Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Nutrimetabolomics: An Integrative Action for Metabolomic Analyses in Human Nutritional Studies
Ulaszewska, Marynka M. ; Weinert, Christoph H. ; Trimigno, Alessia ; Portmann, Reto ; Andres Lacueva, Cristina ; Badertscher, René ; Brennan, Lorraine ; Brunius, Carl ; Bub, Achim ; Capozzi, Francesco ; Cialiè Rosso, Marta ; Cordero, Chiara E. ; Daniel, Hannelore ; Durand, Stéphanie ; Egert, Bjoern ; Ferrario, Paola G. ; Feskens, Edith J.M. ; Franceschi, Pietro ; Garcia-Aloy, Mar ; Giacomoni, Franck ; Giesbertz, Pieter ; González-Domínguez, Raúl ; Hanhineva, Kati ; Hemeryck, Lieselot Y. ; Kopka, Joachim ; Kulling, Sabine E. ; Llorach, Rafael ; Manach, Claudine ; Mattivi, Fulvio ; Migné, Carole ; Münger, Linda H. ; Ott, Beate ; Picone, Gianfranco ; Pimentel, Grégory ; Pujos-Guillot, Estelle ; Riccadonna, Samantha ; Rist, Manuela J. ; Rombouts, Caroline ; Rubert, Josep ; Skurk, Thomas ; Sri Harsha, Pedapati S.C. ; Meulebroek, Lieven Van; Vanhaecke, Lynn ; Vázquez-Fresno, Rosa ; Wishart, David ; Vergères, Guy - \ 2018
Molecular Nutrition & Food Research 63 (2018)1. - ISSN 1613-4125
GC–MS - LC–MS - metabolomics - NMR - nutrition
The life sciences are currently being transformed by an unprecedented wave of developments in molecular analysis, which include important advances in instrumental analysis as well as biocomputing. In light of the central role played by metabolism in nutrition, metabolomics is rapidly being established as a key analytical tool in human nutritional studies. Consequently, an increasing number of nutritionists integrate metabolomics into their study designs. Within this dynamic landscape, the potential of nutritional metabolomics (nutrimetabolomics) to be translated into a science, which can impact on health policies, still needs to be realized. A key element to reach this goal is the ability of the research community to join, to collectively make the best use of the potential offered by nutritional metabolomics. This article, therefore, provides a methodological description of nutritional metabolomics that reflects on the state-of-the-art techniques used in the laboratories of the Food Biomarker Alliance (funded by the European Joint Programming Initiative “A Healthy Diet for a Healthy Life” (JPI HDHL)) as well as points of reflections to harmonize this field. It is not intended to be exhaustive but rather to present a pragmatic guidance on metabolomic methodologies, providing readers with useful “tips and tricks” along the analytical workflow.
Atmospheric deposition, CO2, and change in the land carbon sink
Fernández-Martínez, M. ; Vicca, S. ; Janssens, I.A. ; Ciais, P. ; Obersteiner, M. ; Bartrons, M. ; Sardans, Jordi ; Verger, Aleixandre ; Canadell, J.G. ; Chevallier, F. ; Wang, X. ; Bernhofer, C. ; Curtis, P.S. ; Gianelle, D. ; Grünwald, T. ; Heinesch, B. ; Ibrom, A. ; Knohl, A. ; Laurila, T. ; Law, Beverly E. ; Limousin, J.M. ; Longdoz, B. ; Loustau, D. ; Mammarella, I. ; Matteucci, G. ; Monson, R.K. ; Montagnani, L. ; Moors, E.J. ; Munger, J.W. ; Papale, D. ; Piao, S.L. ; Peñuelas, J. - \ 2017
Scientific Reports 7 (2017). - ISSN 2045-2322 - 13 p.

