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See detailAre BVOC exchanges in agricultural ecosystems overestimated? Insights from fluxes measured in a maize field over a whole growing season
Bachy, Aurélie ULg; Aubinet, Marc ULg; Schoon, Niels et al

in Atmospheric Chemistry and Physics (2016), 16(8),

Although maize is the second most important crop worldwide, and the most important C4 crop, no study on biogenic volatile organic compounds (BVOCs) has yet been conducted on this crop at ecosystem scale ... [more ▼]

Although maize is the second most important crop worldwide, and the most important C4 crop, no study on biogenic volatile organic compounds (BVOCs) has yet been conducted on this crop at ecosystem scale and over a whole growing season. This has led to large uncertainties in cropland BVOC emission estimations. This paper seeks to fill this gap by presenting, for the first time, BVOC fluxes measured in a maize field at ecosystem scale (using the disjunct eddy covariance by mass scanning technique) over a whole growing season in Belgium. The maize field emitted mainly methanol, although exchanges were bi-directional. The second most exchanged compound was acetic acid, which was taken up mainly in the growing season. Bi-directional exchanges of acetaldehyde, acetone and other oxygenated VOCs also occurred, whereas the terpenes, benzene and toluene exchanges were small, albeit significant. Surprisingly, BVOC exchanges were of the same order of magnitude on bare soil and on well developed vegetation, suggesting that soil is a major BVOC reservoir in agricultural ecosystems. Quantitatively, the maize BVOC emissions observed were lower than those reported in other maize, crops and grasses studies. The standard emission factors (SEFs) estimated in this study (231 ± 19 µg m−2 h−1 for methanol, 8 ± 5 µg m−2 h−1 for isoprene and 4 ± 6 µg m−2 h−1 for monoterpenes) were also much lower than those currently used by models for C4 crops, particularly for terpenes. These results suggest that maize fields are small BVOC exchangers in north-western Europe, with a lower BVOC emission impact than that modelled for growing C4 crops in this part of the world. They also reveal the high variability in BVOC exchanges across world regions for maize and suggest that SEFs should be estimated for each region separately. [less ▲]

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See detailImpact of tillage on CO2 and N2O efflux in an agricultural crop
Lognoul, Margaux ULg; Theodorakopoulos, Nicolas ULg; Hiel, Marie-Pierre ULg et al

Poster (2016, April 20)

CO2 and N2O fluxes exchanged by a maize crop were measured from June to Octboer 2015 using a homemade automated system of dynamic closed chambers. We studied the impact of tillage (reduced and ... [more ▼]

CO2 and N2O fluxes exchanged by a maize crop were measured from June to Octboer 2015 using a homemade automated system of dynamic closed chambers. We studied the impact of tillage (reduced and conventional) on greenhouse gas emissions and nitrous oxide flux dynamics. [less ▲]

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See detailAre BVOC exchanges in agricultural ecosystems overestimated? Insights from fluxes measured in a maize field over a whole growing season
Bachy, Aurélie ULg; Aubinet, Marc ULg; Schoon, Niels et al

Conference (2016, April 18)

This oral communication aims to present the main outputs of the BVOC (Biogenic Volatile Organic Compounds) flux measurement campaign performed on a maize field in Belgium. It begins by highligthing the ... [more ▼]

This oral communication aims to present the main outputs of the BVOC (Biogenic Volatile Organic Compounds) flux measurement campaign performed on a maize field in Belgium. It begins by highligthing the interest of investigating BVOC exchanges on maize; then measurement techniques are briefly presented. The second half of the communication aims to present and discuss the main outputs of this measurement campaign (similar BVOC composition, lower exchange rate than other maize and cropland/grassland studies, significant importance of soil in ecosystem exchanges, strong differences between exchanges rates observed in this study and those used by up-scaling models). [less ▲]

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See detailCanopy proximity estimation and impact on long term turbulent fluxes above a heterogeneous forest
Hurdebise, Quentin ULg; Vincke, Caroline; De Ligne, Anne ULg et al

