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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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.

Evaluating the performance of commonly used gas analysers for methane eddy covariance flux measurements: the InGOS inter-comparison field experiment
Peltola, O. ; Hensen, A. ; Helfter, C. ; Belelli Marchesini, L. ; Bosveld, F.C. ; Bulk, W.C.M. van de; Elbers, J.A. ; Haapanala, S. ; Holst, J. ; Laurila, T. ; Lindroth, A. ; Nemitz, E. ; Röckmann, T. ; Vermeulen, A.T. ; Mammarella, I. - \ 2014
Biogeosciences 11 (2014). - ISSN 1726-4170 - p. 3163 - 3186.
water-vapor - atmospheric methane - mixing-ratio - wpl terms - path - ch4 - attenuation - accuracy - strategy - quality
The performance of eight fast-response methane (CH4) gas analysers suitable for eddy covariance flux measurements were tested at a grassland site near the Cabauw tall tower (Netherlands) during June 2012. The instruments were positioned close to each other in order to minimise the effect of varying turbulent conditions. The moderate CH4 fluxes observed at the location, of the order of 25 nmol m-2 s-1, provided a suitable signal for testing the instruments' performance. Generally, all analysers tested were able to quantify the concentration fluctuations at the frequency range relevant for turbulent exchange and were able to deliver high-quality data. The tested cavity ringdown spectrometer (CRDS) instruments from Picarro, models G2311-f and G1301-f, were superior to other CH4 analysers with respect to instrumental noise. As an open-path instrument susceptible to the effects of rain, the LI-COR LI-7700 achieved lower data coverage and also required larger density corrections; however, the system is especially useful for remote sites that are restricted in power availability. In this study the open-path LI-7700 results were compromised due to a data acquisition problem in our data-logging setup. Some of the older closed-path analysers tested do not measure H2O concentrations alongside CH4 (i.e. FMA1 and DLT-100 by Los Gatos Research) and this complicates data processing since the required corrections for dilution and spectroscopic interactions have to be based on external information. To overcome this issue, we used H2O mole fractions measured by other gas analysers, adjusted them with different methods and then applied them to correct the CH4 fluxes. Following this procedure we estimated a bias of the order of 0.1 g (CH4) m-2 (8% of the measured mean flux) in the processed and corrected CH4 fluxes on a monthly scale due to missing H2O concentration measurements. Finally, cumulative CH4 fluxes over 14 days from three closed-path gas analysers, G2311-f (Picarro Inc.), FGGA (Los Gatos Research) and FMA2 (Los Gatos Research), which were measuring H2O concentrations in addition to CH4, agreed within 3% (355–367 mg (CH4) m-2) and were not clearly different from each other, whereas the other instruments derived total fluxes which showed small but distinct differences (±10%, 330–399 mg (CH4) m-2).
Quality control of CarboEurope flux data - Part 1: Coupling footprint analyses with flux data quality assessment to evaluate sites in forest ecosystems
Gockede, M. ; Foken, T. ; Aubinet, M. ; Aurela, M. ; Banza, J. ; Bernhofer, C. ; Bonnefonds, J.M. ; Brunet, Y. ; Carrara, A. ; Clement, R. ; Dellwik, E. ; Elbers, J.A. ; Eugster, W. ; Fuhrer, J. ; Granier, A. ; Grunwald, T. ; Heinsch, B. ; Janssens, I.A. ; Knohl, A. ; Koeble, R. ; Laurila, T. ; Longdoz, B. ; Manca, G. ; Marek, M. ; Markkanen, T. ; Mateus, J. ; Matteucci, G. ; Mauder, M. ; Migliavacca, M. ; Minerbi, S. ; Moncrieff, J. ; Montagnani, L. ; Moors, E.J. ; Ourcival, J.M. ; Papale, D. ; Pereira, J.M. ; Pilegaard, K. ; Pita, G. ; Rambal, S. ; Rebmann, C. ; Rodrigues, A. ; Rotenberg, E. ; Sanz, M.J. ; Sedlak, P. ; Seufert, G. ; Siebicke, L. ; Soussana, J.F. ; Valentini, R. ; Vesala, T. ; Verbeeck, H. ; Yakir, D. - \ 2008
Biogeosciences 5 (2008)2. - ISSN 1726-4170 - p. 433 - 450.