Concentrations of atmospheric carbon dioxide (CO2) have continued to increase whereas atmospheric deposition of sulphur and nitrogen has declined in Europe and the USA during recent decades. Using time series of flux observations from 23 forests distributed throughout Europe and the USA, and generalised mixed models, we found that forest-level net ecosystem production and gross primary production have increased by 1% annually from 1995 to 2011. Statistical models indicated that increasing atmospheric CO2 was the most important factor driving the increasing strength of carbon sinks in these forests. We also found that the reduction of sulphur deposition in Europe and the USA lead to higher recovery in ecosystem respiration than in gross primary production, thus limiting the increase of carbon sequestration. By contrast, trends in climate and nitrogen deposition did not significantly contribute to changing carbon fluxes during the studied period. Our findings support the hypothesis of a general CO2-fertilization effect on vegetation growth and suggest that, so far unknown, sulphur deposition plays a significant role in the carbon balance of forests in industrialized regions. Our results show the need to include the effects of changing atmospheric composition, beyond CO2, to assess future dynamics of carbon-climate feedbacks not currently considered in earth system/climate modelling.

Canopy-scale biophysical controls of transpiration and evaporation in the Amazon Basin
Mallick, Kaniska ; Trebs, Ivonne ; Boegh, Eva ; Giustarini, Laura ; Schlerf, Martin ; Drewry, Darren T. ; Hoffmann, Lucien ; Randow, Celso Von; Kruijt, Bart ; Araùjo, Alessandro ; Saleska, Scott ; Ehleringer, James R. ; Domingues, Tomas F. ; Ometto, Jean Pierre H.B. ; Nobre, Antonio D. ; Luiz Leal De Moraes, Osvaldo ; Hayek, Matthew ; William Munger, J. ; Wofsy, Steven C. - \ 2016
Hydrology and Earth System Sciences 20 (2016)10. - ISSN 1027-5606 - p. 4237 - 4264.

Canopy and aerodynamic conductances (gC and gA) are two of the key land surface biophysical variables that control the land surface response of land surface schemes in climate models. Their representation is crucial for predicting transpiration (λET) and evaporation (λEE) flux components of the terrestrial latent heat flux (λE), which has important implications for global climate change and water resource management. By physical integration of radiometric surface temperature (TR) into an integrated framework of the Penman-Monteith and Shuttleworth-Wallace models, we present a novel approach to directly quantify the canopy-scale biophysical controls on λET and λEE over multiple plant functional types (PFTs) in the Amazon Basin. Combining data from six LBA (Large-scale Biosphere-Atmosphere Experiment in Amazonia) eddy covariance tower sites and a TR-driven physically based modeling approach, we identified the canopy-scale feedback-response mechanism between gC, λET, and atmospheric vapor pressure deficit (DA), without using any leaf-scale empirical parameterizations for the modeling. The TR-based model shows minor biophysical control on λET during the wet (rainy) seasons where λET becomes predominantly radiation driven and net radiation (RN) determines 75 to 80% of the variances of λET. However, biophysical control on λET is dramatically increased during the dry seasons, and particularly the 2005 drought year, explaining 50 to 65% of the variances of λET, and indicates λET to be substantially soil moisture driven during the rainfall deficit phase. Despite substantial differences in gA between forests and pastures, very similar canopy-atmosphere "coupling" was found in these two biomes due to soil moisture-induced decrease in gC in the pasture. This revealed the pragmatic aspect of the TR-driven model behavior that exhibits a high sensitivity of gC to per unit change in wetness as opposed to gA that is marginally sensitive to surface wetness variability. Our results reveal the occurrence of a significant hysteresis between λET and gC during the dry season for the pasture sites, which is attributed to relatively low soil water availability as compared to the rainforests, likely due to differences in rooting depth between the two systems. Evaporation was significantly influenced by gA for all the PFTs and across all wetness conditions. Our analytical framework logically captures the responses of gC and gA to changes in atmospheric radiation, DA, and surface radiometric temperature, and thus appears to be promising for the improvement of existing land-surface-atmosphere exchange parameterizations across a range of spatial scales.

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.