Poster (2016, April 18)

With the development of eddy covariance networks like Fluxnet, ICOS or NEON, long-term data series of carbon dioxide, water vapor and other gas exchanges between terrestrial ecosystems and atmosphere will ... [more ▼]

With the development of eddy covariance networks like Fluxnet, ICOS or NEON, long-term data series of carbon dioxide, water vapor and other gas exchanges between terrestrial ecosystems and atmosphere will become more and more numerous. However, long-term analyses of such exchanges require a good understanding of measurement conditions during the investigated period. Independently of climate drivers, measurements may indeed be influenced by measurement conditions themselves subjected to long-term variability due to vegetation growth or set-up changes. The present research refers to the Vielsalm Terrestrial Observatory (VTO) where fluxes of momentum, carbon dioxide, latent and sensible heat have been continuously measured by eddy covariance during twenty years. VTO is an ICOS site installed in a mixed forest (beech, silver fir, Douglas fir, Norway spruce) in the Belgian Ardennes. A multidisciplinary approach was developed in order to investigate the spatial and temporal evolution of several site characteristics: - displacement height (d) and relative measurement height (z-d) were determined using a spectral approach that compared observed and theoretical cospectra; - turbulence statistics were analyzed in the context of Monin-Obukhov similarity theory; - tree height during the measurement period was obtained by combining tree height inventories, a LIDAR survey and tree growth models; - measurement footprint was determined by using a footprint model. A good agreement was found between the three first approaches. Results show notably that z-d was subjected to both temporal and spatial evolution. Temporal evolution resulted from continuous tree growth as well as from a tower raise, achieved in 2009. Spatial evolution, due to canopy heterogeneity, was also observed. The impacts of these changes on measurements are investigated. In particular, it was shown that they affect measurement footprint, flux spectral corrections and flux quality. All these effects must be taken into consideration in order to disentangle long-term flux evolutions due to climate or phenology from changes resulting from measurement set-up changes. [less ▲]

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See detailImpact of tillage on N2O and CO2 efflux in an agricultural crop
Lognoul, Margaux ULg; Theodorakopoulos, Nicolas ULg; Hiel, Marie-Pierre ULg et al

Poster (2016, April)

In an experiment conducted in the Belgian loess belt between June and October 2015, the effect of two tillage treatments (CT - conventional tillage and RT - reduced tillage) on CO2 and N2O fluxes ... [more ▼]

In an experiment conducted in the Belgian loess belt between June and October 2015, the effect of two tillage treatments (CT - conventional tillage and RT - reduced tillage) on CO2 and N2O fluxes exchanged by a maize crop were compared. Fluxes were measured using two fully automated sets of dynamic closed chambers, allowing a 4.5h temporal resolution. Soil water content and temperature were also monitored as well as pH, total N (TN) and total organic C (TOC) content. [less ▲]

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See detailLINKING CATTLE GRAZING BEHAVIOR TO METHANE AND CARBON DIOXIDE DYNAMICS
Blaise, Yannick ULg; Lebeau, Frédéric ULg; Andriamandroso, Andriamasinoro ULg et al

in Communications in Agricultural and Applied Biological Sciences (2016, February), 81(1), 107-112

Various methods are presently used to measure methane (CH4) emissions of ruminants on pasture. Those measurements are essential to evaluate nutritional strategies to mitigate enteric CH4 emissions as well ... [more ▼]

