Ecosystem transpiration and evaporation: Insights from three water flux partitioning methods across FLUXNET sites
Nelson, Jacob A. ; Pérez-Priego, Oscar ; Zhou, Sha ; Poyatos, Rafael ; Zhang, Yao ; Blanken, Peter D. ; Gimeno, Teresa E. ; Wohlfahrt, Georg ; Desai, Ankur R. ; Gioli, Beniamino ; Limousin, Jean Marc ; Bonal, Damien ; Paul-Limoges, Eugénie ; Scott, Russell L. ; Varlagin, Andrej ; Fuchs, Kathrin ; Montagnani, Leonardo ; Wolf, Sebastian ; Delpierre, Nicolas ; Berveiller, Daniel ; Gharun, Mana ; Belelli Marchesini, Luca ; Gianelle, Damiano ; Šigut, Ladislav ; Mammarella, Ivan ; Siebicke, Lukas ; Black, T.B. ; Knohl, Alexander ; Hörtnagl, Lukas ; Magliulo, Vincenzo ; Besnard, Simon ; Weber, Ulrich ; Carvalhais, Nuno ; Migliavacca, Mirco ; Reichstein, Markus ; Jung, Martin - \ 2020
Global Change Biology (2020). - ISSN 1354-1013
ecohydrology - eddy covariance - evaporation - evapotranspiration - FLUXNET - transpiration
We apply and compare three widely applicable methods for estimating ecosystem transpiration (T) from eddy covariance (EC) data across 251 FLUXNET sites globally. All three methods are based on the coupled water and carbon relationship, but they differ in assumptions and parameterizations. Intercomparison of the three daily T estimates shows high correlation among methods (R between.89 and.94), but a spread in magnitudes of T/ET (evapotranspiration) from 45% to 77%. When compared at six sites with concurrent EC and sap flow measurements, all three EC-based T estimates show higher correlation to sap flow-based T than EC-based ET. The partitioning methods show expected tendencies of T/ET increasing with dryness (vapor pressure deficit and days since rain) and with leaf area index (LAI). Analysis of 140 sites with high-quality estimates for at least two continuous years shows that T/ET variability was 1.6 times higher across sites than across years. Spatial variability of T/ET was primarily driven by vegetation and soil characteristics (e.g., crop or grass designation, minimum annual LAI, soil coarse fragment volume) rather than climatic variables such as mean/standard deviation of temperature or precipitation. Overall, T and T/ET patterns are plausible and qualitatively consistent among the different water flux partitioning methods implying a significant advance made for estimating and understanding T globally, while the magnitudes remain uncertain. Our results represent the first extensive EC data-based estimates of ecosystem T permitting a data-driven perspective on the role of plants’ water use for global water and carbon cycling in a changing climate.
Altered energy partitioning across terrestrial ecosystems in the European drought year 2018
Graf, Alexander ; Klosterhalfen, Anne ; Arriga, Nicola ; Bernhofer, Christian ; Bogena, Heye ; Bornet, Frédéric ; Brüggemann, Nicolas ; Brümmer, Christian ; Buchmann, Nina ; Chi, Jinshu ; Chipeaux, Christophe ; Cremonese, Edoardo ; Cuntz, Matthias ; Dušek, Jiří ; El-Madany, Tarek S. ; Fares, Silvano ; Fischer, Milan ; Foltýnová, Lenka ; Gharun, Mana ; Ghiasi, Shiva ; Gielen, Bert ; Gottschalk, Pia ; Grünwald, Thomas ; Heinemann, Günther ; Heinesch, Bernard ; Heliasz, Michal ; Holst, Jutta ; Hörtnagl, Lukas ; Ibrom, Andreas ; Ingwersen, Joachim ; Jurasinski, Gerald ; Klatt, Janina ; Knohl, Alexander ; Koebsch, Franziska ; Konopka, Jan ; Korkiakoski, Mika ; Kowalska, Natalia ; Kremer, Pascal ; Kruijt, Bart ; Lafont, Sebastien ; Léonard, Joël ; Ligne, Anne De; Longdoz, Bernard ; Loustau, Denis ; Magliulo, Vincenzo ; Mammarella, Ivan ; Manca, Giovanni ; Mauder, Matthias ; Migliavacca, Mirco ; Mölder, Meelis ; Neirynck, Johan ; Ney, Patrizia ; Nilsson, Mats ; Paul-Limoges, Eugénie ; Peichl, Matthias ; Pitacco, Andrea ; Poyda, Arne ; Rebmann, Corinna ; Roland, Marilyn ; Sachs, Torsten ; Schmidt, Marius ; Schrader, Frederik ; Siebicke, Lukas ; Šigut, Ladislav ; Tuittila, Eeva Stiina ; Varlagin, Andrej ; Vendrame, Nadia ; Vincke, Caroline ; Völksch, Ingo ; Weber, Stephan ; Wille, Christian ; Wizemann, Hans Dieter ; Zeeman, Matthias ; Vereecken, Harry - \ 2020
Philosophical Transactions of the Royal Society B. Biological sciences 375 (2020)1810. - ISSN 0962-8436 - 1 p.