warmtestroming - eddy-covariantie - gegevensanalyse - ecosystemen - bossen - atmosferische grenslaag - heat flow - eddy covariance - data analysis - ecosystems - forests - atmospheric boundary-layer - eddy covariance measurements - water-vapor - boundary-layer - heat-flux - turbulence statistics - correlation systems - stochastic-models - sonic anemometer - surface fluxes - carbon-dioxide
We applied a site evaluation approach combining Lagrangian Stochastic footprint modeling with a quality assessment approach for eddy-covariance data to 25 forested sites of the CarboEurope-IP network. The analysis addresses the spatial representativeness of the flux measurements, instrumental effects on data quality, spatial patterns in the data quality, and the performance of the coordinate rotation method. Our findings demonstrate that application of a footprint filter could strengthen the CarboEurope-IP flux database, since only one third of the sites is situated in truly homogeneous terrain. Almost half of the sites experience a significant reduction in eddy-covariance data quality under certain conditions, though these effects are mostly constricted to a small portion of the dataset. Reductions in data quality of the sensible heat flux are mostly induced by characteristics of the surrounding terrain, while the latent heat flux is subject to instrumentation-related problems. The Planar-Fit coordinate rotation proved to be a reliable tool for the majority of the sites using only a single set of rotation angles. Overall, we found a high average data quality for the CarboEurope-IP network, with good representativeness of the measurement data for the specified target land cover types.
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.
EU peatlands: An overview of current trace gas fluxes
Drösler, M. ; Freibauer, A. ; Veenendaal, E.M. ; Christensen, T. ; Friborg, Th. ; Andersen-Dunn, M. ; Aurela, M. ; Byrne, K. ; Bergmann, L. ; Chojnicki, B. ; Hendricks, D. ; Jungkunst, H. ; Laurila, T. ; Llyod, C. ; Lund, M. ; Nilsson, M. ; Olejnik, J. ; Rinne, J. ; Riutta, T. ; Schrier-Uijl, A.P. - \ 2007
In: Proceedings of the First International Symposium on Carbon in Peatlands, Wageningen, The Netherlands, 15 - 18 April 2007. - Wageningen : Wageningen University - p. 36 - 36.
Partitioning European grassland net ecosystem CO2 exchange into grass primary productivity and ecosystem respiration using response function analysis
Gilmanov, T.G. ; Soussana, J.F. ; Aires, A. ; Allard, V. ; Ammann, C. ; Balzarolo, M. ; Barcza, C. ; Bernhofer, C. ; Campbell, C.L. ; Cernusca, A. ; Cescatti, A. ; Clifton-Brown, J.C. ; Dirks, B.O.M. ; Dore, S. ; Eugster, W. ; Fuhrer, J. ; Gimeno, C. ; Gruenwald, T. ; Haszpra, L. ; Hensen, A. ; Ibrom, A. ; Jacobs, A.F.G. ; Jones, M.B. ; Lanigan, G. ; Laurila, T. ; Lohila, A. ; Manca, G. ; Nagy, Z. ; Pilegaard, K. ; Pinter, K. ; Pio, C. ; Raschi, A. ; Rogiers, N. ; Sanz, M.J. ; Stefani, P. ; Sutton, M. ; Tuba, Z. ; Valentini, R. ; Williams, M.L. ; Wohlfahrt, G. - \ 2007
Agriculture, Ecosystems and Environment 121 (2007)1-2. - ISSN 0167-8809 - p. 93 - 120.