Various methods are presently used to measure methane (CH4) emissions of ruminants on pasture. Those measurements are essential to evaluate nutritional strategies to mitigate enteric CH4 emissions as well as addressing the selection of low producing individuals. On pasture and in the barn, variations in CH4 emissions are observed depending on the time of the day. However, no studies have been made to link these diurnal fluctuations to behavioural phases, especially on pasture. The aim of this study was to understand the individual dynamics of CH4 production and their links to the grazing behaviour. For this purpose, a new tool was specifically developed. Five red-pied dry cows were equipped with infrared CH4 and carbon dioxide (CO2) sensors measuring concentrations in the exhaled air at 4 Hz. The animals were equipped with a heart rate belt (HR) and motion sensors to detect their feeding behaviours (grazing vs. rumination) for periods of 8 h/d. Wind speed (WS) was also monitor to verify interference with sampled gas concentrations. Results showed that using the CH4:CO2 ratio reduced the interference with WS that was observed on raw CH4 and CO2 concentration signals. CH4:CO2 ratio average over 5 min periods indicated that CH4 emissions were lower during grazing than rumination (P<0.01). The eructation frequency during grazing (0.48 eructation/min, P<0.01) was also lower than during rumination (0.65 eructation/min). HR was higher during grazing that rumination. Because HR is usually linked to metabolic CO2 production intensity, hence influencing the denominator of the CH4:CO2 ratio, further investigation should focus on the quantification of changes in fermentative and metabolic CO2 emissions along the day to estimate total CH4 production more accurately and the relationship between CH4 emissions patterns and post-feeding times. [less ▲]

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See detailOUTDOOR MEASUREMENT OF CATTLE METHANE EMISSIONS USING THE EDDY-COVARIANCE TECHNIQUE IN COMBINATION WITH GEOLOCALIZATION DEVICES
Dumortier, Pierre ULg; Andriamandroso, Andriamasinoro ULg; Aubinet, Marc ULg et al

Poster (2016, February)

Methane emissions account for 8% of the EU-15 GHG emissions and livestock generates approximately half of these emissions [1]. In order to improve emissions reporting and properly test mitigation options ... [more ▼]

Methane emissions account for 8% of the EU-15 GHG emissions and livestock generates approximately half of these emissions [1]. In order to improve emissions reporting and properly test mitigation options, techniques for measuring methane emissions from cattle must be developed and adapted to each management system. Among available micrometeorological methods, the use of eddy-covariance is still in its infancy [2] and its relevance and robustness for cattle flux estimation has still to be proved. On one hand, it is well adapted to seasonal grazing systems, is non-invasive, needs little animal handling and allows detection of daily emission patterns. On the other hand, it has the drawback of requiring cattle geo-localization and long periods of measurements (typically one month). In this study, we combined measured CH4 fluxes with a footprint model [3] and cattle positions (GPS devices) over several one-month campaigns at key periods in the grazing season in order to obtain CH4 emissions per cow at herd scale. Accelerometers were also added to the system for behaviour detection, opening the possibility of linking emissions to feeding behaviour. Measurements were performed and are still ongoing at the Dorinne Terrestrial Observatory in 2014/2015. The first campaign provided a mean emission per cow of 65±6 kg CH4.LSU-1.year-1. Cattle emission pattern was tightly linked with behaviour pattern, emissions being higher during and shortly after grazing (i.e. at dawn and dusk). Uncertainties linked to the method will be discussed and quantified (footprint model validity, geo-localization precision, eddy covariance corrections and filtering specificities linked to CH4 measurements). Compilation of data from multiple campaigns will allow quantification of the effects of forage quality, animal weight and lactating state on emissions per cow. [less ▲]

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See detailUnexpected sensitivity of the annual net ecosystem exchange to the high frequency loss corrections in a grazed grassland site in Belgium
Mamadou, Ossénatou ULg; Gourlez de la Motte, Louis ULg; De Ligne, Anne ULg et al

Poster (2016)

The eddy covariance technique is widely used to measure CO2 and other gas fluxes. However, eddy covariance fluxes are affected by systematic errors that must be corrected. Among them, high frequency loss ... [more ▼]

