmosphere become more and more numerous. Long-term analyses of such exchanges require a good understanding of measurement conditions during the investigated period. Independently of climate drivers, measurements may indeed be influenced by measurement conditions themselves subjected to long-term variability due to vegetation growth or set-up changes. The present research refers to the Vielsalm Terrestrial Observatory (VTO) an ICOS candidate site located in a mixed forest (beech, silver fir, Douglas fir, Norway spruce) in the Belgian Ardenne. Fluxes of momentum, carbon dioxide and sensible heat have been continuously measured there by eddy covariance for more than 20 years. During this period, changes in canopy height and measurement height occurred. The correlation coefficients (for momemtum, sensible heat and CO2) and the normalized standard deviations measured for the past 20 years at the Vielsalm Terrestrial Observatory (VTO) were analysed in order to define how the fluxes, independently of climate conditions, were affected by the surrounding environment evolution, including tree growth, forest thinning and tower height change. A relationship between canopy aerodynamic distance and the momentum correlation coefficient was found which is characteristic of the roughness sublayer, and suggests that momentum transport processes were affected by z-d. In contrast, no relationship was found for sensible heat and CO2 correlation coefficients, suggesting that the z-d variability observed did not affect their turbulent transport. There were strong differences in these coefficients, however, between two wind sectors, characterized by contrasted stands (height differences, homogeneity) and different hypotheses were raised to explain it. This study highlighted the importance of taking the surrounding environment variability into account in order to ensure the spatio

Summer fluxes of atmospheric greenhouse gases N{sub 2}O, CH{sub 4} and CO{sub 2} from mangrove soil in South China

Energy Technology Data Exchange (ETDEWEB)

Chen, G.C. [Department of Biology and Chemistry, City University of Hong Kong, Hong Kong SAR (China); Tam, N.F.Y., E-mail: bhntam@cityu.edu.hk [Department of Biology and Chemistry, City University of Hong Kong, Hong Kong SAR (China); Ye, Y. [State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, Fujian (China)

2010-06-01

The atmospheric fluxes of N{sub 2}O, CH{sub 4} and CO{sub 2} from the soil in four mangrove swamps in Shenzhen and Hong Kong, South China were investigated in the summer of 2008. The fluxes ranged from 0.14 to 23.83 {mu}mol m{sup -2} h{sup -1}, 11.9 to 5168.6 {mu}mol m{sup -2} h{sup -1} and 0.69 to 20.56 mmol m{sup -2} h{sup -1} for N{sub 2}O, CH{sub 4} and CO{sub 2}, respectively. Futian mangrove swamp in Shenzhen had the highest greenhouse gas fluxes, followed by Mai Po mangrove in Hong Kong. Sha Kong Tsuen and Yung Shue O mangroves in Hong Kong had similar, low fluxes. The differences in both N{sub 2}O and CH{sub 4} fluxes among different tidal positions, the landward, seaward and bare mudflat, in each swamp were insignificant. The N{sub 2}O and CO{sub 2} fluxes were positively correlated with the soil organic carbon, total nitrogen, total phosphate, total iron and NH{sub 4}{sup +}-N contents, as well as the soil porosity. However, only soil NH{sub 4}{sup +}-N concentration had significant effects on CH{sub 4} fluxes.

Responses of CO2 Fluxes to Arctic Browning Events in a Range of High Latitude, Shrub-Dominated Ecosystems

Science.gov (United States)

Phoenix, G. K.; Treharne, R.; Emberson, L.; Tømmervik, H. A.; Bjerke, J. W.