graslanden - ecofysiologie - kooldioxide - productiviteit - lichtrelaties - grasslands - ecophysiology - carbon dioxide - productivity - light relations - intercepted solar-radiation - carbon-dioxide exchange - water-vapor exchange - flux measurements - soil respiration - eddy covariance - use efficiency - climate-change - temperate grassland - tallgrass prairie
Tower CO2 flux measurements from 20 European grasslands in the EUROGRASSFLUX data set covering a wide range of environmental and management conditions were analyzed with respect to their ecophysiological characteristics and CO2 exchange (gross primary production, P g, and ecosystem respiration, R e) using light-response function analysis. Photosynthetically active radiation (Q ) and top-soil temperature (T s) were identified as key factors controlling CO2 exchange between grasslands and the atmosphere at the 30-min scale. A nonrectangular hyperbolic light-response model P (Q ) and modified nonrectangular hyperbolic light–temperature-response model P (Q , T s) proved to be flexible tools for modeling CO2 exchange in the light. At night, it was not possible to establish robust instantaneous relationships between CO2 evolution rate r n and environmental drivers, though under certain conditions, a significant relationship rn=r0 ekTTsrn=r0 ekTTs was found using observation windows 7–14 days wide. Principal light-response parameters—apparent quantum yield, saturated gross photosynthesis, daytime ecosystem respiration, and gross ecological light-use efficiency, ɛ = Pg/Q, display patterns of seasonal dynamics which can be formalized and used for modeling. Maximums of these parameters were found in intensively managed grasslands of Atlantic climate. Extensively used semi-natural grasslands of southern and central Europe have much lower production, respiration, and light-use efficiency, while temperate and mountain grasslands of central Europe ranged between these two extremes. Parameters from light–temperature-response analysis of tower data are in agreement with values obtained using closed chambers and free-air CO2 enrichment. Correlations between light-response and productivity parameters provides the possibility to use the easier to measure parameters to estimate the parameters that are more difficult to measure. Gross primary production (Pg) of European grasslands ranges from 1700 g CO2 m−2 year−1 in dry semi-natural pastures to 6900 g CO2 m−2 year−1 in intensively managed Atlantic grasslands. Ecosystem respiration (Re) is in the range 1800 <Re <6000 g CO2 m−2 year−1. Annual net ecosystem CO2 exchange (NEE) varies from significant net uptake (>2400 g CO2 m−2 year−1) to significant release (
Tower CO2 flux measurements from 20 European grasslands in the EUROGRASSFLUX data set covering a wide range of environmental and management conditions were analyzed with respect to their ecophysiological characteristics and CO2 exchange (gross primary production, P-g, and ecosystem respiration, R-e) using light-response function analysis. Photosynthetically active radiation (Q) and top-soil temperature (T-s) were identified as key factors controlling CO2 exchange between grasslands and the atmosphere at the 30-min scale. A nonrectangular hyperbolic light-response model P(Q) and modified nonrectangular hyperbolic light-temperature-response model P(Q, T-s) proved to be flexible tools for modeling CO2 exchange in the light. At night, it was not possible to establish robust instantaneous relationships between CO2 evolution rate r(n) and environmental drivers, though under certain conditions, a significant relationship r(n) = r(0) e(kTTs) was found using observation windows 7-14 days wide. Principal light-response parameters-apparent quantum yield, saturated gross photosynthesis, daytime ecosystem respiration, and gross ecological light-use efficiency, epsilon = P-g/Q, display patterns of seasonal dynamics which can be formalized and used for modeling. Maximums of these parameters were found in intensively managed grasslands of Atlantic climate. Extensively used semi-natural grasslands of southern and central Europe have much lower production, respiration, and light-use efficiency, while temperate and mountain grasslands of central Europe ranged between these two extremes. Parameters from light-temperature-response analysis of tower data are in agreement with values obtained using closed chambers and free-air CO, enrichment. Correlations between light-response and productivity parameters provides the possibility to use the easier to measure parameters to estimate the parameters that are more difficult to measure. Gross primary production (P,) of European grasslands ranges from 1700 g CO2 m(-2) year(-1) in dry semi-natural pastures to 6900 g CO2 m(-2) year(-1) in intensively managed Atlantic grasslands. Ecosystem respiration (R-e) is in the range 1800 <R-e <6000 g CO2 m(-2) year(-1). Annual net ecosystem CO2 exchange (NEE) varies from significant net uptake (> 2400 g CO2 m(-2) year(-1)) to significant release (<-600 g CO2 m(-2) year(-1)), though in 15 out of 19 cases grasslands performed as net CO2 sinks. The carbon source was associated with organic rich soils, grazing, and heat stress. Comparison of P-g, R-e, and NEE for tower sites with the same characteristics from previously published papers obtained with other methods did not reveal significant discrepancies. Preliminary results indicate relationships of grassland P-g and R-e to macroclimatic factors (precipitation and temperature), but these relationships cannot be reduced to simple monofactorial models. (c) 2006 Elsevier B.V. All rights reserved.