The eddy covariance technique is widely used to measure CO2 and other gas fluxes. However, eddy covariance fluxes are affected by systematic errors that must be corrected. Among them, high frequency loss corrections are particularly important in this regard, especially when using a closed-path infrared gas analyzer. In this study, we compared three approaches to do these corrections for CO2 fluxes and evaluated their impact on the carbon balance an intensively grazed grassland site in Belgium . In the first approach, the computation of correction factors was based on the measured sensible heat cospectra (‘local’ cospectra), whereas the other two were based on theoretical models (Kaimal et al., 1972). The correction approaches were validated by comparing the nighttime eddy covariance CO2 fluxes corrected with each approach and in situ soil respiration measurements. We found that the local cospectra differed from the Kaimal theoretical shape, although the site could not be considered ‘difficult’ (i.e., fairly flat, homogeneous, low vegetation, sufficient measurement height), appearing less peaked in the inertial subrange. This difference greatly affected the correction factor, especially for night fluxes. Night fluxes measured by eddy covariance were found to be in good accord with in situ soil respiration measurements when corrected with local cospectra and to be overestimated when corrected with Kaimal cospectra. As the difference between correction factors was larger in stable than unstable conditions, this acts as a selective systematic error and has an important impact on annual fluxes. On the basis of a 4-year average, at DTO the errors reach 71-150 g C m-2 y-1 for net ecosystem exchange (NEE), 280-562 g C m-2 y-1 for total ecosystem respiration (TER) and 209-412 g C m-2 y-1 for gross primary productivity (GPP), depending on the approach used. We finally encourage site PIs to check the cospectrum shape at their sites and, if necessary, compute frequency correction factors on the basis of local cospectra rather than on Kaimal cospectra. [less ▲]

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See detailCarbon balance of an intensively grazed grassland in southern Belgium
Gourlez de la Motte, Louis ULg; Jérôme, Elisabeth; Mamadou, Ossénatou ULg et al

Poster (2016)

Grasslands are an important component of the global carbon balance but their carbon storage potential is still highly uncertain. Especially, the impact of weather variability and management practices on ... [more ▼]

Grasslands are an important component of the global carbon balance but their carbon storage potential is still highly uncertain. Especially, the impact of weather variability and management practices on grassland carbon budgets need to be assessed. This study investigates the carbon balance of an intensively managed permanent grassland in southern Belgium and its uncertainties by combining 5-years of eddy covariance measurements and other organic carbon exchanges estimates. The specificities of this study lie in: (i) the age of the pasture, which has probably been established since more than one century; (ii) the intensive character of the management with a mean grazing pressure larger than 2 livestock unit ha-1 and stocking cycle including stocking and rest periods, (iii) the livestock production system, typical of Wallonia, farming intensively Belgian Blue breed of cattle in order to produce meat. The results showed that, despite the high stocking rate and the old age of the pasture and the high stocking rate, the site acted as a relatively stable carbon sink from year to year with a 5-year average Net Biome Productivity of ‒173 [‒128 ‒203] g C m-2 yr-1. The carbon sink behavior of the pasture was directly increased by management practices through food complementation and organic fertilization and indirectly by mineral fertilization. The relatively low carbon budget inter-annual variability could be explained both by: (i) grazing management of the farmer that regulated Growth Primary Productivity by adapting the stocking rate to the Leaf Area Index which itself depends on weather conditions, (ii) carbon imports through food complements only when grass regrowth was not sufficient to feed the cattle. An exception occurred when low temperatures at the beginning of the year and a prolonged snow period provoked a delay in grass growth and therefore Growth Primary Productivity that could not be completely offset during the rest of the year. The results suggest that management practices that tend to optimize forage availability for meat production could contribute to maintaining a carbon sink. [less ▲]

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See detailPhénologie des hêtres dans une forêt ardennaise: comparaison de méthodes de suivi et relations avec les flux de CO2
Hurdebise, Quentin ULg; Vincke, Caroline; De Ligne, Anne ULg et al

Poster (2015, November 18)

Bien caractériser la phénologie des essences forestières dans un contexte climatique changeant est indispensable. Dans cette optique, confronter les différentes sources d’informations phénologiques ... [more ▼]

