Browsing by Subject "NET ECOSYSTEM EXCHANGE"

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  • Peltoniemi, Mikko; Pulkkinen, Minna; Aurela, Mika; Pumpanen, Jukka; Kolari, Pasi; Makela, Annikki (2015)
    Simple approaches to predicting ecosystem fluxes are useful in large-scale applications because existing data rarely support justified use of complex models. We developed a model of daily ecosystem gross primary production (P), evapotranspiration (E), and soil water content (theta), which only requires standard weather data and information about the fraction of absorbed radiation. We estimated the parameters of the model for two boreal Scots pine eddy-covariance sites (Hyytiala and Sodankyla). The model predicted P and E adequately for Hyytiala for both calibration and additional test years. The model calibrated for Hyytiala slightly overestimated P and E in Sodankyla, but its performance levelled with the model calibrated for Sodankyla in a dry year. Sensitivity analysis of the model implied that drought prediction is sensitive, not only to key E submodel parameters, but also to P submodel parameters. Further improvement and calibrations of the model could benefit from forest sites with varying canopy and different species structures.
  • Stoy, P. C.; Richardson, A. D.; Baldocchi, D. D.; Katul, G. G.; Stanovick, J.; Mahecha, M. D.; Reichstein, M.; Detto, M.; Law, B. E.; Wohlfahrt, G.; Arriga, N.; Campos, J.; McCaughey, J. H.; Montagnani, L.; U, K. T. Paw; Sevanto, S.; Williams, M. (2009)
  • Kooijmans, Linda M. J.; Maseyk, Kadmiel; Seibt, Ulli; Sun, Wu; Vesala, Timo; Mammarella, Ivan; Kolari, Pasi; Aalto, Juho; Franchin, Alessandro; Vecchi, Roberta; Valli, Gianluigi; Chen, Huilin (2017)
    Nighttime vegetative uptake of carbonyl sulfide (COS) can exist due to the incomplete closure of stomata and the light independence of the enzyme carbonic anhydrase, which complicates the use of COS as a tracer for gross primary productivity (GPP). In this study we derived night-time COS fluxes in a boreal forest (the SMEAR II station in Hyytiala, Finland; 61 degrees 51 ' N, 24 degrees 17 ' E; 181ma.s.l.) from June to November 2015 using two different methods: eddy-covariance (EC) measurements (FCOS-EC) and the radon-tracer method (FCOS-Rn). The total night-time COS fluxes averaged over the whole measurement period were -6.8 +/- 2.2 and -7.9 +/- 3.8 pmolm (-2) s (-1) for FCOS-Rn and FCOS-EC, respectively, which is 33-38% of the average daytime fluxes and 21% of the total daily COS uptake. The correlation of Rn-222 (of which the source is the soil) with COS (average R-2 = 0.58) was lower than with CO2 (0.70), suggesting that the main sink of COS is not located at the ground. These observations are supported by soil chamber measurements that show that soil contributes to only 34-40% of the total night-time COS uptake. We found a decrease in COS uptake with decreasing nighttime stomatal conductance and increasing vapor-pressure deficit and air temperature, driven by stomatal closure in response to a warm and dry period in August. We also discuss the effect that canopy layer mixing can have on the radon-tracer method and the sensitivity of (FCOS-EC) to atmospheric turbulence. Our results suggest that the nighttime uptake of COS is mainly driven by the tree foliage and is significant in a boreal forest, such that it needs to be taken into account when using COS as a tracer for GPP.
  • Alekseychik, Pavel; Korrensalo, Aino; Mammarella, Ivan; Launiainen, Samuli; Tuittila, Eeva-Stiina; Korpela, Ilkka; Vesala, Timo (2021)
    Pristine boreal mires are known as substantial sinks of carbon dioxide (CO2) and net emitters of methane (CH4). Bogs constitute a major fraction of pristine boreal mires. However, the bog CO2 and CH4 balances are poorly known, having been largely estimated based on discrete and short-term measurements by manual chambers and seldom using the eddy-covariance (EC) technique. Eddy-covariance (EC) measurements of CO2 and CH4 exchange were conducted in the Siikaneva mire complex in southern Finland in 2011-2016. The site is a patterned bog having a moss-sedge-shrub vegetation typical of southern Eurasian taiga, with several ponds near the EC tower. The study presents a complete series of CO2 and CH4 EC flux (F-CH4) measurements and identifies the environmental factors controlling the ecosystem-atmosphere CO2 and CH4 exchange. A 6-year average growing season (May-September) cumulative CO2 exchange of -61 +/- 24 g Cm-2 was observed, which partitions into mean total respiration (Re) of 167 +/- 33 (interannual range 146-197) g Cm-2 and mean gross primary production (GPP) of 228 +/- 46 (interannual range 193-257) g Cm-2, while the corresponding F-CH4 amounts to 7.1 +/- 0.7 (interannual range 6.4-8.4) g Cm-2. The contribution of October-December CO2 and CH4 fluxes to the cumulative sums was not negligible based on the measurements during one winter. GPP, Re and F-CH4 increased with temperature. GPP and F-CH4 did not show any significant decline even after a substantial water table drawdown in 2011. Instead, GPP, Re and F-CH4 were limited in the cool, cloudy and wet growing season of 2012. May-September cumulative net ecosystem exchange (NEE) of 2013-2016 averaged at about 73 g Cm-2, in contrast with the hot and dry year 2011 and the wet and cool year 2012. Suboptimal weather likely reduced the net sink by about 25 g Cm-2 in 2011 due to elevated Re, and by about 40 g Cm-2 in 2012 due to limited GPP. The cumulative growing season sums of GPP and CH4 emission showed a strong positive relationship. The EC source area was found to be comprised of eight distinct surface types. However, footprint analyses revealed that contributions of different surface types varied only within 10 %-20% with respect to wind direction and stability conditions. Consequently, no clear link between CO2 and CH4 fluxes and the EC footprint composition was found despite the apparent variation in fluxes with wind direction.