Determinants of terrestrial ecosystem carbon balance inferred from European eddy covariance flux sites
Reichstein, M. ; Papale, D. ; Valentini, R. ; Aubinet, M. ; Bernhofer, C. ; Knohl, A. ; Laurila, T. ; Lindroth, A. ; Moors, E.J. ; Pilegaard, K. ; Seufert, G. - \ 2007
Geophysical Research Letters 34 (2007). - ISSN 0094-8276 - 5
netto ecosysteem koolstofbalans - eddy-covariantie - primaire productie - koolstofcyclus - terrestrische ecosystemen - net ecosystem carbon balance - eddy covariance - primary production - carbon cycle - terrestrial ecosystems - spatial variability - water-vapor - respiration - exchange - forests - climate - productivity - temperature - vegetation - dioxide
Pioneering work in the last century has resulted in a widely accepted paradigm that primary production is strongly positively related to temperature and water availability such that the northern hemispheric forest carbon sink may increase under conditions of global warming. However, the terrestrial carbon sink at the ecosystem level (i.e. net ecosystem productivity, NEP) depends on the net balance between gross primary productivity (GPP) and ecosystem respiration (TER). Through an analysis of European eddy covariance flux data sets, we find that the common climate relationships for primary production do not hold for NEP. This is explained by the fact that decreases in GPP are largely compensated by parallel decreases in TER when climatic factors become more limiting. Moreover, we found overall that water availability was a significant modulator of NEP, while the multivariate effect of mean annual temperature is small and not significant. These results indicate that climate- and particularly temperature-based projections of net carbon balance may be misleading. Future research should focus on interactions between the water and carbon cycles and the effects of disturbances on the carbon balance of terrestrial ecosystems.
Fluorescence explorer (FLEX): An optimised payload to map vegetation photosynthesis from space
Moreno, J.F. ; Asner, G.P. ; Bach, H. ; Belenguer, T. ; Bell, A. ; Buschmann, C. ; Calera, A. ; Calpe, J. ; Campbell, P. ; Cecchi, G. ; Colombo, R. ; Corp, L.A. ; Court, A. ; Cutter, M.A. ; Disney, M. ; Dudelzak, A. ; Urso, G. D'; Fernandes, R. ; Flexas, J. ; Gege, P. ; Gielen, B. ; Gitelson, A. ; Gloor, E.U. ; Gower, J. ; Green, R.O. ; Hill, J. ; Jacquemoud, S. ; Jia, L. ; Kneubühler, M. ; Laurila, T. ; Lewis, P. ; Lobb, D. ; Magnani, F. ; Maier, S.W. ; Martinez, A. ; Marek, M.V. ; Martinez Cobo, P. ; Mazzinghi, P. ; Menenti, M. ; Merton, R. ; Middleton, E. ; Miguel, E. De; Miller, J. ; Mohammed, G. ; Milton, E.J. ; Morales, F. ; Moya, I. ; Nedbal, L. ; Knorr, W. ; Ottle, C. ; Olioso, A. ; Pace, S. ; Palucci, A. ; Pedros, R. ; Peltoniemi, J. ; Penuelas, J. ; Plaza, A.J. ; Polcher, J. ; Rascher, U. ; Reuter, R. ; Rosema, A. ; Roujean, J.L. ; Saito, Y. ; Saugier, B. ; Schaepman, M.E. ; Serrano, J.B. ; Settle, J.J. ; Sierra, M. ; Sobrino, J. ; Stoll, M.P. ; Su, Z. ; Tobehn, C. ; Tremblay, N. ; Valcke, R. ; Verhoef, W. ; Veroustraete, F. ; Verstraete, M. ; Zarco Tejada, P. - \ 2006
In: Proceedings AIAA 57th International Astronautical Congress, 2 - 6 October, 2006, Valencia, Spain. - Valencia : AIAA - p. 2065 - 2074.