Bien caractériser la phénologie des essences forestières dans un contexte climatique changeant est indispensable. Dans cette optique, confronter les différentes sources d’informations phénologiques (relevé de terrain, modélisation, capteurs de rayonnement, caméra phénologique, satellite, eddy covariance…) est une démarche essentielle. Les différences et la complémentarité de ces sources d’informations ont été mises en évidence en utilisant les données provenant d’une forêt mixte de l’Est de la Belgique, principalement composée de hêtres. Par ailleurs, ces informations ont été utilisées pour étudier l’influence de la phénologie des hêtres sur les échanges annuels de CO2 de ces derniers. [less ▲]

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See detailInterpreting canopy development and physiology using a European phenology camera network at flux sites
Wingate, L.; Ogée, J.; Cremonese, E. et al

in Biogeosciences (2015), 12(10), 5995-6015

Plant phenological development is orchestrated through subtle changes in photoperiod, temperature, soil moisture and nutrient availability. Presently, the exact timing of plant development stages and ... [more ▼]

Plant phenological development is orchestrated through subtle changes in photoperiod, temperature, soil moisture and nutrient availability. Presently, the exact timing of plant development stages and their response to climate and management practices are crudely represented in land surface models. As visual observations of phenology are laborious, there is a need to supplement long-term observations with automated techniques such as those provided by digital repeat photography at high temporal and spatial resolution. We present the first synthesis from a growing observational network of digital cameras installed on towers across Europe above deciduous and evergreen forests, grasslands and croplands, where vegetation and atmosphere CO2 fluxes are measured continuously. Using colour indices from digital images and using piecewise regression analysis of time series, we explored whether key changes in canopy phenology could be detected automatically across different land use types in the network. The piecewise regression approach could capture the start and end of the growing season, in addition to identifying striking changes in colour signals caused by flowering and management practices such as mowing. Exploring the dates of green-up and senescence of deciduous forests extracted by the piecewise regression approach against dates estimated from visual observations, we found that these phenological events could be detected adequately (RMSE < 8 and 11 days for leaf out and leaf fall, respectively). We also investigated whether the seasonal patterns of red, green and blue colour fractions derived from digital images could be modelled mechanistically using the PROSAIL model parameterised with information of seasonal changes in canopy leaf area and leaf chlorophyll and carotenoid concentrations. From a model sensitivity analysis we found that variations in colour fractions, and in particular the late spring `green hump' observed repeatedly in deciduous broadleaf canopies across the network, are essentially dominated by changes in the respective pigment concentrations. Using the model we were able to explain why this spring maximum in green signal is often observed out of phase with the maximum period of canopy photosynthesis in ecosystems across Europe. Coupling such quasi-continuous digital records of canopy colours with co-located CO2 flux measurements will improve our understanding of how changes in growing season length are likely to shape the capacity of European ecosystems to sequester CO2 in the future. [less ▲]

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See detailSetting up an eddy covariance system to measure N2O fluxes exchanged by a production crop - First steps
Lognoul, Margaux ULg; SALERNO, Giovanni ULg; Debacq, Alain ULg et al

Poster (2015, October 20)

In order to study N2O exchanges by a Belgian production crop, we installed an eddy covariance system at the Terrestrial Observatory of Lonzée (Belgium), using a H2O and N2O quantum cascade laser analyzer ... [more ▼]

In order to study N2O exchanges by a Belgian production crop, we installed an eddy covariance system at the Terrestrial Observatory of Lonzée (Belgium), using a H2O and N2O quantum cascade laser analyzer and a sonic anemometer. We obtained three days of measurements and were able to investigate data preprocessing and flux calculation. We observed a drifting time-lag between the analyzer and the anemometers time series, presumably caused by an internal clock drift. Time-lag determination (using the covariance function maximum method) was more difficult for N2O than H2O, suggesting that this routine should be adapted to gas characterized by low fluxes. We investigated high frequency loss and found a system cut-off frequency of 0.5Hz for H2O, comparing its cospectrum to sensible heat cospectrum. We were not able to retrieve a neat cospectrum for N2O because of low fluxes during turbulent conditions. Further work and more data will be needed in order to bring answers to pending questions. [less ▲]