  • Flechard, Chris R.; van Oijen, Marcel; Cameron, David R.; de Vries, Wim; Ibrom, Andreas; Buchmann, Nina; Dise, Nancy B.; Janssens, Ivan A.; Neirynck, Johan; Montagnani, Leonardo; Varlagin, Andrej; Loustau, Denis; Legout, Arnaud; Ziemblinska, Klaudia; Aubinet, Marc; Aurela, Mika; Chojnicki, Bogdan H.; Drewer, Julia; Eugster, Werner; Francez, Andre-Jean; Juszczak, Radoslaw; Kitzler, Barbara; Kutsch, Werner L.; Lohila, Annalea; Longdoz, Bernard; Matteucci, Giorgio; Moreaux, Virginie; Nefte, Albrecht; Olejnik, Janusz; Sanz, Maria J.; Siemens, Jan; Vesala, Timo; Vincke, Caroline; Nemitz, Eiko; Zechmeister-Boltenstern, Sophie; Butterbach-Bahl, Klaus; Skiba, Ute M.; Sutton, Mark A. (2020)
    The effects of atmospheric nitrogen deposition (N-dep) on carbon (C) sequestration in forests have often been assessed by relating differences in productivity to spatial variations of N-dep across a large geographic domain. These correlations generally suffer from covariation of other confounding variables related to climate and other growth-limiting factors, as well as large uncertainties in total (dry + wet) reactive nitrogen (N-r) deposition. We propose a methodology for untangling the effects of N-dep from those of meteorological variables, soil water retention capacity and stand age, using a mechanistic forest growth model in combination with eddy covariance CO2 exchange fluxes from a Europe-wide network of 22 forest flux towers. Total N-r deposition rates were estimated from local measurements as far as possible. The forest data were compared with data from natural or semi-natural, non-woody vegetation sites. The response of forest net ecosystem productivity to nitrogen deposition (dNEP/dN(dep)) was estimated after accounting for the effects on gross primary productivity (GPP) of the co-correlates by means of a meta-modelling standardization procedure, which resulted in a reduction by a factor of about 2 of the uncorrected, apparent dGPP/dN(dep) value. This model-enhanced analysis of the C and N-dep flux observations at the scale of the European network suggests a mean overall dNEP/dN(dep) response of forest lifetime C sequestration to N-dep of the order of 40-50 g C per g N, which is slightly larger but not significantly different from the range of estimates published in the most recent reviews. Importantly, patterns of gross primary and net ecosystem productivity versus N-dep were non-linear, with no further growth responses at high N-dep levels (N-dep > 2.5-3 gNm(-2) yr(-1)) but accompanied by increasingly large ecosystem N losses by leaching and gaseous emissions. The reduced increase in productivity per unit N deposited at high N-dep levels implies that the forecast increased N-r emissions and increased N-dep levels in large areas of Asia may not positively impact the continent's forest CO2 sink. The large level of unexplained variability in observed carbon sequestration efficiency (CSE) across sites further adds to the uncertainty in the dC/dN response.