Toward a consistency cross-check of eddy covariance flux-based and biometric estimates of ecosystem carbon balance
Luyssaert, S. ; Reichstein, M. ; Schulze, E.D. ; Janssens, I.A. ; Law, B.E. ; Papale, D. ; Dragoni, D. ; Goulden, M.L. ; Granier, A. ; Kutch, W.L. ; Linder, S. ; Matteucci, G. ; Moors, E.J. ; Munger, J.W. ; Pilegaard, K. ; Saunders, M. ; Falge, E.M. - \ 2009
Global Biogeochemical Cycles 23 (2009). - ISSN 0886-6236 - 13
netto ecosysteem koolstofbalans - schattingen - eddy-covariantie - primaire productie - biometrie - meetsystemen - net ecosystem carbon balance - estimates - eddy covariance - primary production - biometry - measurement systems - net primary production - gross primary production - ponderosa pine forests - mixed hardwood forest - water-vapor exchange - soil co2 efflux - european forests - beech forest - chamber measurements - spatial variability
Quantification of an ecosystem's carbon balance and its components is pivotal for understanding both ecosystem functioning and global cycling. Several methods are being applied in parallel to estimate the different components of the CO2 balance. However, different methods are subject to different sources of error. Therefore, it is necessary that site level component estimates are cross-checked against each other before being reported. Here we present a two-step approach for testing the accuracy and consistency of eddy covariance–based gross primary production (GPP) and ecosystem respiration (Re) estimates with biometric measurements of net primary production (NPP), autotrophic (Ra) and heterotrophic (Rh) respiration. The test starts with closing the CO2 balance to account for reasonable errors in each of the component fluxes. Failure to do so within the constraints will classify the flux estimates on the site level as inconsistent. If the CO2 balance can be closed, the test continues by comparing the closed site level Ra/GPP with the Rh/GPP ratio. The consistency of these ratios is then judged against expert knowledge. Flux estimates of sites that pass both steps are considered consistent. An inconsistent ratio is not necessarily incorrect but provides a signal for careful data screening that may require further analysis to identify the possible biological reasons of the unexpected ratios. We reviewed the literature and found 16 sites, out of a total of 529 research forest sites, that met the data requirements for the consistency test. Thirteen of these sites passed both steps of the consistency cross-check. Subsequently, flux ratios (NPP/GPP, Rh/NPP, Rh/Re, and Re/GPP) were calculated for the consistent sites. Similar ratios were observed at sites which lacked information to check consistency, indicating that the flux data that are currently used for validating models and testing ecological hypotheses are largely consistent across a wide range of site productivities. Confidence in the output of flux networks could be further enhanced if the required fluxes are independently estimated at all sites for multiple years and harmonized methods are used
Estimating noctural ecosystem respiration from the vertical turbulent flux and change in storange of CO2
Gorsel, E. van; Delpierre, N. ; Leuning, R. ; Black, A. ; Munger, J.W. ; Wofsy, S. ; Aubinet, M. ; Feigenwinter, C. ; Beringer, J. ; Bonal, D. ; Chen, B. ; Chen, J. ; Clement, R. ; Davis, K.J. ; Desai, A.R. ; Dragoni, D. ; Etzold, S. ; Grünwald, T. ; Gu, L. ; Heinesch, B. ; Hutyra, L.R. ; Jans, W.W.P. ; Kutsch, W. ; Law, B.E. ; Leclerc, Y. ; Mammarella, I. ; Montagnani, L. ; Noormets, A. ; Rebmann, C. ; Wharton, S. - \ 2009
Agricultural and Forest Meteorology 149 (2009)11. - ISSN 0168-1923 - p. 1919 - 1930.