2017-12-01

Climatic and biotic extreme events can result in considerable damage to arctic vegetation, often at landscape and larger scale. These acute events therefore contribute to the browning observed in some arctic regions. It is of considerable concern, therefore, that such extreme events are increasing in frequency as part of climate change. However, despite the increasing importance of browning events, and the considerable impact they can have on ecosystems, to date there is little understanding of their impacts on ecosystem carbon fluxes. To address this, the impacts of a number of different, commonly occurring, extreme events and their subsequent browning (vegetation damage) on key ecosystem CO2 fluxes were assessed during the growing season at a range of event damaged sites of shrub dominated vegetation. Sites were located from the boreal to High Arctic (64˚N-79˚N) and had been previously been damaged by events of frost-drought, extreme winter warming, ground icing and caterpillar (Epirrita autumnata) outbreaks. Plot-level CO2 fluxes of Ecosystem Exchange (NEE), Gross Primary Productivity (GPP) and Ecosystem Respiration (Reco) were assessed using vegetation chambers. At a sub-set of sites, NDVI (greenness) in flux plots was also assessed by hand-held proximal sensor, allowing the relationship between NDVI of damage plots to CO2 flux to be calculated. Despite the contrasting sites and drivers, damage had consistent, major impacts on all fluxes. All sites showed reductions in GPP and NEE with increasing damage, despite efflux from Reco also declining with damage. When scaled to site-level, reductions of up to 81% of NEE, 51% of GPP and 37% of Reco were observed. In the plot-level NDVI-flux relationship, NDVI was shown to explain up to 91% of variation in GPP, and therefore supports the use of NDVI for estimating changes in ecosystem CO2 flux at larger scales in regions where browning has been driven by extreme events. This work is the first attempt to quantify the

Eddy covariance VOC emission and deposition fluxes above grassland using PTR-TOF

Directory of Open Access Journals (Sweden)

T. M. Ruuskanen

2011-01-01

Full Text Available Eddy covariance (EC is the preferable technique for flux measurements since it is the only direct flux determination method. It requires a continuum of high time resolution measurements (e.g. 5–20 Hz. For volatile organic compounds (VOC soft ionization via proton transfer reaction has proven to be a quantitative method for real time mass spectrometry; here we use a proton transfer reaction time of flight mass spectrometer (PTR-TOF for 10 Hz EC measurements of full mass spectra up to m/z 315. The mass resolution of the PTR-TOF enabled the identification of chemical formulas and separation of oxygenated and hydrocarbon species exhibiting the same nominal mass. We determined 481 ion mass peaks from ambient air concentration above a managed, temperate mountain grassland in Neustift, Stubai Valley, Austria. During harvesting we found significant fluxes of 18 compounds distributed over 43 ions, including protonated parent compounds, as well as their isotopes and fragments and VOC-H⁺ – water clusters. The dominant BVOC fluxes were methanol, acetaldehyde, ethanol, hexenal and other C₆ leaf wound compounds, acetone, acetic acid, monoterpenes and sequiterpenes.

The smallest reliable fluxes we determined were less than 0.1 nmol m⁻² s⁻¹, as in the case of sesquiterpene emissions from freshly cut grass. Terpenoids, including mono- and sesquiterpenes, were also deposited to the grassland before and after the harvesting. During cutting, total VOC emission fluxes up to 200 nmolC m⁻² s⁻¹ were measured. Methanol emissions accounted for half of the emissions of oxygenated VOCs and a third of the carbon of all measured VOC emissions during harvesting.

Episodical CO2 emission during shoulder seasons in the arctic

DEFF Research Database (Denmark)

Friborg, Thomas; Elberling, Bo; Hansen, Birger

soils. Our knowledge about the exchanges of CO2 and other trace gas fluxes in the arctic region has been constrained by the limited availability of measurements during the long winter season. For that reason only a small number of sites have been able to produce annual budgets of C exchange...... and the driving processes behind winter time exchange of CO2 are not fully understood. Here we present two very different examples of CO2 exchange from shoulder seasons in the Arctic. In an example from NE Greenland, eddy covariance measurements show that the snow cover has a significant effect on the release...... of CO2 during spring. The other example, from a study during late autumn and winter from high arctic Svalbard we found that episodical emissions of CO2 accounted for a significant part of the total CO2 emission form the site. The emission pattern could be associated with temperature variations...