  • Zona, Donatella; Gioli, Beniamino; Commane, Roisin; Lindaas, Jakob; Wofsy, Steven C.; Miller, Charles E.; Dinardo, Steven J.; Dengel, Sigrid; Sweeney, Colm; Karion, Anna; Chang, Rachel Y. -W.; Henderson, John M.; Murphy, Patrick C.; Goodrich, Jordan P.; Moreaux, Virginie; Liljedahl, Anna; Watts, Jennifer D.; Kimball, John S.; Lipson, David A.; Oechel, Walter C. (2016)
    Arctic terrestrial ecosystems are major global sources of methane (CH4); hence, it is important to understand the seasonal and climatic controls on CH4 emissions from these systems. Here, we report year-round CH4 emissions from Alaskan Arctic tundra eddy flux sites and regional fluxes derived from aircraft data. We find that emissions during the cold season (September to May) account for >= 50% of the annual CH4 flux, with the highest emissions from noninundated upland tundra. A major fraction of cold season emissions occur during the "zero curtain" period, when subsurface soil temperatures are poised near 0 degrees C. The zero curtain may persist longer than the growing season, and CH4 emissions are enhanced when the duration is extended by a deep thawed layer as can occur with thick snow cover. Regional scale fluxes of CH4 derived from aircraft data demonstrate the large spatial extent of late season CH4 emissions. Scaled to the circumpolar Arctic, cold season fluxes from tundra total 12 +/- 5 (95% confidence interval) Tg CH4 y(-1), similar to 25% of global emissions from extratropical wetlands, or similar to 6% of total global wetland methane emissions. The dominance of late-season emissions, sensitivity to soil environmental conditions, and importance of dry tundra are not currently simulated in most global climate models. Because Arctic warming disproportionally impacts the cold season, our results suggest that higher cold-season CH4 emissions will result from observed and predicted increases in snow thickness, active layer depth, and soil temperature, representing important positive feedbacks on climate warming.
  • Durand, Maxime; Murchie, Erik H.; Lindfors, Anders; Urban, Otmar; Aphalo, Pedro J.; Robson, T. Matthew (2021)
    The sunlight received by plants is affected by cloudiness and pollution. Future changes in cloud cover will differ among regions, while aerosol concentrations are expected to continue increasing globally as a result of wildfires, fossil fuel combustion, and industrial pollution. Clouds and aerosols increase the diffuse fraction and modify the spectral composition of incident solar radiation, and both will affect photosynthesis and terrestrial ecosystem productivity. Thus, an assessment of how canopy and leaf-level processes respond to these changes is needed as part of accurately forecasting future global carbon assimilation. To review these processes and their implications: first, we discuss the physical basis of the effect of clouds and aerosols on solar radiation as it penetrates the atmosphere; second, we consider how direct and diffuse radiation are absorbed and transmitted by plant canopies and their leaves; and finally, we assess the consequences for photosynthesis at the canopy and ecosystem levels. Photobiology will be affected at the atmospheric level by a shift in spectral composition toward shorter or longer wavelengths under clouds or aerosols, respectively, due to different scattering. Changes in the microclimate and spectral composition of radiation due to an enhanced diffuse fraction also depend on the acclimation of canopy architectural and physiological traits, such as leaf area index, orientation, and clumping. Together with an enhancement of light-use efficiency, this makes the effect of diffuse solar radiation on canopy photosynthesis a multilayered phenomenon, requiring experimental testing to capture those complex interactions that will determine whether it produces the persistent enhancement in carbon assimilation that land-surface models currently predict.
  • Launiainen, Samuli; Katul, Gabriel G.; Leppä, Kersti; Kolari, Pasi; Aslan, Toprak; Grönholm, Tiia; Korhonen, Lauri; Mammarella, Ivan; Vesala, Timo (2022)
    The terrestrial net ecosystem productivity (NEP) has increased during the past three decades, but the mechanisms responsible are still unclear. We analyzed 17 years (2001-2017) of eddy-covariance measurements of NEP, evapotranspiration (ET) and light and water use efficiency from a boreal coniferous forest in Southern Finland for trends and inter-annual variability (IAV). The forest was a mean annual carbon sink (252 [+/- 42] gC m-2a-1), and NEP increased at rate +6.4-7.0 gC m-2a-1 (or ca. +2.5% a-1) during the period. This was attributed to the increasing gross-primary productivity GPP and occurred without detectable change in ET. The start of annual carbon uptake period was advanced by 0.7 d a-1, and increase in GPP and NEP outside the main growing season contributed ca. one-third and one-fourth of the annual trend, respectively. Meteorological factors were responsible for the IAV of fluxes but did not explain the long-term trends. The growing season GPP trend was strongest in ample light during the peak growing season. Using a multi-layer ecosystem model, we showed that direct CO2 fertilization effect diminishes when moving from leaf to ecosystem, and only 30-40% of the observed ecosystem GPP increase could be attributed to CO2. The increasing trend in leaf-area index (LAI), stimulated by forest thinning in 2002, was the main driver of the enhanced GPP and NEP of the mid-rotation managed forest. It also compensated for the decrease of mean leaf stomatal conductance with increasing CO2 and LAI, explaining the apparent proportionality between observed GPP and CO2 trends. The results emphasize that attributing trends to their physical and physiological drivers is challenged by strong IAV, and uncertainty of LAI and species composition changes due to the dynamic flux footprint. The results enlighten the underlying mechanisms responsible for the increasing terrestrial carbon uptake in the boreal zone.