ecosystemen - ademhaling - meettechnieken - nacht - kooldioxide - eddy-covariantie - micrometeorologie - luchtstroming - netto ecosysteem koolstofbalans - ecosystems - respiration - measurement techniques - night - carbon dioxide - eddy covariance - micrometeorology - air flow - net ecosystem carbon balance - eddy covariance measurements - temperate deciduous forest - carbon-dioxide exchange - ponderosa pine forests - long-term measurements - douglas-fir stand - old-growth forest - soil respiration - pacific-northwest - difficult conditions
Micrometeorological measurements of nighttime ecosystem respiration can be systematically biased when stable atmospheric conditions lead to drainage flows associated with decoupling of air flow above and within plant canopies. The associated horizontal and vertical advective fluxes cannot be measured using instrumentation on the single towers typically used at micrometeorological sites. A common approach to minimize bias is to use a threshold in friction velocity, u*, to exclude periods when advection is assumed to be important, but this is problematic in situations when in-canopy flows are decoupled from the flow above. Using data from 25 flux stations in a wide variety of forest ecosystems globally, we examine the generality of a novel approach to estimating nocturnal respiration developed by van Gorsel et al. (van Gorsel, E., Leuning, R., Cleugh, H.A., Keith, H., Suni, T., 2007. Nocturnal carbon efflux: reconciliation of eddy covariance and chamber measurements using an alternative to the u*-threshold filtering technique. Tellus 59B, 397–403, Tellus, 59B, 307-403). The approach is based on the assumption that advection is small relative to the vertical turbulent flux (FC) and change in storage (FS) of CO2 in the few hours after sundown. The sum of FC and FS reach a maximum during this period which is used to derive a temperature response function for ecosystem respiration. Measured hourly soil temperatures are then used with this function to estimate respiration RRmax. The new approach yielded excellent agreement with (1) independent measurements using respiration chambers, (2) with estimates using ecosystem light-response curves of Fc + Fs extrapolated to zero light, RLRC, and (3) with a detailed process-based forest ecosystem model, Rcast. At most sites respiration rates estimated using the u*-filter, Rust, were smaller than RRmax and RLRC. Agreement of our approach with independent measurements indicates that RRmax provides an excellent estimate of nighttime ecosystem respiration.
CO2 balance of boreal, temperate, and tropical forests
Luyssaert, S. ; Inglima, I. ; Jungs, M. ; Richardson, A. ; Reichsteins, M. ; Papale, D. ; Piao, S.L. ; Schulzes, E.D. ; Wingate, L. ; Matteucci, G. ; Aragaoss, L. ; Aubinet, M. ; Beers, C. van; Bernhofer, C. ; Black, K.G. ; Bonal, D. ; Bonnefonds, J.M. ; Chambers, J. ; Ciais, P. ; Cook, B. ; Davis, K.J. ; Dolman, A.J. ; Gielen, B. ; Goulden, M. ; Grace, J. ; Granier, A. ; Grelle, A. ; Griffis, T. ; Grunwald, T. ; Guidolotti, G. ; Hanson, P.J. ; Harding, R. ; Hollinger, D.Y. ; Hutyra, L.R. ; Kolari, P. ; Kruijt, B. ; Kutsch, W. ; Lagergren, F. ; Laurila, T. ; Law, B.E. ; Maire, G. Le; Lindroth, A. ; Loustau, D. ; Malhi, Y. ; Mateus, J. ; Migliavacca, M. ; Misson, L. ; Montagnani, L. ; Moncrief, J. ; Moors, E.J. ; Munger, J.W. ; Nikinmaa, E. ; Ollinger, S.V. ; Pita, G. ; Rebmann, C. ; Roupsard, O. ; Saigusa, N. ; Sanz, M.J. ; Seufert, G. ; Sierra, C. ; Smith, M. ; Tang, J. ; Valentini, R. ; Vesala, T. ; Janssens, I.A. - \ 2007
Global Change Biology 13 (2007)12. - ISSN 1354-1013 - p. 2509 - 2537.
net primary production - carbon-dioxide exchange - total soil respiration - eddy-covariance measurements - water-vapor exchange - black spruce forests - ponderosa pine forests - amazonian rain-forest - broad-leaved forest - gross primary production
Terrestrial ecosystems sequester 2.1 Pg of atmospheric carbon annually. A large amount of the terrestrial sink is realized by forests. However, considerable uncertainties remain regarding the fate of this carbon over both short and long timescales. Relevant data to address these uncertainties are being collected at many sites around the world, but syntheses of these data are still sparse. To facilitate future synthesis activities, we have assembled a comprehensive global database for forest ecosystems, which includes carbon budget variables (fluxes and stocks), ecosystem traits (e.g. leaf area index, age), as well as ancillary site information such as management regime, climate, and soil characteristics. This publicly available database can be used to quantify global, regional or biome-specific carbon budgets; to re-examine established relationships; to test emerging hypotheses about ecosystem functioning [e.g. a constant net ecosystem production (NEP) to gross primary production (GPP) ratio]; and as benchmarks for model evaluations. In this paper, we present the first analysis of this database. We discuss the climatic influences on GPP, net primary production (NPP) and NEP and present the CO2 balances for boreal, temperate, and tropical forest biomes based on micrometeorological, ecophysiological, and biometric flux and inventory estimates. Globally, GPP of forests benefited from higher temperatures and precipitation whereas NPP saturated above either a threshold of 1500 mm precipitation or a mean annual temperature of 10 °C. The global pattern in NEP was insensitive to climate and is hypothesized to be mainly determined by nonclimatic conditions such as successional stage, management, site history, and site disturbance. In all biomes, closing the CO2 balance required the introduction of substantial biome-specific closure terms. Nonclosure was taken as an indication that respiratory processes, advection, and non-CO2 carbon fluxes are not presently being adequately accounted for.