Surprisingly low frequency attenuation effects in long tubes when measuring turbulent fluxes at tall towers

DEFF Research Database (Denmark)

Ibrom, Andreas; Brændholt, Andreas; Pilegaard, Kim

2016-01-01

The eddy covariance technique relies on the fast and accurate measurement of gas concentration fluctuations. While for some gasses robust and compact sensors are available, measurement of, e.g., non CO2 greenhouse gas fluxes is often performed with sensitive equipment that cannot be run on a tower...... without massively disturbing the wind field. To measure CO and N2O fluxes, we installed an eddy covariance system at a 125 m mast, where the gas analyser was kept in a laboratory close to the tower and the sampling was performed using a 150 m long tube with a gas intake at 96 m height. We investigated...... by reducing both the water vapour dilution correction and the cross sensitivity effects on the N2O and CO flux measurements. Here we present the set-up of the concentration step change experiment and its results and compare them with recently developed theories for the behaviour of gases in turbulent tube...

Global Monthly CO2 Flux Inversion Based on Results of Terrestrial Ecosystem Modeling

Science.gov (United States)

Deng, F.; Chen, J.; Peters, W.; Krol, M.

2008-12-01

Most of our understanding of the sources and sinks of atmospheric CO2 has come from inverse studies of atmospheric CO2 concentration measurements. However, the number of currently available observation stations and our ability to simulate the diurnal planetary boundary layer evolution over continental regions essentially limit the number of regions that can be reliably inverted globally, especially over continental areas. In order to overcome these restrictions, a nested inverse modeling system was developed based on the Bayesian principle for estimating carbon fluxes of 30 regions in North America and 20 regions for the rest of the globe. Inverse modeling was conducted in monthly steps using CO2 concentration measurements of 5 years (2000 - 2005) with the following two models: (a) An atmospheric transport model (TM5) is used to generate the transport matrix where the diurnal variation n of atmospheric CO2 concentration is considered to enhance the use of the afternoon-hour average CO2 concentration measurements over the continental sites. (b) A process-based terrestrial ecosystem model (BEPS) is used to produce hourly step carbon fluxes, which could minimize the limitation due to our inability to solve the inverse problem in a high resolution, as the background of our inversion. We will present our recent results achieved through a combination of the bottom-up modeling with BEPS and the top-down modeling based on TM5 driven by offline meteorological fields generated by the European Centre for Medium Range Weather Forecast (ECMFW).

Measurement and modeling of CO2 exchange over forested landscapes in India: an overview

Science.gov (United States)

Kushwaha, S.; Dadhwal, V.

2009-04-01

The increasing atmospheric CO2 concentration and its potential impact on global climate change is the subject of worldwide studies, political debates and international discussions. The concern led to the establishment of the Kyoto Protocol to curtail emissions and mitigate the possible global warming. The studies so far suggest that terrestrial biological sinks might be the low cost options for carbon sequestration, which can be used to partially offset the industrial CO2 emissions globally. In past, the effectiveness of terrestrial sink and the quantitative estimates of their sink strengths have relied mainly on the measurements of changes in carbon stocks across the world. Recent developments in flux tower based measurement techniques such as Eddy Covariance for assessing the CO2, H2O and energy fluxes provide tools for quantifying the net ecosystem exchange (NEE) of CO2 on a continuous basis. These near real time measurements, when integrated with remote sensing, enable the up-scaling of the carbon fluxes to regional scale. More than 470 towers exist worldwide as of now. Indian subcontinent was not having any tower-based CO2 flux measurement system so far. The Indian Space Research Organization under its Geosphere Biosphere Programme is funding five eddy covariance towers for terrestrial CO2 flux measurements in different ecological regions of the country. The tower sites already planned are: (i) a mixed forest plantation (Dalbergia sissoo, Acacia catechu, Holoptelia integrifolia) at Haldwani in collaboration with DISAFRI, University of Tuscia, Italy and the Indian Council for Forestry Research and Education (ICFRE), Dehradun, (ii) a sal (Shorea robusta) forest in Doon valley Himalayan state of Uttarakhand in northern India, (ii) a teak (Tectona grandis) mixed forest at Betul in Madhya Pradesh in central India, (iv) an old teak plantation at Dandeli, and (v) a semi-evergreen forest at Nagarhole in Karnataka state in southern India. The three towers have been