eddy covariance - energy balance - evapotranspiration - heat flux - net carbon uptake - water-use efficiency
Drought and heat events, such as the 2018 European drought, interact with the exchange of energy between the land surface and the atmosphere, potentially affecting albedo, sensible and latent heat fluxes, as well as CO2 exchange. Each of these quantities may aggravate or mitigate the drought, heat, their side effects on productivity, water scarcity and global warming. We used measurements of 56 eddy covariance sites across Europe to examine the response of fluxes to extreme drought prevailing most of the year 2018 and how the response differed across various ecosystem types (forests, grasslands, croplands and peatlands). Each component of the surface radiation and energy balance observed in 2018 was compared to available data per site during a reference period 2004-2017. Based on anomalies in precipitation and reference evapotranspiration, we classified 46 sites as drought affected. These received on average 9% more solar radiation and released 32% more sensible heat to the atmosphere compared to the mean of the reference period. In general, drought decreased net CO2 uptake by 17.8%, but did not significantly change net evapotranspiration. The response of these fluxes differed characteristically between ecosystems; in particular, the general increase in the evaporative index was strongest in peatlands and weakest in croplands. This article is part of the theme issue 'Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale'.
Winter respiratory C losses provide explanatory power for net ecosystem productivity
Haeni, M. ; Zweifel, R. ; Eugster, W. ; Gessler, A. ; Zielis, S. ; Bernhofer, C. ; Carrara, A. ; Grünwald, T. ; Havránková, K. ; Heinesch, B. ; Marek, M. ; Moors, E. ; Schelhaas, M.J. ; Buchmann, N. - \ 2017
Journal of Geophysical Research: Biogeosciences 122 (2017)1. - ISSN 2169-8953 - p. 243 - 260.
carbon sink - carbon source - CO exchange - eddy covariance - growing season length - winter respiration
Accurate predictions of net ecosystem productivity (NEPc) of forest ecosystems are essential for climate change decisions and requirements in the context of national forest growth and greenhouse gas inventories. However, drivers and underlying mechanisms determining NEPc (e.g., climate and nutrients) are not entirely understood yet, particularly when considering the influence of past periods. Here we explored the explanatory power of the compensation day (cDOY)—defined as the day of year when winter net carbon losses are compensated by spring assimilation—for NEPc in 26 forests in Europe, North America, and Australia, using different NEPc integration methods. We found cDOY to be a particularly powerful predictor for NEPc of temperate evergreen needleleaf forests (R2 = 0.58) and deciduous broadleaf forests (R2 = 0.68). In general, the latest cDOY correlated with the lowest NEPc. The explanatory power of cDOY depended on the integration method for NEPc, forest type, and whether the site had a distinct winter net respiratory carbon loss or not. The integration methods starting in autumn led to better predictions of NEPc from cDOY then the classical calendar method starting 1 January. Limited explanatory power of cDOY for NEPc was found for warmer sites with no distinct winter respiratory loss period. Our findings highlight the importance of the influence of winter processes and the delayed responses of previous seasons' climatic conditions on current year's NEPc. Such carry-over effects may contain information from climatic conditions, carbon storage levels, and hydraulic traits of several years back in time.
Atmospheric turbulence over crops : confronting theories with observations
Boer, A. van de - \ 2015
Wageningen University. Promotor(en): Bert Holtslag, co-promotor(en): Arnold Moene; A. Graf. - Wageningen : Wageningen University - ISBN 9789462572416 - 143
turbulentie - meteorologie - atmosfeer - gewassen - watergebruiksrendement - transpiratie - modellen - eddy-covariantie - turbulente stroming - turbulence - meteorology - atmosphere - crops - water use efficiency - transpiration - models - eddy covariance - turbulent flow
Atmospheric turbulence plays a key role in hydrological and carbon cycles, and in weather and climate. Understanding and forecasting turbulence is thereby relevant for human life and environment.
We deal with some major challenges for studying atmospheric turbulence over crops. Land-atmosphere interactions are specifically complex because of surface heterogeneity. Also, boundary-layer entrainment complicates measuring and studying surface fluxes. Furthermore, the absence of high-frequency observations and of measurements of underlying soil and vegetation processes impedes studying land-atmosphere interactions.
We show the applicability of analytical footprint models over a heterogeneous land surface, and the validity of Monin-Obukhov similarity theory for a strongly-convective boundary-layer. Moreover, we present improvements on a scheme that can be used to estimate the amount of atmospheric turbulence from single-level weather data. We furthermore suggest to improve the partitioning theory that is used to distinguish soil processes from plant processes in eddy-covariance flux observations.
The use of radiocarbon to constrain current and future soil organic matter turnover and transport in a temperate forest
Braakhekke, M.C. ; Beer, C. ; Schrumpf, M. ; Ahrens, B. ; Hoosbeek, M.R. ; Kruijt, B. ; Kabat, P. ; Reichstein, M. ; Ekici, A. - \ 2014
Journal of Geophysical Research: Biogeosciences 119 (2014)3. - ISSN 2169-8953 - p. 372 - 391.