  • Montagnani, Leonardo; Gruenwald, Thomas; Kowalski, Andrew; Mammarella, Ivan; Merbold, Lutz; Metzger, Stefan; Sedlak, Pavel; Siebicke, Lukas (2018)
    In eddy covariance measureinents, the storage flux represents the variation in time of the dry molar fraction of a given gas in the control volume representative of turbulent flux. Depending on the time scale considered, and on the height above ground of the measurements, it can either be a major component of the overall net ecosystem exchange or nearly negligible. Instrumental configuration and computational procedures must be optimized to measure this change at the time step used for the turbulent flux measurement Three different configurations are suitable within the Integrated Carbon Observation System infrastructure for the storage flux determination: separate sampling, subsequent sampling and mixed sampling. These configurations have their own advantages and disadvantages, and must be carefully selected based on the specific features of the considered station. In this paper, guidelines about number and distribution of vertical and horizontal sampling points are given. Details about suitable instruments, sampling devices, and computational procedures for the quantification of the storage flux of different GHG gases are also provided.
  • Rebmann, Corinna; Aubinet, Marc; Schmid, Hape; Arriga, Nicola; Aurela, Mika; Burba, George; Clement, Robert; De Ligne, Anne; Fratini, Gerardo; Gielen, Bert; Grace, John; Graf, Alexander; Gross, Patrick; Haapanala, Sami; Herbst, Mathias; Hortnagl, Lukas; Ibrom, Andreas; Joly, Lilian; Kljun, Natascha; Kolle, Olaf; Kowalski, Andrew; Lindroth, Anders; Loustau, Denis; Mammarella, Ivan; Mauder, Matthias; Merbold, Lutz; Metzger, Stefan; Molder, Meelis; Montagnani, Leonardo; Papale, Dario; Pavelka, Marian; Peichl, Matthias; Roland, Marilyn; Serrano-Ortiz, Penelope; Siebicke, Lukas; Steinbrecher, Rainer; Tuovinen, Juha-Pekka; Vesala, Timo; Wohlfahrt, Georg; Franz, Daniela (2018)
    The Integrated Carbon Observation System Re-search Infrastructure aims to provide long-term, continuous observations of sources and sinks of greenhouse gases such as carbon dioxide, methane, nitrous oxide, and water vapour. At ICOS ecosystem stations, the principal technique for measurements of ecosystem-atmosphere exchange of GHGs is the eddy-covariance technique. The establishment and setup of an eddy-covariance tower have to be carefully reasoned to ensure high quality flux measurements being representative of the investigated ecosystem and comparable to measurements at other stations. To fulfill the requirements needed for flux determination with the eddy-covariance technique, variations in GHG concentrations have to be measured at high frequency, simultaneously with the wind velocity, in order to fully capture turbulent fluctuations. This requires the use of high-frequency gas analysers and ultrasonic anemometers. In addition, to analyse flux data with respect to environmental conditions but also to enable corrections in the post-processing procedures, it is necessary to measure additional abiotic variables in close vicinity to the flux measurements. Here we describe the standards the ICOS ecosystem station network has adopted for GHG flux measurements with respect to the setup of instrumentation on towers to maximize measurement precision and accuracy while allowing for flexibility in order to observe specific ecosystem features.
  • Bacour, C.; Maignan, F.; MacBean, N.; Porcar-Castell, A.; Flexas, J.; Frankenberg, C.; Peylin, P.; Chevallier, F.; Vuichard, N.; Bastrikov, V. (2019)
    Abstract Over the last few years, solar-induced chlorophyll fluorescence (SIF) observations from space have emerged as a promising resource for evaluating the spatio-temporal distribution of gross primary productivity (GPP) simulated by global terrestrial biosphere models. SIF can be used to improve GPP simulations by optimizing critical model parameters through statistical Bayesian data assimilation techniques. A prerequisite is the availability of a functional link between GPP and SIF in terrestrial biosphere models. Here we present the development of a mechanistic SIF observation operator in the ORCHIDEE (Organizing Carbon and Hydrology In Dynamic Ecosystems) terrestrial biosphere model. It simulates the regulation of photosystem II fluorescence quantum yield at the leaf level thanks to a novel parameterization of non-photochemical quenching as a function of temperature, photosynthetically active radiation, and normalized quantum yield of photochemistry. It emulates the radiative transfer of chlorophyll fluorescence to the top of the canopy using a parametric simplification of the SCOPE (Soil Canopy Observation Photosynthesis Energy) model. We assimilate two years of monthly OCO-2 (Orbiting Carbon Observatory-2) SIF product at 0.5° (2015?2016) to optimize ORCHIDEE photosynthesis and phenological parameters over an ensemble of grid points for all plant functional types. The impact on the simulated GPP is considerable with a large decrease of the global scale budget by 28 GtC/year over the period 1990?2009. The optimized GPP budget (134/136 GtC/year over 1990?2009/2001?2009) remarkably agrees with independent GPP estimates, FLUXSAT (137 GtC/year over 2001?2009) in particular and FLUXCOM (121 GtC/year over 1990?2009). Our results also suggest a biome dependency of the SIF-GPP relationship that needs to be improved for some plant functional types.