Pan-European d13C values of air and organic matter from forest ecosystems
Hemming, D. ; Yakir, D. ; Ambus, P. ; Aurela, M. ; Besson, C. ; Black, K. ; Buchmann, N. ; Burlett, R. ; Cescatti, A. ; Clement, R. ; Gross, P. ; Granier, A. ; Grünwald, T. ; Havrankova, K. ; Janous, D. ; Janssens, I.A. ; Knohl, A. ; Köstner, B. ; Kowalski, A. ; Laurila, T. ; Mata, C. ; Marcolla, B. ; Matteucci, G. ; Moncrieff, J. ; Moors, E.J. ; Osborne, B. ; Santos Pereira, J. ; Pihlatie, M. ; Pilegaard, K. ; Ponti, F. ; Rosova, Z. ; Rossi, F. ; Scartazza, A. ; Vesala, T. - \ 2005
Global Change Biology 11 (2005)7. - ISSN 1354-1013 - p. 1065 - 1093.
carbon-isotope discrimination - tree-ring cellulose - below-ground carbon - fossil-fuel co2 - atmospheric co2 - sampling-network - environmental-regulation - dioxide emissions - soil respiration - root respiration
We present carbon stable isotope, delta C-13, results from air and organic matter samples collected during 98 individual field campaigns across a network of Carboeuroflux forest sites in 2001 (14 sites) and 2002 (16 sites). Using these data, we tested the hypothesis that delta C-13 values derived from large-scale atmospheric measurements and models, which are routinely used to partition carbon fluxes between land and ocean, and potentially between respiration and photosynthesis on land, are consistent with directly measured ecosystem-scale delta C-13 values. In this framework, we also tested the potential of delta C-13 in canopy air and plant organic matter to record regional-scale ecophysiological patterns. Our network estimates for the mean delta C-13 of ecosystem respired CO2 and the related 'discrimination' of ecosystem respiration, delta(er) and Delta(er), respectively, were -25.6 +/- 1.9 parts per thousand and 17.8 +/- 2.0 parts per thousand in 2001 and -26.6 +/- 1.5 parts per thousand and 19.0 +/- 1.6 parts per thousand in 2002. The results were in close agreement with delta C-13 values derived from regional-scale atmospheric measurement programs for 2001, but less so in 2002, which had an unusual precipitation pattern. This suggests that regional-scale atmospheric sampling programs generally capture ecosystem delta C-13 signals over Europe, but may be limited in capturing some of the interannual variations. In 2001, but less so in 2002, there were discernable longitudinal and seasonal trends in delta(er). From west to east, across the network, there was a general enrichment in C-13 (similar to 3 parts per thousand and similar to 1 parts per thousand for the 2 years, respectively) consistent with increasing Gorczynski continentality index for warmer and drier conditions. In 2001 only, seasonal C-13 enrichment between July and September, followed by depletion in November (from about -26.0 parts per thousand to -24.5 parts per thousand to -30.0 parts per thousand), was also observed. In 2001, July and August delta(er) values across the network were significantly related to average daytime vapor pressure deficit (VPD), relative humidity (RH), and, to a lesser degree, air temperature (T-a), but not significantly with monthly average precipitation (P-m). In contrast, in 2002 (a much wetter peak season), delta(er) was significantly related with T-a, but not significantly with VPD and RH. The important role of plant physiological processes on delta(er) in 2001 was emphasized by a relatively rapid turnover (between 1 and 6 days) of assimilated carbon inferred from time-lag analyses of delta(er) vs. meteorological parameters. However, this was not evident in 2002. These analyses