Environmental controls over carbon dioxide and water vapor exchange of terrestrial vegetation
Law, B.E. ; Falge, E. ; Gu, L. ; Baldocchi, D.D. ; Bakwin, P. ; Berbigier, P. ; Davis, K. ; Dolman, A.J. ; Falk, M. ; Fuentes, J.D. ; Goldstein, A. ; Granier, A. ; Hollinger, D. ; Janssens, I.A. ; Jarvis, P. ; Jensen, N.O. ; Katul, G. ; Mahli, Y. ; Matteucci, G. ; Meyers, T. ; Monson, R. ; Munger, W. ; Oechel, W. ; Olson, R. ; Pilegaard, K. ; Paw U, K.T. ; Thorgeirsson, H. ; Valentini, R. ; Verma, S. - \ 2002
Agricultural and Forest Meteorology 113 (2002)1-4. - ISSN 0168-1923 - p. 97 - 120.
broeikaseffect - ecologie - klimaat - koolstofhuishouding - meteorologie - vegetatie - verdamping - waterhuishouding
Phase and amplitude of ecosystem carbon release and uptake potentials as derived from FLUXNET measurements
Falge, E. ; Tenhunen, J. ; Baldocchi, D. ; Aubinet, M. ; Bakwin, P. ; Berbigier, P. ; Bernhofer, C. ; Bonnefond, J.M. ; Burba, G. ; Clement, R. ; Davis, K.J. ; Elbers, J.A. ; Falk, M. ; Goldstein, A.H. ; Grelle, A. ; Granier, A. ; Grünwald, T. ; Gudmundsson, J. ; Hollinger, D. ; Janssens, I.A. ; Keronen, P. ; Kowalski, A.S. ; Katul, G. ; Law, B.E. ; Malhi, Y. ; Meyers, T. ; Monson, R.K. ; Moors, E.J. ; Munger, J.W. - \ 2002
Agricultural and Forest Meteorology 113 (2002)1-4. - ISSN 0168-1923 - p. 75 - 95.
bos - broeikaseffect - ecologie - energiebalans - klimaat - koolstofhuishouding - meteorologie - vegetatie
Seasonality of ecosystem respiration and gross primary production as derived from FLUXNET measurements
Falge, E. ; Baldocchi, D. ; Tenhunen, J. ; Aubinet, M. ; Bakwin, P. ; Berbigier, P. ; Bernhofer, C. ; Burba, G. ; Clement, R. ; Davis, K.J. ; Elbers, J.A. ; Goldstein, A. ; Grelle, A. ; Granier, A. ; Gudmundsson, J. ; Hollinger, D. ; Kowalski, A.S. ; Katul, G. ; Law, B.E. ; Malhi, Y. ; Meyers, T. ; Monson, R.K. ; Munger, J.W. ; Oechel, W. ; Paw U, K.T. ; Pilegaard, K. ; Rannik, Ü. ; Rebmann, C. ; Suyker, A. - \ 2002
Agricultural and Forest Meteorology 113 (2002)1-4. - ISSN 0168-1923 - p. 53 - 74.