  • Peltola, Olli; Vesala, Timo; Gao, Yao; Raty, Olle; Alekseychik, Pavel; Aurela, Mika; Chojnicki, Bogdan; Desai, Ankur R.; Dolman, Albertus J.; Euskirchen, Eugenie S.; Friborg, Thomas; Goeckede, Mathias; Helbig, Manuel; Humphreys, Elyn; Jackson, Robert B.; Jocher, Georg; Joos, Fortunat; Klatt, Janina; Knox, Sara H.; Kowalska, Natalia; Kutzbach, Lars; Lienert, Sebastian; Lohila, Annalea; Mammarella, Ivan; Nadeau, Daniel F.; Nilsson, Mats B.; Oechel, Walter C.; Peichl, Matthias; Pypker, Thomas; Quinton, William; Rinne, Janne; Sachs, Torsten; Samson, Mateusz; Schmid, Hans Peter; Sonnentag, Oliver; Wille, Christian; Zona, Donatella; Aalto, Tuula (2019)
    Natural wetlands constitute the largest and most uncertain source of methane (CH4) to the atmosphere and a large fraction of them are found in the northern latitudes. These emissions are typically estimated using process ("bottom-up") or inversion ("top-down") models. However, estimates from these two types of models are not independent of each other since the top-down estimates usually rely on the a priori estimation of these emissions obtained with process models. Hence, independent spatially explicit validation data are needed. Here we utilize a random forest (RF) machine-learning technique to upscale CH4 eddy covariance flux measurements from 25 sites to estimate CH4 wetland emissions from the northern latitudes (north of 45 degrees N). Eddy covariance data from 2005 to 2016 are used for model development. The model is then used to predict emissions during 2013 and 2014. The predictive performance of the RF model is evaluated using a leave-one-site-out cross-validation scheme. The performance (Nash-Sutcliffe model efficiency = 0.47) is comparable to previous studies upscaling net ecosystem exchange of carbon dioxide and studies comparing process model output against site-level CH4 emission data. The global distribution of wetlands is one major source of uncertainty for upscaling CH4. Thus, three wetland distribution maps are utilized in the upscaling. Depending on the wetland distribution map, the annual emissions for the northern wetlands yield 32 (22.3-41.2, 95% confidence interval calculated from a RF model ensemble), 31 (21.4-39.9) or 38 (25.9-49.5) Tg(CH4) yr(-1). To further evaluate the uncertainties of the upscaled CH4 flux data products we also compared them against output from two process models (LPX-Bern and WetCHARTs), and methodological issues related to CH4 flux upscaling are discussed. The monthly upscaled CH4 flux data products are available at https://doi.org/10.5281/zenodo.2560163.
  • Lasslop, G.; Migliavacca, M.; Bohrer, G.; Reichstein, M.; Bahn, M.; Ibrom, A.; Jacobs, C.; Kolari, P.; Papale, D.; Vesala, T.; Wohlfahrt, G.; Cescatti, A. (2012)
  • Zhang, Zhaoying; Zhang, Yongguang; Porcar-Castell, Albert; Joiner, Joanna; Guanter, Luis; Yang, Xi; Migliavacca, Mirco; Ju, Weimin; Sun, Zhigang; Chen, Shiping; Martini, David; Zhang, Qian; Li, Zhaohui; Cleverly, James; Wang, Hezhou; Goulas, Yves (2020)
    Quantifying global photosynthesis remains a challenge due to a lack of accurate remote sensing proxies. Solar-induced chlorophyll fluorescence (SIF) has been shown to be a good indicator of photosynthetic activity across various spatial scales. However, a global and spatially challenging estimate of terrestrial gross primary production (GPP) based on satellite SIF remains unresolved due to the confounding effects of species-specific physical and physiological traits and external factors, such as canopy structure or photosynthetic pathway (C-3 or C-4). Here we analyze an ensemble of far-red SIF data from OCO-2 satellite and ground observations at multiple sites, using the spectral invariant theory to reduce the effects of canopy structure and to retrieve a structure-corrected total canopy SIF emission (SIFtotal). We find that the relationships between observed canopy-leaving SIF and ecosystem GPP vary significantly among biomes. In contrast, the relationships between SIFtotal and GPP converge around two unique models, one for C-3 and one for C-4 plants. We show that the two single empirical models can be used to globally scale satellite SIF observations to terrestrial GPP. We obtain an independent estimate of global terrestrial GPP of 129.56 +/- 6.54 PgC/year for the 2015-2017 period, which is consistent with the state-of-the-art data- and process-oriented models. The new GPP product shows improved sensitivity to previously undetected 'hotspots' of productivity, being able to resolve the double-peak in GPP due to rotational cropping systems. We suggest that the direct scheme to estimate GPP presented here, which is based on satellite SIF, may open up new possibilities to resolve the dynamics of global terrestrial GPP across space and time.