global vegetation models - terrestrial carbon-cycle - climate-change - age calibration - vertical-distribution - eddy covariance - residence times - c-14 data - storage - co2
We investigated the merits of radiocarbon measurements for estimating soil organic matter (SOM) turnover and vertical transport for a temperate deciduous forest in Germany. Eleven parameters, defining decomposition and transport in the soil carbon model SOMPROF, were estimated using a Bayesian approach based on organic carbon measurements and radiocarbon concentration of SOM and heterotrophic respiration. The addition of radiocarbon data had strong effects on the parameters, most importantly a reduction of the decomposition and production rate of the slowest SOM pool by an order of magnitude, and a similar reduction in advective SOM transport. The modified parameters further led to changes in the partitioning of SOM over the different model pools. The calibration results were subsequently used to perform transient soil carbon projections for the period 1901–2100. These simulations were run with parameter sets from calibrations both with and without radiocarbon. The results show an increase over time of topsoil carbon and a decrease in the subsoil, adding to a net gain overall. Near the end of the 21st century, total carbon stocks stabilize and—for the radiocarbon-constrained model—start to decrease. However, the changes are small compared to the total stocks. The model results for the calibrations with and without radiocarbon are in general quite similar, but the latter shows notably higher heterotrophic respiration fluxes. Constraining the model with radiocarbon yielded only a small reduction of uncertainty for the total carbon stocks, while for the individual depth compartments, the uncertainty was¿increased.
Agricultural peatlands: towards a greenhouse gas sink - a synthesis of a Dutch landscape study
Schrier-Uijl, A.P. ; Kroon, P.S. ; Hendriks, D.M.D. ; Hensen, A. ; Huissteden, J. van; Leffelaar, P.A. ; Berendse, F. ; Veenendaal, E.M. - \ 2014
Biogeosciences 11 (2014). - ISSN 1726-4170 - p. 4559 - 4576.
anemometer (co)sine response - covariance flux measurements - cut-away peatland - eddy covariance - carbon balance - water-vapor - n2o - exchange - meadow - soil
It is generally known that managed, drained peatlands act as carbon (C) sources. In this study we examined how mitigation through the reduction of the intensity of land management and through rewetting may affect the greenhouse gas (GHG) emission and the C balance of intensively managed, drained, agricultural peatlands. Carbon and GHG balances were determined for three peatlands in the western part of the Netherlands from 2005 to 2008 by considering spatial and temporal variability of emissions (CO2, CH4 and N2O). One area (Oukoop) is an intensively managed grass-on-peatland area, including a dairy farm, with the ground water level at an average annual depth of 0.55 (±0.37) m below the soil surface. The second area (Stein) is an extensively managed grass-on-peatland area, formerly intensively managed, with a dynamic ground water level at an average annual depth of 0.45 (±0.35) m below the soil surface. The third area is a (since 1998) rewetted former agricultural peatland (Horstermeer), close to Oukoop and Stein, with the average annual ground water level at a depth of 0.2 (±0.20) m below the soil surface. During the measurement campaigns we found that both agriculturally managed sites acted as C and GHG sources and the rewetted former agricultural peatland acted as a C and GHG sink. The ecosystem (fields and ditches) total GHG balance, including CO2, CH4 and N2O, amounted to 3.9 (±0.4), 1.3 (±0.5) and -1.7 (±1.8) g CO2-eq m-2 d-1 for Oukoop, Stein and Horstermeer, respectively. Adding the farm-based emissions to Oukoop and Stein resulted in a total GHG emission of 8.3 (±1.0) and 6.6 (±1.3) g CO2-eq m-2 d-1, respectively. For Horstermeer the GHG balance remained the same since no farm-based emissions exist. Considering the C balance (uncertainty range 40–60%), the total C release in Oukoop and Stein is 5270 and 6258 kg C ha-1 yr-1, respectively (including ecosystem and management fluxes), and the total C uptake in Horstermeer is 3538 kg C ha-1 yr-1. Water bodies contributed significantly to the terrestrial GHG balance because of a high release of CH4. Overall, this study suggests that managed peatlands are large sources of GHGs and C, but, if appropriate measures are taken, they can be turned back into GHG and C sinks within 15 years of abandonment and rewetting. The shift from an intensively managed grass-on-peat area (Oukoop) to an extensively managed one (Stein) reduced the GHG emissions mainly because N2O emission and farm-based CH4 emissions decreased.
Redefinition and global estimation of basal ecosystem respiration rate
Jacobs, C.M.J. ; Yuan, W. - \ 2011
Global Biogeochemical Cycles 25 (2011). - ISSN 0886-6236
carbon-dioxide flux - soil respiration - eddy covariance - temperature sensitivity - interannual variability - co2 exchange - deciduous forest - climate-change - mediterranean forest - european forests
Basal ecosystem respiration rate (BR), the ecosystem respiration rate at a given temperature, is a common and important parameter in empirical models for quantifying ecosystem respiration (ER) globally. Numerous studies have indicated that BR varies in space. However, many empirical ER models still use a global constant BR largely due to the lack of a functional description for BR. In this study, we redefined BR to be ecosystem respiration rate at the mean annual temperature. To test the validity of this concept, we conducted a synthesis analysis using 276 site-years of eddy covariance data, from 79 research sites located at latitudes ranging from similar to 3 degrees S to similar to 70 degrees N. Results showed that mean annual ER rate closely matches ER rate at mean annual temperature. Incorporation of site-specific BR into global ER model substantially improved simulated ER compared to an invariant BR at all sites. These results confirm that ER at the mean annual temperature can be considered as BR in empirical models. A strong correlation was found between the mean annual ER and mean annual gross primary production (GPP). Consequently, GPP, which is typically more accurately modeled, can be used to estimate BR. A light use efficiency GPP model (i.e., EC-LUE) was applied to estimate global GPP, BR and ER with input data from MERRA (Modern Era Retrospective-Analysis for Research and Applications) and MODIS (Moderate resolution Imaging Spectroradiometer). The global ER was 103 Pg C yr (-1), with the highest respiration rate over tropical forests and the lowest value in dry and high-latitude areas.
