Publications of Marc Aubinet
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See detailIRGA GAS SAMPLING SYSTEM DIMENSIONING: LABORATORY AND FIELD EXPERIMENTS
De Ligne, Anne ULg; Joly, Lilian; Cousin, Julien et al

Poster (2014, September 23)

The gas sampling system (GSS), which carries air from the sampling point to the IRGA, is an essential component of the eddy covariance system. It has to meet several constraints, among which minimizing ... [more ▼]

The gas sampling system (GSS), which carries air from the sampling point to the IRGA, is an essential component of the eddy covariance system. It has to meet several constraints, among which minimizing high frequency attenuation of concentration measurement and keeping pressure drop in the measurement cell in an acceptable range. Rain cup, filters, tubes and pumps are key elements of this system and need proper dimensioning. The elaboration of the ICOS protocol for IRGA required such dimensioning and optimization. Laboratory and field measurements were carried out with this aim. In the laboratory, a dynamic calibration bench was developed to investigate experimentally the pressure drop and the concentration fluctuation attenuation caused by different filters. In the field, three LI-7200 equipped with different GSS were installed and run at the Dorinne Terrestrial Observatory (ICOS-Belgium). Main experiment conclusions were that: • The shape and size of the rain cup has a critical impact on cut off frequencies • The filter porosity and size has a critical impact on pressure drop • Filter heating is necessary in order to avoid condensation and filter blocking These experiments led to the definition of the GSS functioning range that is finally proposed in the ICOS IRGA protocol. [less ▲]

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See detailAre agricultural ecosystems important BVOC « exchangers »? Evidences from 2 measurement years on croplands at Lonzée (Belgium)
Bachy, Aurélie ULg; Aubinet, Marc ULg; Schoon, Niels et al

Poster (2014, July 01)

For the last decades, agricultural ecosystems have been a key biome for diverse socio-economical, environmental and climatic issues. And one of these climatic issues is just BVOC (Biogenic Volatile ... [more ▼]

For the last decades, agricultural ecosystems have been a key biome for diverse socio-economical, environmental and climatic issues. And one of these climatic issues is just BVOC (Biogenic Volatile Organic Compounds) emission from terrestrial ecosystems. Indeed, those compounds which are mostly emitted by plants play a great role in the atmospheric chemistry, thereby influencing the Earth surface radiative budget and the tropospheric air quality. However, so far, very few is known about BVOC exchange by crops, implying that huge uncertainties remain about qualifying, quantifying and determining sources/sinks and driving mechanisms of BVOC exchanges between croplands ecosystems and the atmosphere. We present here the first long term BVOC fluxes measurement study conducted on maize (2012) and winter wheat (2013), respectively the second and first most important worldwide crops (FAOSTAT). BVOC exchange was measured using the disjunct by mass scanning eddy covariance technique (+ PTR-MS, Ionicon) at the Lonzée Terrestrial Observatory (ICOS site) in Belgium. Main results are: (i) crops emit mainly methanol; (ii) BVOC fluxes from studied crops is lower than in literature, suggesting that agricultural ecosystems are poor BVOC exchangers; (iii) soil is a significant BVOC source. [less ▲]

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See detailImpact of abiotic stresses on volatile organic compound production of field crops and grasslands
Digrado, Anthony ULg; Mozaffar, Ahsan ULg; Bachy, Aurélie ULg et al

Poster (2014, February 07)

Abiotic and biotic stresses are known to alter biogenic volatile organic compound (BVOC) emission from plants. With the climate and global change, BVOC emissions are likely to increase. This increase on ... [more ▼]

Abiotic and biotic stresses are known to alter biogenic volatile organic compound (BVOC) emission from plants. With the climate and global change, BVOC emissions are likely to increase. This increase on BVOC emissions could be driven by many environmental parameters like temperature, ozone and light availability for photosynthesis although it is still difficult to predict the impact of some environmental parameters, environmental controls on BVOC emission being species and BVOC-dependent. These BVOC are involved in a wide range of interactions of plants with their environment and these interactions could be affected by the global change. Moreover, BVOC also play a key role in the atmospheric chemistry and may contribute to ozone formation and an increase in methane lifetime, strengthening the global change. Yet, due to technical limitation, there are few studies examining the impact of multiple co-occurring stresses on BVOC emission at the ecosystem level although stress combination is probably more ecologically realistic in field. In the CROSTVOC (for CROp STress VOC) project, the impact of abiotic stresses (e.g. heat, drought, ozone and grazing) on BVOC emission will be investigated for field crops (maize and wheat) and grassland both at the ecosystem and plant scale. [less ▲]

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See detailMEASUREMENT OF CATTLE METHANE EMISSIONS USING THE EDDY-COVARIANCE TECHNIQUE
Dumortier, Pierre ULg; Aubinet, Marc ULg; Debacq, Alain ULg et al

Poster (2014)

Methane emissions account for 8% of the EU-15 GHG emissions and livestock generates approximately half of these emissions [1]. Recent technological advances in spectroscopy now permit methane flux ... [more ▼]