  • Korrensalo, Aino; Alekseychik, Pavel; Hajek, Tomas; Rinne, Janne; Vesala, Timo; Mehtätalo, Lauri; Mammarella, Ivan; Tuittila, Eeva-Stiina (2017)
    In boreal bogs plant species are low in number, but they differ greatly in their growth forms and photosynthetic properties. We assessed how ecosystem carbon (C) sink dynamics were affected by seasonal variations in the photosynthetic rate and leaf area of different species. Photosynthetic properties (light response parameters), leaf area development and areal cover (abundance) of the species were used to quantify species-specific net and gross photosynthesis rates (P-N and P-G, respectively), which were summed to express ecosystem-level P-N and P-G. The ecosystem-level P-G was compared with a gross primary production (GPP) estimate derived from eddy covariance (EC) measurements. Species areal cover, rather than differences in photosynthetic properties, determined the species with the highest P-G of both vascular plants and Sphagna. Species-specific contributions to the ecosystem P-G varied over the growing season, which, in turn, determined the seasonal variation in ecosystem P-G. The upscaled growing season P-G estimate, 230 gCm (-2), agreed well with the GPP estimated by the EC (243 gCm (-2)). Sphagna were superior to vascular plants in ecosystemlevel P-G throughout the growing season but had a lower P-N. P-N results indicated that areal cover of the species, together with their differences in photosynthetic parameters, shape the ecosystem-level C balance. Species with low areal cover but high photosynthetic efficiency appear to be potentially important for the ecosystem C sink. Results imply that func-tional diversity, i. e., the presence of plant groups with different seasonal timing and efficiency of photosynthesis, may increase the stability of C sinks of boreal bogs.
  • Ducker, Jason A.; Holmes, Christopher D.; Keenan, Trevor F.; Fares, Silvano; Goldstein, Allen H.; Mammarella, Ivan; Munger, J. William; Schnell, Jordan (2018)
    We develop and evaluate a method to estimate O-3 deposition and stomatal O-3 uptake across networks of eddy covariance flux tower sites where O-3 concentrations and O-3 fluxes have not been measured. The method combines standard micrometeorological flux measurements, which constrain O-3 deposition velocity and stomatal conductance, with a gridded dataset of observed surface O-3 concentrations. Measurement errors are propagated through all calculations to quantify O-3 flux uncertainties. We evaluate the method at three sites with O(3 )flux measurements: Harvard Forest, Blodgett Forest, and Hyytiala Forest. The method reproduces 83 % or more of the variability in daily stomatal uptake at these sites with modest mean bias (21 % or less). At least 95 % of daily average values agree with measurements within a factor of 2 and, according to the error analysis, the residual differences from measured O-3 fluxes are consistent with the uncertainty in the underlying measurements. The product, called synthetic O-3 flux or SynFlux, includes 43 FLUXNET sites in the United States and 60 sites in Europe, totaling 926 site years of data. This dataset, which is now public, dramatically expands the number and types of sites where O-3 fluxes can be used for ecosystem impact studies and evaluation of air quality and climate models. Across these sites, the mean stomatal conductance and O-3 deposition velocity is 0.03-1.0 cm s(-1). The stomatal O-3 flux during the growing season (typically April-September) is 0.5-11.0 nmol O-3 m(-2) s(-1) with a mean of 4.5 nmol O(3 )m(-2) s(-1) and the largest fluxes generally occur where stomatal conductance is high, rather than where O-3 concentrations are high. The conductance differences across sites can be explained by atmospheric humidity, soil moisture, vegetation type, irrigation, and land management. These stomatal fluxes suggest that ambient O-3 degrades biomass production and CO2 sequestration by 20 %-24 % at crop sites, 6 %-29 % at deciduous broadleaf forests, and 4 %-20 % at evergreen needleleaf forests in the United States and Europe.