Longer growing seasons do not increase net carbon uptake in Northeastern Siberian tundra
Parmentier, F.J.W. ; Molen, M.K. van der; Huissteden, J. van; Karsanaev, S. ; Kononov, A.V. ; Suzdalov, D. ; Maximov, T.C. ; Dolman, A.J. - \ 2011
Journal of Geophysical Research: Biogeosciences 116 (2011). - ISSN 2169-8953 - 11 p.
eddy covariance - ecosystem exchange - climate-change - arctic tundra - co2 exchange - respiration - flux - vegetation - dioxide - cycle
With global warming, snowmelt is occurring earlier and growing seasons are becoming longer around the Arctic. It has been suggested that this would lead to more uptake of carbon due to a lengthening of the period in which plants photosynthesize. To investigate this suggestion, 8 consecutive years of eddy covariance measurements at a northeastern Siberian graminoid tundra site were investigated for patterns in net ecosystem exchange, gross primary production (GPP) and ecosystem respiration (Reco). While GPP showed no clear increase with longer growing seasons, it was significantly increased in warmer summers. Due to these warmer temperatures however, the increase in uptake was mostly offset by an increase in Reco. Therefore, overall variability in net carbon uptake was low, and no relationship with growing season length was found. Furthermore, the highest net uptake of carbon occurred with the shortest and the coldest growing season. Low uptake of carbon mostly occurred with longer or warmer growing seasons. We thus conclude that the net carbon uptake of this ecosystem is more likely to decrease rather than to increase under a warmer climate. These results contradict previous research that has showed more net carbon uptake with longer growing seasons. We hypothesize that this difference is due to site-specific differences, such as climate type and soil, and that changes in the carbon cycle with longer growing seasons will not be uniform around the Arctic
Management effects on net ecosystem carbon and GHG budgets at European crop sites
Ceschia, E. ; Beziat, P. ; Dejoux, J.F. ; Elbers, J.A. ; Jacobs, C.M.J. ; Jans, W.W.P. - \ 2010
Agriculture, Ecosystems and Environment 139 (2010)3. - ISSN 0167-8809 - p. 363 - 383.
rain-fed maize - greenhouse-gas emissions - north central region - soil organic-carbon - no-till ecosystem - eddy covariance - dioxide exchange - co2 flux - terrestrial ecosystems - biome productivity
The greenhouse gas budgets of 15 European crop sites covering a large climatic gradient and corresponding to 41 site-years were estimated. The sites included a wide range of management practices (organic and/or mineral fertilisation, tillage or ploughing, with or without straw removal, with or without irrigation, etc.) and were cultivated with 15 representative crop species common to Europe. At all sites, carbon inputs (organic fertilisation and seeds), carbon exports (harvest or fire) and net ecosystem production (NEP), measured with the eddy covariance technique, were calculated. The variability of the different terms and their relative contributions to the net ecosystem carbon budget (NECB) were analysed for all site-years, and the effect of management on NECB was assessed. To account for greenhouse gas (GHG) fluxes that were not directly measured on site, we estimated the emissions caused by field operations (EFO) for each site using emission factors from the literature. The EFO were added to the NECB to calculate the total GHG budget (GHGB) for a range of cropping systems and management regimes. N2O emissions were calculated following the IPCC (2007) guidelines, and CH4 emissions were estimated from the literature for the rice crop site only. At the other sites, CH4 emissions/oxidation were assumed to be negligible compared to other contributions to the net GHGB. Finally, we evaluated crop efficiencies (CE) in relation to global warming potential as the ratio of C exported from the field (yield) to the total GHGB. On average, NEP was negative (-284 ± 228 g C m-2 year-1), and most cropping systems behaved as atmospheric sinks, with sink strength generally increasing with the number of days of active vegetation. The NECB was, on average, 138 ± 239 g C m-2 year-1, corresponding to an annual loss of about 2.6 ± 4.5% of the soil organic C content, but with high uncertainty. Management strongly influenced the NECB, with organic fertilisation tending to lower the ecosystem carbon budget. On average, emissions caused by fertilisers (manufacturing, packaging, transport, storage and associated N2O emissions) represented close to 76% of EFO. The operation of machinery (use and maintenance) and the use of pesticides represented 9.7 and 1.6% of EFO, respectively. On average, the NEP (through uptake of CO2) represented 88% of the negative radiative forcing, and exported C represented 88% of the positive radiative forcing of a mean total GHGB of 203 ± 253 g C-eq m-2 year-1. Finally, CE differed considerably among crops and according to management practices within a single crop. Because the CE was highly variable, it is not suitable at this stage for use as an emission factor for management recommendations, and more studies are needed to assess the effects of management on crop efficiency.