Temporal variations of atmospheric CO2 and CO at Ahmedabad in western India

Science.gov (United States)

Chandra, Naveen; Lal, Shyam; Venkataramani, S.; Patra, Prabir K.; Sheel, Varun

2016-05-01

About 70 % of the anthropogenic carbon dioxide (CO2) is emitted from the megacities and urban areas of the world. In order to draw effective emission mitigation policies for combating future climate change as well as independently validating the emission inventories for constraining their large range of uncertainties, especially over major metropolitan areas of developing countries, there is an urgent need for greenhouse gas measurements over representative urban regions. India is a fast developing country, where fossil fuel emissions have increased dramatically in the last three decades and are predicted to continue to grow further by at least 6 % per year through to 2025. The CO2 measurements over urban regions in India are lacking. To overcome this limitation, simultaneous measurements of CO2 and carbon monoxide (CO) have been made at Ahmedabad, a major urban site in western India, using a state-of-the-art laser-based cavity ring down spectroscopy technique from November 2013 to May 2015. These measurements enable us to understand the diurnal and seasonal variations in atmospheric CO2 with respect to its sources (both anthropogenic and biospheric) and biospheric sinks. The observed annual average concentrations of CO2 and CO are 413.0 ± 13.7 and 0.50 ± 0.37 ppm respectively. Both CO2 and CO show strong seasonality with lower concentrations (400.3 ± 6.8 and 0.19 ± 0.13 ppm) during the south-west monsoon and higher concentrations (419.6 ± 22.8 and 0.72 ± 0.68 ppm) during the autumn (SON) season. Strong diurnal variations are also observed for both the species. The common factors for the diurnal cycles of CO2 and CO are vertical mixing and rush hour traffic, while the influence of biospheric fluxes is also seen in the CO2 diurnal cycle. Using CO and CO2 covariation, we differentiate the anthropogenic and biospheric components of CO2 and found significant contributions of biospheric respiration and anthropogenic emissions in the late night (00:00-05:00 h, IST

On the CO2 exchange between the atmosphere and the biosphere: the role of synoptic and mesoscale processes

International Nuclear Information System (INIS)

Chan, Douglas; Higuchi, Kaz; Shashkov, Alexander; Worthy, Douglas; Liu, Jane; Chen Jing; Yuen Chiu Wai

2004-01-01

Estimating global carbon fluxes by inverting atmospheric CO 2 through the use of atmospheric transport models has shown the importance of the covariance between biospheric fluxes and atmospheric transport on the carbon budget. This covariance or coupling occurs on many time scales. This study examines the coupling of the biosphere and the atmosphere on the meso- and synoptic scales using a coupled atmosphere-biosphere regional model covering Canada. The results are compared with surface and light aircraft measurement campaigns at two boreal forest sites in Canada. Associated with cold and warm frontal features, the model results showed that the biospheric fluxes are strongly coupled to the atmosphere through radiative forcing. The presence of cloud near frontal regions usually results in reduced photosynthetic uptake, producing CO 2 concentration gradients across the frontal regions on the order of 10 parts per million (ppm). Away from the frontal region, the biosphere is coupled to the mesoscale variations in similar ways, resulting in mesoscale variations in CO 2 concentrations of about 5 ppm. The CO 2 field is also coupled strongly to the atmospheric dynamics. In the presence of frontal circulation, the CO 2 near the surface can be transported to the mid to upper troposphere. Mesoscale circulation also plays a significant part in transporting the CO 2 from the planetary boundary layer (PBL) to the mid-troposphere. In the absence of significant mesoscale or synoptic scale circulation, the CO 2 in the PBL has minimal exchange with the free troposphere, leading to strong gradients across the top of the PBL. We speculate that the ubiquity of the common synoptic and mesoscale processes in the atmosphere may contribute significantly to the rectifier effect and hence CO 2 inversion calculations

A two-dimensional hydrodynamic model of turbulent transfer of CO2 and H2O over a heterogeneous land surface

Science.gov (United States)

Mukhartova, Yu. V.; Krupenko, A. S.; Mangura, P. A.; Levashova, N. T.