  • van der Molen, M. K.; de Jeu, R. A. M.; Wagner, W.; van der Velde, I. R.; Kolari, P.; Kurbatova, J.; Varlagin, A.; Maximov, T. C.; Kononov, A. V.; Ohta, T.; Kotani, A.; Krol, M. C.; Peters, W. (2016)
    Boreal Eurasia is a region where the interaction between droughts and the carbon cycle may have significant impacts on the global carbon cycle. Yet the region is extremely data sparse with respect to meteorology, soil moisture, and carbon fluxes as compared to e.g. Europe. To better constrain our vegetation model SiBCASA, we increase data usage by assimilating two streams of satellite-derived soil moisture. We study whether the assimilation improved SiBCASA's soil moisture and its effect on the simulated carbon fluxes. By comparing to unique in situ soil moisture observations, we show that the passive microwave soil moisture product did not improve the soil moisture simulated by SiBCASA, but the active data seem promising in some aspects. The match between SiBCASA and ASCAT soil moisture is best in the summer months over low vegetation. Nevertheless, ASCAT failed to detect the major droughts occurring between 2007 and 2013. The performance of ASCAT soil moisture seems to be particularly sensitive to ponding, rather than to biomass. The effect on the simulated carbon fluxes is large, 5-10% on annual GPP and TER, tens of percent on local NEE, and 2% on area-integrated NEE, which is the same order of magnitude as the inter-annual variations. Consequently, this study shows that assimilation of satellite-derived soil moisture has potentially large impacts, while at the same time further research is needed to understand under which conditions the satellite-derived soil moisture improves the simulated soil moisture.
  • Pastorello, Gilberto; Trotta, Carlo; Canfora, Eleonora; Chu, Housen; Christianson, Danielle; Cheah, You-Wei; Poindexter, Cristina; Chen, Jiquan; Elbashandy, Abdelrahman; Humphrey, Marty; Isaac, Peter; Polidori, Diego; Ribeca, Alessio; van Ingen, Catharine; Zhang, Leiming; Amiro, Brian; Ammann, Christof; Arain, M. Altaf; Ardo, Jonas; Arkebauer, Timothy; Arndt, Stefan K.; Arriga, Nicola; Aubinet, Marc; Aurela, Mika; Baldocchi, Dennis; Barr, Alan; Beamesderfer, Eric; Marchesini, Luca Belelli; Bergeron, Onil; Beringer, Jason; Bernhofer, Christian; Berveiller, Daniel; Billesbach, Dave; Black, Thomas Andrew; Blanken, Peter D.; Bohrer, Gil; Boike, Julia; Bolstad, Paul V.; Bonal, Damien; Bonnefond, Jean-Marc; Bowling, David R.; Bracho, Rosvel; Brodeur, Jason; Bruemmer, Christian; Buchmann, Nina; Burban, Benoit; Burns, Sean P.; Buysse, Pauline; Cale, Peter; Cavagna, Mauro; Cellier, Pierre; Chen, Shiping; Chini, Isaac; Christensen, Torben R.; Cleverly, James; Collalti, Alessio; Consalvo, Claudia; Cook, Bruce D.; Cook, David; Coursolle, Carole; Cremonese, Edoardo; Curtis, Peter S.; D'Andrea, Ettore; da Rocha, Humberto; Dai, Xiaoqin; Davis, Kenneth J.; De Cinti, Bruno; de Grandcourt, Agnes; De Ligne, Anne; De Oliveira, Raimundo C.; Delpierre, Nicolas; Desai, Ankur R.; Di Bella, Carlos Marcelo; di Tommasi, Paul; Dolman, Han; Domingo, Francisco; Dong, Gang; Dore, Sabina; Duce, Pierpaolo; Dufrene, Eric; Dunn, Allison; Dusek, Jiri; Eamus, Derek; Eichelmann, Uwe; ElKhidir, Hatim Abdalla M.; Eugster, Werner; Ewenz, Cacilia M.; Ewers, Brent; Famulari, Daniela; Fares, Silvano; Feigenwinter, Iris; Feitz, Andrew; Fensholt, Rasmus; Filippa, Gianluca; Fischer, Marc; Frank, John; Galvagno, Marta; Gharun, Mana; Gianelle, Damiano; Gielen, Bert; Gioli, Beniamino; Gitelson, Anatoly; Goded, Ignacio; Goeckede, Mathias; Goldstein, Allen H.; Gough, Christopher M.; Goulden, Michael L.; Graf, Alexander; Griebel, Anne; Gruening, Carsten; Gruenwald, Thomas; Hammerle, Albin; Han, Shijie; Han, Xingguo; Hansen, Birger Ulf; Hanson, Chad; Hatakka, Juha; He, Yongtao; Hehn, Markus; Heinesch, Bernard; Hinko-Najera, Nina; Hoertnagl, Lukas; Hutley, Lindsay; Ibrom, Andreas; Ikawa, Hiroki; Jackowicz-Korczynski, Marcin; Janous, Dalibor; Jans, Wilma; Jassal, Rachhpal; Jiang, Shicheng; Kato, Tomomichi; Khomik, Myroslava; Klatt, Janina; Knohl, Alexander; Knox, Sara; Kobayashi, Hideki; Koerber, Georgia; Kolle, Olaf; Kosugi, Yoshiko; Kotani, Ayumi; Kowalski, Andrew; Kruijt, Bart; Kurbatova, Julia; Kutsch, Werner