Carbon exchange of a maize (Zea mays L.) crop: Influence of phenology
Jans, W.W.P. ; Jacobs, C.M.J. ; Kruijt, B. ; Elbers, J.A. ; Barendse, S.C.A. ; Moors, E.J. - \ 2010
Agriculture, Ecosystems and Environment 139 (2010)3. - ISSN 0167-8809 - p. 316 - 324.
netto ecosysteem uitwisseling - koolstofvastlegging - fenologie - rogge - maïs - zea mays - organische meststoffen - nederland - net ecosystem exchange - carbon sequestration - phenology - rye - maize - zea mays - organic fertilizers - netherlands - gross primary production - rain-fed maize - ecosystem respiration - dioxide exchange - eddy covariance - soil respiration - growing-season - use efficiency - united-states - phase-change
A study was carried out to quantify the carbon budget of a maize (Zea mays L.) crop followed by a rye cover crop in the Netherlands, and to determine the importance of the phenological phases and the fallow phase when modelling the carbon budget. Measurements were made of carbon fluxes, soil respiration, biomass and Plant Area Index (PAI). On the basis of PAI the annual cycle was subdivided into 5 phases: juvenile-vegetative, adult-vegetative, reproductive, senescence and fallow. To model the annual carbon budget, it should be sufficient to assess the light response in the juvenile-vegetative phase, the growing season and the fallow phase, combined with the length of these phases and the PAI development. We conclude that emphasis should be put on determining off-season fluxes while the growing season can be estimated from radiation only. During the cultivation period (from sowing to harvest) 5.97 tC ha−1 was sequestered by the maize crop. The amount of carbon exported from the field was 7.5 tC ha−1, and the estimated amount of carbon imported by organic fertilizer was 0.51 tC ha−1, resulting in a carbon loss of 1.02 tC ha−1 from the soil. The fallow phase, with a rye cover crop at the field, decreased the amount of carbon fixed in the cultivation period by 2.65 tC ha−1 (44% reduction). To enable determination of the carbon sequestration or emission of croplands, farmers should be required to analyze, apart from the nitrogen content, also the carbon content of organic fertilizers.
A study was carried out to quantify the carbon budget of a maize (Zea mays L) crop followed by a rye cover crop in the Netherlands, and to determine the importance of the phenological phases and the fallow phase when modelling the carbon budget. Measurements were made of carbon fluxes, soil respiration, biomass and Plant Area Index (PAI). On the basis of PAI the annual cycle was subdivided into 5 phases: juvenile-vegetative, adult-vegetative, reproductive, senescence and fallow. To model the annual carbon budget, it should be sufficient to assess the light response in the juvenile-vegetative phase, the growing season and the fallow phase, combined with the length of these phases and the PAI development. We conclude that emphasis should be put on determining off-season fluxes while the growing season can be estimated from radiation only. During the cultivation period (from sowing to harvest) 5.97 tC ha(-1) was sequestered by the maize crop. The amount of carbon exported from the field was 7.5 tC ha(-1), and the estimated amount of carbon imported by organic fertilizer was 0.51 tC ha(-1), resulting in a carbon loss of 1.02 tC ha(-1) from the soil. The fallow phase, with a rye cover crop at the field, decreased the amount of carbon fixed in the cultivation period by 2.65 tC ha(-1) (44% reduction). To enable determination of the carbon sequestration or emission of croplands, farmers should be required to analyze, apart from the nitrogen content, also the carbon content of organic fertilizers. (C) 2010 Elsevier B.V. All rights reserved.
Measurements necessary for assessing the net ecosystem carbon budget of ceoplands
Smith, P. ; Lanigan, G. ; Kutsch, W.L. ; Moors, E.J. - \ 2010
Agriculture, Ecosystems and Environment 139 (2010)3. - ISSN 0167-8809 - p. 302 - 315.
netto ecosysteem koolstofbalans - broeikasgassen - meetsystemen - eddy-covariantie - landbouwgrond - gewasproductie - net ecosystem carbon balance - greenhouse gases - measurement systems - eddy covariance - agricultural land - crop production - soil organic-matter - eddy-correlation measurements - covariance flux measurements - bornhoved lake district - closed dynamic chambers - long-term experiments - land-use change - co2 efflux - agricultural soils - elevated co2
There are a number of methods that can be used to help assess carbon budgets at the site to continental scales. Eddy covariance (EC) networks have been developed over the last decade and have been used to make many advances in our understanding. However, eddy covariance measurements of CO2 and water vapour exchanges quantify the fluxes only on short time scales, but do not assess the impacts of long-term processes that contribute to biogeochemical cycling in croplands, such as harvest or residue removal and other management practices, so many other supplementary measurements are required to attribute different components of the carbon flux. Such methods include isotope studies, chamber flux measurements of C and other greenhouse gases, inventories of above- and below-ground biomass as well as management in- and outputs, book-keeping modelling, process modelling, experimental manipulation and earth observation (e.g. remote sensing). In this review, we summarise the component fluxes that make up the total cropland carbon budget, describe the key fluxes and methods used to estimate them, and examine how they need to be integrated to obtain the net ecosystem carbon budget of European croplands. We describe the uncertainties and difficulties inherent at each stage and how these can be minimised.