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See detailAir-sea ice gases exchange: update of recent findings, outcomes from sea ice models, caveats and open questions
Delille, Bruno ULg; Zhou, Jiayun; Kotovitch, Marie ULg et al

Conference (2015, September 21)

There are growing evidences that sea ice exchanges climate gases with the atmosphere. We will rapidly present a state of the art of current large scale assessment of spring and summer uptake of ... [more ▼]

There are growing evidences that sea ice exchanges climate gases with the atmosphere. We will rapidly present a state of the art of current large scale assessment of spring and summer uptake of atmospheric CO2. We will challenge these assessments with 1) new evidence of significant winter CO2 release for winter experiments 2) new finding of the role of bubbles formation and transport within sea ice and 3) impurities expulsion derived from combined artificial ice experiment and modelling. Finally, comparison of air-ice fluxes derived from automated chamber and micrometeorological method and, mechanistic and box models show significant discrepancies that suggest that the contribution of sea ice to the air-ocean fluxes of CO2 remain an open question. We will also highlight that sea ice contribute to the fluxes of other gases as CH4 ,N2O and DMS [less ▲]

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See detailYear Round Survey of Ocean-Sea Ice-Air Exchanges – the YROSIAE survey
Delille, Bruno ULg; Van Der Linden, Fanny ULg; Fripiat, François et al

Poster (2015, September 08)

YROSIAE survey aimed to carry out a year-round integrated survey of land-fast sea ice focusing on the study of sea ice physics and biogeochemistry in order to a) better understand and budget exchanges of ... [more ▼]

YROSIAE survey aimed to carry out a year-round integrated survey of land-fast sea ice focusing on the study of sea ice physics and biogeochemistry in order to a) better understand and budget exchanges of energy and matter across the ocean-sea ice-atmosphere interfaces during sea ice growth and decay and b) quantify their potential impact on fluxes of climate gases (CO2, DMS, CH4, N2O) to the atmosphere and on carbon and macro- nutrients and micro-nutrients export to the ocean. We will present the aims, overall approach and integrated sampling strategy of the YROSIAE survey. We will also discuss CO2 and N2O dynamics within sea ice. It appears that sea ice acts as a source of CO2 for the atmosphere in winter, counterbalancing spring sink. In addition, mineralization in spring appears to alleviate spring CO2 uptake. Intense nitrification in sea ice in spring fosters emission of N2O at the air-ice interface. [less ▲]

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See detailAn ecosystem-scale perspective of the net land methanol flux: synthesis of micrometeorological flux measurements
Wohlfahrt, G.; Amelynck, C.; Ammann, C. et al

in Atmospheric Chemistry and Physics (2015), (15), 7413-7427

Methanol is the second most abundant volatile organic compound in the troposphere and plays a significant role in atmospheric chemistry. While there is consensus about the dominant role of living plants ... [more ▼]

Methanol is the second most abundant volatile organic compound in the troposphere and plays a significant role in atmospheric chemistry. While there is consensus about the dominant role of living plants as the major source and the reaction with OH as the major sink of methanol, global methanol budgets diverge considerably in terms of source/sink estimates, reflecting uncertainties in the approaches used to model and the empirical data used to separately constrain these terms. Here we compiled micrometeorological methanol flux data from eight different study sites and reviewed the corresponding literature in order to provide a first cross-site synthesis of the terrestrial ecosystem-scale methanol exchange and present an independent data-driven view of the land–atmosphere methanol exchange. Our study shows that the controls of plant growth on production, and thus the methanol emission magnitude, as well as stomatal conductance on the hourly methanol emission variability, established at the leaf level, hold across sites at the ecosystem level. Unequivocal evidence for bi-directional methanol exchange at the ecosystem scale is presented. Deposition, which at some sites even exceeds methanol emissions, represents an emerging feature of ecosystem-scale measurements and is likely related to environmental factors favouring the formation of surface wetness. Methanol may adsorb to or dissolve in this surface water and eventually be chemically or biologically removed from it. Management activities in agriculture and forestry are shown to increase local methanol emission by orders of magnitude; however, they are neglected at present in global budgets. While contemporary net land methanol budgets are overall consistent with the grand mean of the micrometeorological methanol flux measurements, we caution that the present approach of simulating methanol emission and deposition separately is prone to opposing systematic errors and does not allow for full advantage to be taken of the rich information content of micrometeorological flux measurements. [less ▲]