2018-01-01

A two-dimensional hydrodynamic model was developed and applied to describe turbulent fluxes of CO2 and H2O within the atmospheric surface layer over a heterogeneous land surface featuring mosaic vegetation and complex topography. Numerical experiments were carried out with a 4.5-km profile that crosses a hilly region in the central part of European Russia, with the diverse land-use patterns (bare soil, crop areas, grasslands, and forests). The results showed very strong variability of the vertical and horizontal turbulent CO2 and H2O fluxes. The standard deviations of the vertical fluxes were estimated for separate profile sections with uniform vegetation cover for daylight conditions in summer, and they were comparable with the mean vertical fluxes for corresponding sections. The highest horizontal turbulent fluxes occurred at the boundaries between different plant communities and at irregularities in surface profile. In some cases, these fluxes reached 10-20% of the absolute values of the mean vertical fluxes for corresponding profile sections. Significant errors in estimating the local and integrated fluxes e.g. when using the eddy covariance technique, can result from ignoring the surface topography, even in the case of relatively large plots with uniform vegetation cover.

FLUXNET. Database of fluxes, site characteristics, and flux-community information

Energy Technology Data Exchange (ETDEWEB)

Olson, R. J. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Holladay, S. K. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Cook, R. B. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Falge, E. [Univ. Bayreuth, Bayreuth (Germany); Baldocchi, D. [Univ. of California, Berkeley, CA (United States); Gu, L. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

2004-02-28

FLUXNET is a “network of regional networks” created by international scientists to coordinate regional and global analysis of observations from micrometeorological tower sites. The flux tower sites use eddy covariance methods to measure the exchanges of carbon dioxide (CO₂), water vapor, and energy between terrestrial ecosystems and the atmosphere. FLUXNET’S goals are to aid in understanding the mechanisms controlling the exchanges of CO₂, water vapor, and energy across a range of time (0.5 hours to annual periods) and space scales. FLUXNET provides an infrastructure for the synthesis and analysis of world-wide, long-term flux data compiled from various regional flux networks. Information compiled by the FLUXNET project is being used to validate remote sensing products associated with the National Aeronautics and Space Administration (NASA) Terra and Aqua satellites. FLUXNET provides access to ground information for validating estimates of net primary productivity, and energy absorption that are being generated by the Moderate Resolution Imaging Spectroradiometer (MODIS) sensors. In addition, this information is also used to develop and validate ecosystem models.

AFCI-2.0 Neutron Cross Section Covariance Library

Energy Technology Data Exchange (ETDEWEB)

Herman, M.; Herman, M; Oblozinsky, P.; Mattoon, C.M.; Pigni, M.; Hoblit, S.; Mughabghab, S.F.; Sonzogni, A.; Talou, P.; Chadwick, M.B.; Hale, G.M.; Kahler, A.C.; Kawano, T.; Little, R.C.; Yount, P.G.

2011-03-01

materials and fission products, and 20 actinides. Covariances are given in 33-energy groups, from 10?5 eV to 19.6 MeV, obtained by processing with LANL processing code NJOY using 1/E flux. In addition to these 110 files, the library contains 20 files with nu-bar covariances, 3 files with covariances of prompt fission neutron spectra (238,239,240-Pu), and 2 files with mu-bar covariances (23-Na, 56-Fe). Over the period of three years several working versions of the library have been released and tested by ANL and INL reactor analysts. Useful feedback has been collected allowing gradual improvements of the library. In addition, QA system was developed to check basic properties and features of the whole library, allowing visual inspection of uncertainty and correlations plots, inspection of uncertainties of integral quantities with independent databases, and dispersion of cross sections between major evaluated libraries. The COMMARA-2.0 beta version of the library was released to ANL and INL reactor analysts in October 2010. The final version, described in the present report, was released in March 2011.