Productivity, Respiration, and Light-Response Parameters of World Grassland and Agroecosystems Derived From Flux-Tower Measurements
Gilmanov, T.G. ; Aires, L. ; Barsca, V. ; Baron, S. ; Moors, E.J. ; Jacobs, A. - \ 2010
Rangeland Ecology & Management 63 (2010)1. - ISSN 1550-7424 - p. 16 - 39.
koolstofcyclus - kooldioxide - netto ecosysteem koolstofbalans - graslanden - agro-ecosystemen - meting - carbon cycle - carbon dioxide - net ecosystem carbon balance - grasslands - agroecosystems - measurement - carbon-dioxide exchange - net ecosystem exchange - gross primary productivity - northern great-plains - eddy covariance - co2 exchange - temperate grassland - tallgrass prairie - water-vapor - soil
Grasslands and agroecosystems occupy one-third of the terrestrial area, but their contribution to the global carbon cycle remains uncertain. We used a set of 316 site-years of CO2 exchange measurements to quantify gross primary productivity, respiration, and light-response parameters of grasslands, shrublands/savanna, wetlands, and cropland ecosystems worldwide. We analyzed data from 72 global flux-tower sites partitioned into gross photosynthesis and ecosystem respiration with the use of the light-response method (Gilmanov, T. G., D. A. Johnson, and N. Z. Saliendra. 2003. Growing season CO2 fluxes in a sagebrush-steppe ecosystem in Idaho: Bowen ratio/energy balance measurements and modeling. Basic and Applied Ecology 4:167–183) from the RANGEFLUX and WORLDGRASSAGRIFLUX data sets supplemented by 46 sites from the FLUXNET La Thuile data set partitioned with the use of the temperature-response method (Reichstein, M., E. Falge, D. Baldocchi, D. Papale, R. Valentini, M. Aubinet, P. Berbigier, C. Bernhofer, N. Buchmann, M. Falk, T. Gilmanov, A. Granier, T. Grünwald, K. Havránková, D. Janous, A. Knohl, T. Laurela, A. Lohila, D. Loustau, G. Matteucci, T. Meyers, F. Miglietta, J. M. Ourcival, D. Perrin, J. Pumpanen, S. Rambal, E. Rotenberg, M. Sanz, J. Tenhunen, G. Seufert, F. Vaccari, T. Vesala, and D. Yakir. 2005. On the separation of net ecosystem exchange into assimilation and ecosystem respiration: review and improved algorithm. Global Change Biology 11:1424–1439). Maximum values of the quantum yield (a=75 mmol·mol-1), photosynthetic capacity (Amax=3.4 mg CO2·m-2·s-1), gross photosynthesis (Pg,max=116 g CO2·m-2·d-1), and ecological light-use efficiency (ecol=59 mmol·mol-1) of managed grasslands and high-production croplands exceeded those of most forest ecosystems, indicating the potential of nonforest ecosystems for uptake of atmospheric CO2. Maximum values of gross primary production (8600 g CO2·m-2·yr-1), total ecosystem respiration (7900 g CO2·m-2·yr-1), and net CO2 exchange (2400 g CO2·m-2·yr-1) were observed for intensively managed grasslands and high-yield crops, and are comparable to or higher than those for forest ecosystems, excluding some tropical forests. On average, 80% of the nonforest sites were apparent sinks for atmospheric CO2, with mean net uptake of 700 g CO2·m-2·yr-1 for intensive grasslands and 933 g CO2·m-2·d-1 for croplands. However, part of these apparent sinks is accumulated in crops and forage, which are carbon pools that are harvested, transported, and decomposed off site. Therefore, although agricultural fields may be predominantly sinks for atmospheric CO2, this does not imply that they are necessarily increasing their carbon stock
Comparing observations and process-based simulationsof biosphere-atmosphere exchanges on multiple timescales
Moors, E.J. ; Mahecha, M.D. ; Reichstein, M. ; Jung, M. ; Seneviratne, S.I. ; Zaehle, S. ; Beer, C. ; Braakhekke, M.C. ; Carvalhais, N. ; Lange, H. ; Maire, G. Le - \ 2010
Journal of Geophysical Research: Biogeosciences 115 (2010). - ISSN 2169-8953 - 21 p.
net ecosystem exchange - interannual time scales - global vegetation model - energy-balance closure - eddy covariance - stomatal conductance - climate-change - water-vapor - pine forest - long-term
Terrestrial biosphere models are indispensable tools for analyzing the biosphere-atmosphere exchange of carbon and water. Evaluation of these models using site level observations scrutinizes our current understanding of biospheric responses to meteorological variables. Here we propose a novel model-data comparison strategy considering that CO2 and H2O exchanges fluctuate on a wide range of timescales. Decomposing simulated and observed time series into subsignals allows to quantify model performance as a function of frequency, and to localize model-data disagreement in time. This approach is illustrated using site level predictions from two models of different complexity, Organizing Carbon and Hydrology in Dynamic Ecosystems (ORCHIDEE) and Lund-Potsdam-Jena (LPJ), at four eddy covariance towers in different climates. Frequency-dependent errors reveal substantial model-data disagreement in seasonal-annual and high-frequency net CO2 fluxes. By localizing these errors in time we can trace these back, for example, to overestimations of seasonal-annual periodicities of ecosystem respiration during spring greenup and autumn in both models. In the same frequencies, systematic misrepresentations of CO2 uptake severely affect the performance of LPJ, which is a consequence of the parsimonious representation of phenology. ORCHIDEE shows pronounced model-data disagreements in the high-frequency fluctuations of evapotranspiration across the four sites. We highlight the advantages that our novel methodology offers for a rigorous model evaluation compared to classical model evaluation approaches. We propose that ongoing model development will benefit from considering model-data (dis)agreements in the time-frequency domain
Comparison of chamber and eddy covariance-based CO2 and CH4 emission estimates in a heterogeneous grass ecosystem on peat
Schrier-Uijl, A.P. ; Kroon, P.S. ; Hensen, A. ; Leffelaar, P.A. ; Berendse, F. ; Veenendaal, E.M. - \ 2010
Agricultural and Forest Meteorology 150 (2010)6. - ISSN 0168-1923 - p. 825 - 831.