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See detailCritical periods and critical values explaining fluxes inter-annual variability in a temperate mixed forest
Hurdebise, Quentin ULg; Vincke, Caroline; De Ligne, Anne ULg et al

Poster (2015, June 04)

In order to explain inter-annual variability of Net Ecosystem CO2 Exchange (NEE) above a mixed temperate forest, two approaches were followed: •Detection of critical periods using the R-squared of the ... [more ▼]

In order to explain inter-annual variability of Net Ecosystem CO2 Exchange (NEE) above a mixed temperate forest, two approaches were followed: •Detection of critical periods using the R-squared of the regression between annual NEE and cumulated NEE on a mobile window. •Identification of critical values of a threshold used to decompose annual and seasonal NEE in two components. [less ▲]

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See detailThe CROSTVOC project – an integrated approach to study the effect of stress on BVOC exchange between agricultural crops and grassland ecosystems and the atmosphere
Amelynck, Crist; Heinesch, Bernard ULg; Aubinet, Marc ULg et al

in Geophysical Research Abstracts (2015, April), 17

Global changes in atmospheric composition and climate are expected to affect BVOC exchange between terrestrial vegetation and the atmosphere through changes in the drivers of constitutive BVOC emissions ... [more ▼]

Global changes in atmospheric composition and climate are expected to affect BVOC exchange between terrestrial vegetation and the atmosphere through changes in the drivers of constitutive BVOC emissions and by increases in frequency and intensity of biotic or abiotic stress episodes. Indeed, several studies indicate changes in the emission patterns of constitutive BVOCs and emission of stress-induced BVOCs following heat, drought and oxidative stress, amongst others. Relating changes in BVOC emissions to the occurrence of one or multiple stressors in natural environmental conditions is not straightforward and only few field studies have dealt with it, especially for agricultural crop and grassland ecosystems. The CROSTVOC project aims to contribute in filling this knowledge gap in three ways. Firstly, it aims at performing long-term BVOC emission field measurements from maize (Zea mays L.) and wheat (Triticum aestivum L.), two important crop species on the global scale, and from grassland. This should lead to a better characterization of (mainly oxygenated) BVOC emissions from these understudied ecosystems, allowing a better representation of those emissions in air quality and atmospheric chemistry and transport models. BVOC fluxes are obtained by the Disjunct Eddy Covariance by mass scanning (DEC-MS) technique, using a hs-PTR-MS instrument for BVOC analysis. Secondly, the eddy covariance BVOC flux measurements (especially at the grassland site) will be accompanied by ozone flux, chlorophyll fluorescence, photosynthesis and soil moisture measurements, amongst others, to allow linking alterations in BVOC emissions to stress episodes. Simultaneously, automated dynamic enclosures will be deployed in order to detect specific abiotic and biotic stress markers by PTR-MS and identify them unambiguously by GC-MS. Thirdly, the field measurements will be accompanied by laboratory BVOC flux measurements in an environmental chamber in order to better disentangle the responses of the BVOC emissions to driving factors that co-occur in field conditions and to determine the influence of single abiotic stressors on BVOC emissions. Next to a general presentation, some preliminary results of the project will be shown. [less ▲]

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