Methane emissions account for 8% of the EU-15 GHG emissions and livestock generates approximately half of these emissions [1]. Recent technological advances in spectroscopy now permit methane flux measurement using eddy covariance. Methane fluxes exchanged by a pasture were measured continuously since June 2012 at the Dorinne Terrestrial Observatory in Belgium. During grazing periods, fluxes are dominated by enteric fermentation. Methane emissions were found strongly related to cattle stocking rate. When fluxes are integrated over large periods and assuming a random position of cows on the pasture, emission per LSU (Livestock Unit) was found to be 53±3 kg CH4 year-1 LSU-1. Recently, cattle position on the grassland was monitored continuously using GPS devices and combined with a footprint analysis [2] to derive more precisely the CH4 emission per LSU. A first experiment with a stocking rate close to 0.7 LSU ha-1 validated the approach and ended in a mean emission per head of 51±10 kg CH4 year-1 head-1. This approach also allows estimating emissions per head at the hourly scale and therefore opens the possibility of studying the circadian emission cycle and to link emissions to feeding behavior of the animal and feed quality. [less ▲]

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See detailYearly Follow-up of Methane Turbulent Exchange Over an Intensively Grazed Pasture in Belgium
Dumortier, Pierre ULg; Aubinet, Marc ULg; Beckers, Yves ULg et al

in Communications in Agricultural and Applied Biological Sciences (2014), 79(1), 91-96

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See detailEtablissement du bilan de carbone d’une exploitation agricole wallonne pratiquant le système allaitant : effets du climat et de la gestion du pâturage. Rapport de synthèse. Janvier 2012 – Décembre 2013.
Jerome, Elisabeth ULg; Dumortier, Pierre ULg; Beckers, Yves ULg et al

Report (2013)

Dans l’optique d’une atténuation des émissions de Gaz à Effet de Serre (GES) des systèmes d’élevage, les écosystèmes prairiaux peuvent jouer un rôle important vu leur potentiel de séquestration de carbone ... [more ▼]

Dans l’optique d’une atténuation des émissions de Gaz à Effet de Serre (GES) des systèmes d’élevage, les écosystèmes prairiaux peuvent jouer un rôle important vu leur potentiel de séquestration de carbone (C) dans les sols. Une évaluation pertinente de la contribution des systèmes d’élevage herbivores aux émissions de GES nécessite de raisonner en termes de bilan, en considérant à la fois les sources de GES et leur compensation via la séquestration de carbone par les prairies. Le projet « Etablissement du bilan de carbone d’une exploitation agricole wallonne pratiquant le système allaitant : effets du climat et de la gestion du pâturage » a pour objectif d’établir un inventaire de la contribution nette des systèmes d’élevage en Wallonie aux flux de GES (CO2, N2O, CH4). A long terme, nous étudierons les possibilités de réduction de ces émissions nettes par des adaptations des modes de conduite des systèmes d’élevage en adéquation avec leurs objectifs économiques et sociaux. L’exploitation étudiée est une exploitation agricole du type « naisseur-éleveur ». L’élevage se compose de vaches allaitantes et des veaux non sevrés de l’année de race « Blanc Bleu Belge culard ». Le système d’alimentation se base essentiellement sur la prairie permanente durant la période estivale et les produits conservés de la prairie durant la période hivernale. Ce rapport constitue l’état d’avancement du projet au terme de la deuxième biennale. [less ▲]

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See detailFifty years of crop residue management have a limited impact on soil heterotrophic respiration.
Buysse, Pauline ULg; Schnepf-Kiss, Anne-Caroline; Carnol, Monique ULg et al

in Agricultural and Forest Meteorology (2013), 180

The impacts of crop residue management on soil microbial biomass, labile carbon and heterotrophic respiration (HR) were assessed at a long-term experimental site in the Hesbaye region in Belgium. Three ... [more ▼]

The impacts of crop residue management on soil microbial biomass, labile carbon and heterotrophic respiration (HR) were assessed at a long-term experimental site in the Hesbaye region in Belgium. Three treatments, residue export (RE), farmyard manure addition (FYM) and residue restitution after harvest (RR), have been applied continuously since 1959. The soil is a Eutric Cambisol with, in 2010, significantly different total soil organic carbon contents of 4.4, 5.1 and 5.9 kg C m-2 under the RE, RR and FYM treatments, respectively. Manual field HR measurements were carried out during the 2010 and 2012 crop seasons using a dynamic closed chamber system. Microbial biomass, labile C content and metabolic diversity of soil bacteria were assessed in spring 2012. Fifty-one years after the beginning of the treatments, residue management had a limited impact on HR. Based on daily averaged values, the treatment had a significant impact (α = 10%) in 2012 but not in 2010. Based on the individual measurement dates, the treatment impact was less obvious in 2012; with the observation of a significant impact (α = 10%) on HR in only 7% and 36.8% of the measurement dates in 2010 and 2012, respectively. Labile C and microbial biomass were significantly lower in the RE treatment than in FYM and RR. Residue management had no significant effect on cold-water extracted carbon and metabolic diversity of heterotrophic soil bacteria. The limited impact of residue management on HR could be explained by (i) the relatively low amounts of recent above-ground crop inputs, (ii) the large proportion of below-ground residues and other non-exportable above-ground residues reducing the potential differences between treatments and (iii) the relatively large spatial variability of HR. In conclusion, carbon losses due to heterotrophic respiration did not differ between RE, FYM and RR treatments in the studied soil. This contrasts with the different soil organic carbon contents observed in these three treatments after fifty years of experiment. Further investigations regarding the reduction of spatial variability and the potential roles played by organic matter protection within aggregates and biochemical composition of inputs are needed. [less ▲]