bos - broeikaseffect - ecologie - energiebalans - klimaat - meteorologie - koolstofhuishouding - vegetatie - verdamping
Gap filling strategies for long term energy flux data sets
Falge, E. ; Baldocchi, D. ; Olson, R. ; Anthoni, P. ; Aubinet, M. ; Bernhofer, C. ; Burba, G. ; Ceulemans, R. ; Clement, R. ; Dolman, H. ; Granier, A. ; Gross, P. ; Grünwald, T. ; Hollinger, D. ; Jensen, N.O. ; Katul, G. ; Keronen, P. ; Kowalski, A. ; Lai, C.T. ; Law, B.E. ; Meyers, T. ; Moncrieff, J. ; Moors, E.J. ; Munger, J.W. ; Pilegaard, K. ; Rebmann, C. ; Suyker, A. ; Tenhunen, J. ; Tu, K. - \ 2001
Agricultural and Forest Meteorology 107 (2001)1. - ISSN 0168-1923 - p. 71 - 77.
At present a network of over 100 field sites are measuring carbon dioxide, water vapor and sensible heat fluxes between the biosphere and atmosphere, on a nearly continuous basis. Gaps in the long term measurements of evaporation and sensible heat flux must be filled before these data can be used for hydrological and meteorological applications. We adapted methods of gap filling for NEE (net ecosystem exchange of carbon) to energy fluxes and applied them to data sets available from the EUROFLUX and AmeriFlux eddy covariance databases. The average data coverage for the sites selected was 69% and 75% for latent heat (λE) and sensible heat (H). The methods were based on mean diurnal variations (half-hourly binned means of fluxes based on previous and subsequent days, MDV) and look-up tables for fluxes during assorted meteorological conditions (LookUp), and the impact of different gap filling methods on the annual sum of λE and H is investigated. The difference between annual λE filled by MDV and λE filled by LookUp ranged from - 120 to 210 MJ m-2 per year, i.e. -48 to +86 mm per year, or -13 to +39% of the annual sum. For annual sums of H differences between -140 and + 140 MJ m-2 per year or -12 to +19% of the annual sum were found.
Gap filling strategies for defensible annual sums of net ecosystem exchange
Falge, E. ; Baldocchi, D. ; Olson, R. ; Anthoni, P. ; Aubinet, M. ; Bernhofer, C. ; Burba, G. ; Ceulemans, R. ; Clement, R. ; Dolman, H. ; Granier, A. ; Gross, P. ; Grünwald, T. ; Hollinger, D. ; Jensen, N.O. ; Katul, G. ; Keronen, P. ; Kowalski, A. ; Lai, C.T. ; Law, B.E. ; Meyers, T. ; Moncrieff, J. ; Moors, E.J. ; Munger, J.W. ; Pilegaard, K. ; Rebmann, C. ; Suyker, A. ; Tenhunen, J. ; Tu, K. - \ 2001
Agricultural and Forest Meteorology 107 (2001)1. - ISSN 0168-1923 - p. 43 - 69.
Heightened awareness of global change issues within both science and political communities has increased interest in using the global network of eddy covariance flux towers to more fully understand the impacts of natural and anthropogenic phenomena on the global carbon balance. Comparisons of net ecosystem exchange (FNEE) responses are being made among biome types, phenology patterns, and stress conditions. The comparisons are usually performed on annual sums of FNEE; however, the average data coverage during a year is only 65%. Therefore, robust and consistent gap filling methods are required. We review several methods of gap filling and apply them to data sets available from the EUROFLUX and AmeriFlux databases. The methods are based on mean diurnal variation (MDV), look-up tables (LookUp), and nonlinear regressions (Regr.), and the impact of different gap filling methods on the annual sum of FNEE is investigated. The difference between annual FNEE filled by MDV compared to FNEE filled by Regr. ranged from -45 to +200 g C m-2 per year (MDV-Regr.). Comparing LookUp and Regr. methods resulted in a difference (LookUp-Regr.) ranging from -30 to +150 g C m-2 per year. We also investigated the impact of replacing measurements at night, when turbulent mixing is insufficient. The nighttime correction for low friction velocities (u*) shifted annual FNEE on average by +77 g C m-2 per year, but in certain cases as much as + 185 g C m-2 per year. Our results emphasize the need to standardize gap filling-methods for improving the comparability of flux data products from regional and global flux networks.
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