methaan - kooldioxide - emissie - schattingen - eddy-covariantie - broeikasgassen - veenweiden - methane - carbon dioxide - emission - estimates - eddy covariance - greenhouse gases - peat grasslands - carbon-dioxide exchange - flux measurements - methane emission - nitrous-oxide - water-vapor - spatial variation - soil respiration - polygonal tundra - fen - systems
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
Remote sensing of sun-induced fluorescence to improve modeling of diurnal courses of gross primary production (GPP)
Damm, A. ; Elbers, J.A. ; Erler, A. ; Giolis, B. ; Hamdi, K. ; Hutjes, R.W.A. ; Kosvancova, M. ; Meroni, M. ; Migliettas, F. ; Moersch, A. ; Moreno, J. ; Schickling, A. ; Sonnenschein, R. ; Udelhoven, T. ; Linden, S. van der; Hostert, P. ; Rascher, U. - \ 2010
Global Change Biology 16 (2010)1. - ISSN 1354-1013 - p. 171 - 186.
koolstofcyclus - primaire productie - remote sensing - fluorescentie - spectroscopie - planten - fotosynthese - modelleren - carbon cycle - primary production - remote sensing - fluorescence - spectroscopy - plants - photosynthesis - modeling - light-use efficiency - induced chlorophyll fluorescence - photochemical reflectance index - net primary production - eddy covariance - photosynthetic efficiency - leaf senescence - photosystem-ii - carbon-dioxide - boreal forest
Terrestrial gross primary production (GPP) is an important parameter to explore and quantify carbon fixation by plant ecosystems at various scales. Remote sensing (RS) offers a unique possibility to investigate GPP in a spatially explicit fashion; however, budgeting of terrestrial carbon cycles based on this approach still remains uncertain. To improve calculations, spatio-temporal variability of GPP must be investigated in more detail on local and regional scales. The overarching goal of this study is to enhance our knowledge on how environmentally induced changes of photosynthetic light-use efficiency (LUE) are linked with optical RS parameters. Diurnal courses of sun-induced fluorescence yield (FSyield) and the photochemical reflectance index of corn were derived from high-resolution spectrometric measurements and their potential as proxies for LUE was investigated. GPP was modeled using Monteith's LUE-concept and optical-based GPP and LUE values were compared with synoptically acquired eddy covariance data. It is shown that the diurnal response of complex physiological regulation of photosynthesis can be tracked reliably with the sun-induced fluorescence. Considering structural and physiological effects, this research shows for the first time that including sun-induced fluorescence into modeling approaches improves their results in predicting diurnal courses of GPP. Our results support the hypothesis that air- or spaceborne quantification of sun-induced fluorescence yield may become a powerful tool to better understand spatio-temporal variations of fluorescence yield, photosynthetic efficiency and plant stress on a global scale
Eddy covariance observations of CH4 and N2O : towards more accurate emission estimates
Schrier-Uijl, Arina - \ 2009
methane - nitrous oxide - emission - estimates - eddy covariance - meteorological observations
Eddy covariance observations of CH4 and N2O : Towards more accurate emission estimates
Kroon, P. ; Hensen, A. ; Jonker, H. ; Schrier-Uijl, A.P. ; Bosveld, F. - \ 2009
methaan - distikstofmonoxide - eddy-covariantie - meteorologische waarnemingen - emissie - schattingen - methane - nitrous oxide - eddy covariance - meteorological observations - emission - estimates
Poster presentation at the Early Career Scientist Workshop, 20 – 22 August 2009, Melbourne Australia.
Sensible and latent heat flux from radiometric surface temperatures at the regional scale: methodology and validation
Miglietta, F. ; Gioli, B. ; Brunet, Y. ; Hutjes, R.W.A. ; Matese, A. ; Sarrat, C. ; Zaldei, A. - \ 2009
Biogeosciences 6 (2009). - ISSN 1726-4170 - p. 1975 - 1986.