AFCI-2.0 Neutron Cross Section Covariance Library

International Nuclear Information System (INIS)

Herman, M.; Oblozinsky, P.; Mattoon, C.M.; Pigni, M.; Hoblit, S.; Mughabghab, S.F.; Sonzogni, A.; Talou, P.; Chadwick, M.B.; Hale, G.M.; Kahler, A.C.; Kawano, T.; Little, R.C.; Yount, P.G.

2011-01-01

structural materials and fission products, and 20 actinides. Covariances are given in 33-energy groups, from 10?5 eV to 19.6 MeV, obtained by processing with LANL processing code NJOY using 1/E flux. In addition to these 110 files, the library contains 20 files with nu-bar covariances, 3 files with covariances of prompt fission neutron spectra (238,239,240-Pu), and 2 files with mu-bar covariances (23-Na, 56-Fe). Over the period of three years several working versions of the library have been released and tested by ANL and INL reactor analysts. Useful feedback has been collected allowing gradual improvements of the library. In addition, QA system was developed to check basic properties and features of the whole library, allowing visual inspection of uncertainty and correlations plots, inspection of uncertainties of integral quantities with independent databases, and dispersion of cross sections between major evaluated libraries. The COMMARA-2.0 beta version of the library was released to ANL and INL reactor analysts in October 2010. The final version, described in the present report, was released in March 2011.

Ocean-Atmosphere CO2 Fluxes in the North Atlantic Subtropical Gyre: Association with Biochemical and Physical Factors during Spring

Directory of Open Access Journals (Sweden)

Macarena Burgos

2015-08-01

Full Text Available Sea surface partial pressure of CO2 (pCO2 was measured continuously in a transect of the North Atlantic subtropical gyre between Santo Domingo, Dominican Republic (18.1° N, 68.5° W and Vigo, Spain (41.9° N, 11.8° W during spring 2011. Additional biogeochemical and physical variables measured to identify factors controlling the surface pCO2 were analyzed in discrete samples collected at 16 sites along the transect at the surface and to a depth of 200 m. Sea surface pCO2 varied between 309 and 662 μatm, and showed differences between the western and eastern subtropical gyre. The subtropical gyre acted as a net CO2 sink, with a mean flux of −5.5 ± 2.2 mmol m−2 day−1. The eastern part of the transect, close to the North Atlantic Iberian upwelling off the Galician coast, was a CO2 source with an average flux of 33.5 ± 9.0 mmol m−2 day−1. Our results highlight the importance of making more surface pCO2 observations in the area located east of the Azores Islands since air-sea CO2 fluxes there are poorly studied.

Quantification of fossil fuel CO2 emissions at the urban scale: Results from the Indianapolis Flux Project (INFLUX)

Science.gov (United States)

Turnbull, J. C.; Cambaliza, M. L.; Sweeney, C.; Karion, A.; Newberger, T.; Tans, P. P.; Lehman, S.; Davis, K. J.; Miles, N. L.; Richardson, S.; Lauvaux, T.; Shepson, P.; Gurney, K. R.; Song, Y.; Razlivanov, I. N.