L.; Kwon, Hyojung; Launiainen, Samuli; Laurila, Tuomas; Law, Bev; Leuning, Ray; Li, Yingnian; Liddell, Michael; Limousin, Jean-Marc; Lion, Marryanna; Liska, Adam J.; Lohila, Annalea; Lopez-Ballesteros, Ana; Lopez-Blanco, Efren; Loubet, Benjamin; Loustau, Denis; Lucas-Moffat, Antje; Lueers, Johannes; Ma, Siyan; Macfarlane, Craig; Magliulo, Vincenzo; Maier, Regine; Mammarella, Ivan; Manca, Giovanni; Marcolla, Barbara; Margolis, Hank A.; Marras, Serena; Massman, William; Mastepanov, Mikhail; Matamala, Roser; Matthes, Jaclyn Hatala; Mazzenga, Francesco; McCaughey, Harry; McHugh, Ian; McMillan, Andrew M. S.; Merbold, Lutz; Meyer, Wayne; Meyers, Tilden; Miller, Scott D.; Minerbi, Stefano; Moderow, Uta; Monson, Russell K.; Montagnani, Leonardo; Moore, Caitlin E.; Moors, Eddy; Moreaux, Virginie; Moureaux, Christine; Munger, J. William; Nakai, Taro; Neirynck, Johan; Nesic, Zoran; Nicolini, Giacomo; Noormets, Asko; Northwood, Matthew; Nosetto, Marcelo; Nouvellon, Yann; Novick, Kimberly; Oechel, Walter; Olesen, Jorgen Eivind; Ourcival, Jean-Marc; Papuga, Shirley A.; Parmentier, Frans-Jan; Paul-Limoges, Eugenie; Pavelka, Marian; Peichl, Matthias; Pendall, Elise; Phillips, Richard P.; Pilegaard, Kim; Pirk, Norbert; Posse, Gabriela; Powell, Thomas; Prasse, Heiko; Prober, Suzanne M.; Rambal, Serge; Rannik, Ullar; Raz-Yaseef, Naama; Reed, David; de Dios, Victor Resco; Restrepo-Coupe, Natalia; Reverter, Borja R.; Roland, Marilyn; Sabbatini, Simone; Sachs, Torsten; Saleska, Scott R.; Sanchez-Canete, Enrique P.; Sanchez-Mejia, Zulia M.; Schmid, Hans Peter; Schmidt, Marius; Schneider, Karl; Schrader, Frederik; Schroder, Ivan; Scott, Russell L.; Sedlak, Pavel; Serrano-Ortiz, Penelope; Shao, Changliang; Shi, Peili; Shironya, Ivan; Siebicke, Lukas; Sigut, Ladislav; Silberstein, Richard; Sirca, Costantino; Spano, Donatella; Steinbrecher, Rainer; Stevens, Robert M.; Sturtevant, Cove; Suyker, Andy; Tagesson, Torbern; Takanashi, Satoru; Tang, Yanhong; Tapper, Nigel; Thom, Jonathan; Tiedemann, Frank; Tomassucci, Michele; Tuovinen, Juha-Pekka; Urbanski, Shawn; Valentini, Riccardo; van der Molen, Michiel; van Gorsel, Eva; van Huissteden, Ko; Varlagin, Andrej; Verfaillie, Joseph; Vesala, Timo; Vincke, Caroline; Vitale, Domenico; Vygodskaya, Natalia; Walker, Jeffrey P.; Walter-Shea, Elizabeth; Wang, Huimin; Weber, Robin; Westermann, Sebastian; Wille, Christian; Wofsy, Steven; Wohlfahrt, Georg; Wolf, Sebastian; Woodgate, William; Li, Yuelin; Zampedri, Roberto; Zhang, Junhui; Zhou, Guoyi; Zona, Donatella; Agarwal, Deb; Biraud, Sebastien; Torn, Margaret; Papale, Dario (2020)
    The FLUXNET2015 dataset provides ecosystem-scale data on CO2, water, and energy exchange between the biosphere and the atmosphere, and other meteorological and biological measurements, from 212 sites around the globe (over 1500 site-years, up to and including year 2014). These sites, independently managed and operated, voluntarily contributed their data to create global datasets. Data were quality controlled and processed using uniform methods, to improve consistency and intercomparability across sites. The dataset is already being used in a number of applications, including ecophysiology studies, remote sensing studies, and development of ecosystem and Earth system models. FLUXNET2015 includes derived-data products, such as gap-filled time series, ecosystem respiration and photosynthetic uptake estimates, estimation of uncertainties, and metadata about the measurements, presented for the first time in this paper. In addition, 206 of these sites are for the first time distributed under a Creative Commons (CC-BY 4.0) license. This paper details this enhanced dataset and the processing methods, now made available as open-source codes, making the dataset more accessible, transparent, and reproducible.