also noted corresponding diurnal cycles of delta(er) and meteorological parameters in 2001, indicating a rapid transmission of daytime meteorology, via physiological responses, to the delta(er) signal during this season. Organic matter delta C-13 results showed progressive C-13 enrichment from leaves, through stems and roots to soil organic matter, which may be explained by C-13 fractionation during respiration. This enrichment was species dependent and was prominent in angiosperms but not in gymnosperms. delta C-13 values of organic matter of any of the plant components did not well represent short-term delta(er) values during the seasonal cycle, and could not be used to partition ecosystem respiration into autotrophic and heterotrophic components.
Quality analysis applied on eddy covariance measurements at complex forest sites using footprint modelling
Rebmann, C. ; Göckede, M. ; Foken, T. ; Aubinet, M. ; Aurela, M. ; Berbigier, P. ; Bernhofer, C. ; Buchmann, N. ; Carrara, A. ; Cescatti, A. ; Ceulemans, R. ; Clement, R. ; Elbers, J.A. ; Granier, A. ; Grünwald, T. ; Guyon, D. ; Havránková, K. ; Heinesch, B. ; Knohl, A. ; Laurila, T. ; Longdoz, B. ; Marcolla, B. ; Markkanen, T. ; Miglietta, F. ; Moncrieff, J. ; Montagnani, L. ; Moors, E.J. ; Nardino, M. ; Ourcival, J.M. ; Rambal, S. ; Rannik, Ü. ; Rotenberg, E. ; Sedlak, P. ; Unterhuber, G. ; Vesala, T. ; Yakir, D. - \ 2005
Theoretical and Applied Climatology 80 (2005). - ISSN 0177-798X - p. 121 - 141.
carbon sequestration - heterogeneous forest - flux measurements - deciduous forest - beech forest - net carbon - exchange - co2 - atmosphere - balance
Measuring turbulent fluxes with the eddy covariance method has become a widely accepted and powerful tool for the determination of long term data sets for the exchange of momentum, sensible and latent heat, and trace gases such as CO2 between the atmosphere and the underlying surface. Several flux networks developed continuous measurements above complex terrain, e.g. AmeriFlux and EUROFLUX, with a strong focus on the net exchange of CO2 between the atmosphere and the underlying surface. Under many conditions basic assumptions for the eddy covariance method in its simplified form, such as stationarity of the flow, homogeneity of the surface and fully developed turbulence of the flow field, are not fulfilled. To deal with non-ideal conditions which are common at many FLUXNET sites, quality tests have been developed to check if these basic theoretical assumptions are valid. In the framework of the CARBOEUROFLUX project, we combined quality tests described by Foken and Wichura (1996) with the analytical footprint model of Schmid (1997). The aim was to identify suitable wind sectors and meteorological conditions for flux measurements. These tools were used on data of 18 participating sites. Quality tests were applied on the fluxes of momentum, sensible and latent heat, and on the CO2-flux, respectively. The influence of the topography on the vertical wind component was also checked. At many sites the land use around the flux towers is not homogeneous or the fetch may not be large enough. So the relative contribution of the land use type intended to be measured was also investigated. Thus the developed tool allows comparative investigations of the measured turbulent fluxes at different sites if using the same technique and algorithms for the determination of the fluxes as well as analyses of potential problems caused by influences of the surrounding land use patterns
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