2012-12-01

Emissions of fossil fuel CO2 (CO2ff) from anthropogenic sources are the primary driver of observed increases in the atmospheric CO2 burden, and hence global warming. Quantification of the magnitude of fossil fuel CO2 emissions is vital to improving our understanding of the global and regional carbon cycle, and independent evaluation of reported emissions is essential to the success of any emission reduction efforts. The urban scale is of particular interest, because ~75% CO2ff is emitted from urban regions, and cities are leading the way in attempts to reduce emissions. Measurements of 14CO2 can be used to determine CO2ff, yet existing 14C measurement techniques require laborious laboratory analysis and measurements are often insufficient for inferring an urban emission flux. This presentation will focus on how 14CO2 measurements can be combined with those of more easily measured ancillary tracers to obtain high resolution CO2ff mixing ratio estimates and then infer the emission flux. A pilot study over Sacramento, California showed strong correlations between CO2ff and carbon monoxide (CO) and demonstrated an ability to quantify the urban flux, albeit with large uncertainties. The Indianapolis Flux Project (INFLUX) aims to develop and assess methods to quantify urban greenhouse gas emissions. Indianapolis was chosen as an ideal test case because it has relatively straightforward meteorology; a contained, isolated, urban region; and substantial and well-known fossil fuel CO2 emissions. INFLUX incorporates atmospheric measurements of a suite of gases and isotopes including 14C from light aircraft and from a network of existing tall towers surrounding the Indianapolis urban area. The recently added CO2ff content is calculated from measurements of 14C in CO2, and then convolved with atmospheric transport models and ancillary data to estimate the urban CO2ff emission flux. Significant innovations in sample collection include: collection of hourly averaged samples to

Structure and magnetic properties of flux grown single crystals of Co3-xFexSn2S2 shandites

Science.gov (United States)

Kassem, Mohamed A.; Tabata, Yoshikazu; Waki, Takeshi; Nakamura, Hiroyuki

2016-01-01

We report a successful single crystal growth of the shandite-type half-metallic ferromagnet Co3Sn2S2, and its Fe-substituted compounds, Co3-xFexSn2S2, by employing the flux method. Although Fe3Sn2S2 is unstable phase, we found that using the self Sn flux enables us to obtain single phase crystals up to x=0.53. The chemical composition of the grown plate-shaped single crystals was examined using wavelength-dispersive X-ray spectroscopy. The shandite structure with R 3 ̅m symmetry was confirmed by powder X-ray diffraction and the crystal structure parameters were refined using the Rietveld method. Magnetization measurements show suppression of the ferromagnetic order upon Fe-substitution , as well as in other substituted systems such as In- and Ni-substituted Co3Sn2S2. The almost identical magnetic phase diagrams of the Fe- and In-substituted compounds indicate that the electron number is dominantly significant to the magnetism in the Co-based shandite.

CO and H2 uptake and emissions by soil: variability of fluxes and their isotopic signatures

Science.gov (United States)

Popa, Maria Elena; Chen, Qianjie; Ferrero Lopez, Noelia; Röckmann, Thomas

2017-04-01

In order to study the uptake and release of H2 and CO by soil, we performed long term, high frequency measurements with an automatic soil chamber at two sites in the Netherlands (Cabauw - grassland, and Speuld - forest). The measurements were performed over different seasons and cover in total a cumulated interval of about one year. These measurements allow determining separately, for each species, the two distinct fluxes i.e. uptake and release, and investigating their temporal variability and dependencies on environmental variables. Additional experiments were performed for determining the isotopic signatures of the H2 and CO uptake and release by soil. Flask samples were filled from the soil chamber, and then analyzed in the laboratory for the stable isotopic composition of H2 (δD) and CO (δ13C and δ18O). We find that both uptake and release are present at all times, regardless of the direction of the net flux. The emissions are significant for both species and at Cabauw, there are times and places where emissions outweigh the soil uptake. For each species, the two fluxes have different behavior and dependence on external variables, which indicates that they have different origins. The isotope results also support that, for both H2 and CO, uptake and emission occur simultaneously. We were able to determine separately the isotopic effects of the two fluxes. For both H2 and CO, soil uptake is associated with a small positive fractionation (the lighter molecule is taken up faster). The soil uptake fractionation (α = kheavy/klight) was 0.945 ± 0.004 for H2; for CO, the fractionation was 0.992 for 13C and 0.985 for 18O. The isotopic composition of the H2 emitted from the grassland was -530 ± 40 ‰, less depleted that what is expected from the isotopic equilibrium of H2 with water. For CO, the isotopic composition of the soil emission is depleted in 13C compared to atmospheric CO, and lower than the average isotopic composition of plant or soil organic matter.