klimaatverandering - kooldioxide - temperatuur - modellen - climatic change - carbon dioxide - temperature - models - convective boundary-layer - evapotranspiration rates - eddy covariance - carbon-dioxide - water-vapor - aircraft - model - airborne - field - emissivity
The CarboEurope Regional Experiment Strategy (CERES) was designed to develop and test a range of methodologies to assess regional surface energy and mass exchange of a large study area in the south-western part of France. This paper describes a methodology to estimate sensible and latent heat fluxes on the basis of net radiation, surface radiometric temperature measurements and information obtained from available products derived from the Meteosat Second Generation (MSG) geostationary meteorological satellite, weather stations and ground-based eddy covariance towers. It is based on a simplified bulk formulation of sensible heat flux that considers the degree of coupling between the vegetation and the atmosphere and estimates latent heat as the residual term of net radiation. Estimates of regional energy fluxes obtained in this way are validated at the regional scale by means of a comparison with direct flux measurements made by airborne eddy-covariance. The results show an overall good matching between airborne fluxes and estimates of sensible and latent heat flux obtained from radiometric surface temperatures that holds for different weather conditions and different land use types. The overall applicability of the proposed methodology to regional studies is discussed
Latitudinal patterns of magnitude and interannual variability in net ecosystem exchange regulated by biological and environmental variables
Yuan, W.P. ; Luo, Y.Q. ; Richardson, A.D. ; Oren, R. ; Luyssaert, S. ; Janssens, I.A. ; Ceulemans, R. ; Zhou, X.H. ; Grunwald, T. ; Aubinet, M. ; Berhofer, C. ; Baldocchi, D.D. ; Chen, J.Q. ; Dunn, A.L. ; Deforest, J.L. ; Dragoni, D. ; Goldstein, A.H. ; Moors, E.J. ; Munger, J.W. ; Monson, R.K. ; Suyker, A.E. ; Star, G. ; Scott, R.L. ; Tenhunen, J. ; Verma, S.B. ; Vesala, T. ; Wofsy, S. - \ 2009
Global Change Biology 15 (2009)12. - ISSN 1354-1013 - p. 2905 - 2920.
netto ecosysteem uitwisseling - kooldioxide - eddy-covariantie - patronen - ruimtelijke variatie - variatie in de tijd - net ecosystem exchange - carbon dioxide - eddy covariance - patterns - spatial variation - temporal variation - water-vapor exchange - northern temperate grassland - native tallgrass prairie - carbon-dioxide exchange - long-term measurements - plant functional-type - eddy covariance data - deciduous forest - european forests - co2 exchange
Over the last two and half decades, strong evidence showed that the terrestrial ecosystems are acting as a net sink for atmospheric carbon. However the spatial and temporal patterns of variation in the sink are not well known. In this study, we examined latitudinal patterns of interannual variability (IAV) in net ecosystem exchange (NEE) of CO2 based on 163 site-years of eddy covariance data, from 39 northern-hemisphere research sites located at latitudes ranging from ~29°N to ~64°N. We computed the standard deviation of annual NEE integrals at individual sites to represent absolute interannual variability (AIAV), and the corresponding coefficient of variation as a measure of relative interannual variability (RIAV). Our results showed decreased trends of annual NEE with increasing latitude for both deciduous broadleaf forests and evergreen needleleaf forests. Gross primary production (GPP) explained a significant proportion of the spatial variation of NEE across evergreen needleleaf forests, whereas, across deciduous broadleaf forests, it is ecosystem respiration (Re). In addition, AIAV in GPP and Re increased significantly with latitude in deciduous broadleaf forests, but AIAV in GPP decreased significantly with latitude in evergreen needleleaf forests. Furthermore, RIAV in NEE, GPP, and Re appeared to increase significantly with latitude in deciduous broadleaf forests, but not in evergreen needleleaf forests. Correlation analyses showed air temperature was the primary environmental factor that determined RIAV of NEE in deciduous broadleaf forest across the North American sites, and none of the chosen climatic factors could explain RIAV of NEE in evergreen needleleaf forests. Mean annual NEE significantly increased with latitude in grasslands. Precipitation was dominant environmental factor for the spatial variation of magnitude and IAV in GPP and Re in grasslands.
Temporal and among-site variability of inherent water use efficiency at the ecosystem level
Beer, C. ; Ciais, P. ; Reichstein, M. ; Baldocchi, D. ; Law, B.E. ; Papale, D. ; Soussana, J.F. ; Ammann, C. ; Buchmann, N. ; Frank, D. ; Gianelle, D. ; Janssens, I.A. ; Knohl, A. ; Kostner, B. ; Moors, E.J. ; Roupsard, O. ; Verbeeck, H. ; Vesala, T. ; Williams, C.A. ; Wohlfahrt, G. - \ 2009
Global Biogeochemical Cycles 23 (2009). - ISSN 0886-6236 - 13
watergebruiksrendement - kooldioxide - waterdampbeweging - terrestrische ecosystemen - atmosfeer - koolstofcyclus - water use efficiency - carbon dioxide - water vapour movement - terrestrial ecosystems - atmosphere - carbon cycle - scots pine forest - co2 exchange - carbon-dioxide - eddy covariance - central germany - ponderosa pine - canopy-scale - aspen forest - beech forest - time scales
Half-hourly measurements of the net exchanges of carbon dioxide and water vapor between terrestrial ecosystems and the atmosphere provide estimates of gross primary production (GPP) and evapotranspiration (ET) at the ecosystem level and on daily to annual timescales. The ratio of these quantities represents ecosystem water use efficiency. Its multiplication with mean daylight vapor pressure deficit (VPD) leads to a quantity which we call “inherent water use efficiency” (IWUE*). The dependence of IWUE* on environmental conditions indicates possible adaptive adjustment of ecosystem physiology in response to a changing environment. IWUE* is analyzed for 43 sites across a range of plant functional types and climatic conditions. IWUE* increases during short-term moderate drought conditions. Mean annual IWUE* varied by a factor of 3 among all sites. This is partly explained by soil moisture at field capacity, particularly in deciduous broad-leaved forests. Canopy light interception sets the upper limits to canopy photosynthesis, and explains half the variance in annual IWUE* among herbaceous ecosystems and evergreen needle-leaved forests. Knowledge of IWUE* offers valuable improvement to the representation of carbon and water coupling in ecosystem process models