Estimates of CO2 fluxes over the city of Cape Town, South Africa, through Bayesian inverse modelling

Science.gov (United States)

Nickless, Alecia; Rayner, Peter J.; Engelbrecht, Francois; Brunke, Ernst-Günther; Erni, Birgit; Scholes, Robert J.

2018-04-01

We present a city-scale inversion over Cape Town, South Africa. Measurement sites for atmospheric CO2 concentrations were installed at Robben Island and Hangklip lighthouses, located downwind and upwind of the metropolis. Prior estimates of the fossil fuel fluxes were obtained from a bespoke inventory analysis where emissions were spatially and temporally disaggregated and uncertainty estimates determined by means of error propagation techniques. Net ecosystem exchange (NEE) fluxes from biogenic processes were obtained from the land atmosphere exchange model CABLE (Community Atmosphere Biosphere Land Exchange). Uncertainty estimates were based on the estimates of net primary productivity. CABLE was dynamically coupled to the regional climate model CCAM (Conformal Cubic Atmospheric Model), which provided the climate inputs required to drive the Lagrangian particle dispersion model. The Bayesian inversion framework included a control vector where fossil fuel and NEE fluxes were solved for separately.Due to the large prior uncertainty prescribed to the NEE fluxes, the current inversion framework was unable to adequately distinguish between the fossil fuel and NEE fluxes, but the inversion was able to obtain improved estimates of the total fluxes within pixels and across the domain. The median of the uncertainty reductions of the total weekly flux estimates for the inversion domain of Cape Town was 28 %, but reach as high as 50 %. At the pixel level, uncertainty reductions of the total weekly flux reached up to 98 %, but these large uncertainty reductions were for NEE-dominated pixels. Improved corrections to the fossil fuel fluxes would be possible if the uncertainty around the prior NEE fluxes could be reduced. In order for this inversion framework to be operationalised for monitoring, reporting, and verification (MRV) of emissions from Cape Town, the NEE component of the CO2 budget needs to be better understood. Additional measurements of Δ14C and δ13C isotope

Net uptake of atmospheric CO2 by coastal submerged aquatic vegetation

Science.gov (United States)

Tokoro, Tatsuki; Hosokawa, Shinya; Miyoshi, Eiichi; Tada, Kazufumi; Watanabe, Kenta; Montani, Shigeru; Kayanne, Hajime; Kuwae, Tomohiro

2014-01-01

‘Blue Carbon’, which is carbon captured by marine living organisms, has recently been highlighted as a new option for climate change mitigation initiatives. In particular, coastal ecosystems have been recognized as significant carbon stocks because of their high burial rates and long-term sequestration of carbon. However, the direct contribution of Blue Carbon to the uptake of atmospheric CO2 through air-sea gas exchange remains unclear. We performed in situ measurements of carbon flows, including air-sea CO2 fluxes, dissolved inorganic carbon changes, net ecosystem production, and carbon burial rates in the boreal (Furen), temperate (Kurihama), and subtropical (Fukido) seagrass meadows of Japan from 2010 to 2013. In particular, the air-sea CO2 flux was measured using three methods: the bulk formula method, the floating chamber method, and the eddy covariance method. Our empirical results show that submerged autotrophic vegetation in shallow coastal waters can be functionally a sink for atmospheric CO2. This finding is contrary to the conventional perception that most near-shore ecosystems are sources of atmospheric CO2. The key factor determining whether or not coastal ecosystems directly decrease the concentration of atmospheric CO2 may be net ecosystem production. This study thus identifies a new ecosystem function of coastal vegetated systems; they are direct sinks of atmospheric CO2. PMID:24623530