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See detailNitrous oxide emissions using quantum cascade laser spectrometry over a production crop: preliminary results
SALERNO, Giovanni ULg; Aubinet, Marc ULg; Joly, Joly et al

Poster (2013, September 18)

Amongst the greenhouse gases, nitrous oxide is recognized as having the greatest greenhouse forcing potential and as being the third in terms of radiative forcing. Agriculture is known to be the major ... [more ▼]

Amongst the greenhouse gases, nitrous oxide is recognized as having the greatest greenhouse forcing potential and as being the third in terms of radiative forcing. Agriculture is known to be the major anthropic emitter. This work is part of the FERTECOL project and its objective is to measure the emissions of nitrous oxide by a production crop with an eddy covariance system. The measurements extent over the growth period, cover a large range of climatic conditions and capture peak events associated with fertilization. The measurements, started in April 2013, are carried at the Lonzée Terrestrial Observatory (50°33'5.83"N- 4°44'46.22"E). On this year, the crop is planted with winter wheat. A Quantum Cascade Laser Absorption Spectrometer (QCLAS, GSMA, France) is used to measure nitrous oxide as well as water vapor and carbon dioxide at a frequency of 5 hertz. The fluxes are computed using the Eddy Covariance technique adapting standards quality and corrections procedures set up for CO2 fluxes to N2O. Standard meteorological measurements are performed in parallel. The analysis will present response of the fluxes to environmental variables as well as to fertilization events during the season. [less ▲]

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See detailImpact of grazing on carbon dioxide flux exchanges in an intensively managed grassland
Jerome, Elisabeth ULg; Beckers, Yves ULg; Bodson, Bernard ULg et al

Poster (2013, September)

To date, there are few studies assessing the impact of specific management events, particularly grazing, on carbon (C) and carbon dioxide (CO2) fluxes in managed grasslands. Grazing effects are indeed ... [more ▼]

To date, there are few studies assessing the impact of specific management events, particularly grazing, on carbon (C) and carbon dioxide (CO2) fluxes in managed grasslands. Grazing effects are indeed difficult to discern. They vary with the stocking rate and the length of the grazing period. Moreover, they are often masked by environmental responses. The aim of the present study was to assess the impact of grazing on the CO2 fluxes of a grassland grazed by the Belgian Blue breed of cattle. The research was run at the Dorinne Terrestrial Observatory (DTO), located in the Belgian Condroz (50° 18’ 44’’ N; 4° 58’ 07’’ E; 248 m asl.). The site is a permanent grassland of ca. 4.2 ha subjected to intensive management. Grassland carbon budget at the system boundaries is calculated from Net Ecosystem Exchange of CO2 measured by eddy covariance by taking imports and exports of organic C and losses of carbon as methane into account. After 2 years of measurements, the site was close to equilibrium. If management practices (harvest, fertilization and imports as supplementary feedings) and climatic conditions had a significant impact on the C balance, the impact of grazing was uncertain, especially on CO2 fluxes. To do this analysis, we distinguished the long term and the short term impacts of grazing on CO2 fluxes. The long term effect results from the biomass consummation by the cattle and from the cattle effluents that modify assimilation and respiration fluxes. This could be quantified only by comparing fluxes before and after grazing periods. The short term impact is due to cattle respiration that is a part of total ecosystem respiration and should be measured in its presence in the field. For the long term effects of grazing on CO2 fluxes, we analyzed the temporal evolution of gross maximal photosynthetic capacity GPPmax and dark respiration normalized at 10°C (Rd,10). Those parameters were deduced from the response of daytime CO2 fluxes to radiation over 5-day windows. We calculated parameters variations between the beginning and the end of grazing and non-grazing periods (∆GPPmax, ∆Rd,10) and analyzed their dependence to stocking rate. We found a significant decreased of ∆GPPmax that allowed us to quantify the assimilation reduction due to grass consumption by cattle. Discrimination of this impact from flux response to climate was possible only after gathering and treating two years of measurements taken under various climatic conditions. At the opposite, no significant evolution of Rd,10 with the average stocking rate was found. The short term impacts were an increase of CO2 fluxes in presence of cattle. It could be distinguished and quantified only thanks to confinement experiments. Each experiment extended over two days: the first day, cattle was confined in the footprint of the eddy covariance set-up (1.76 ha, 27 LU ha-1) and the second day, it was removed from it. We compared filtered half-hourly data made at 24h intervals, in the presence or absence of cattle, considering that environmental conditions were equivalent (air temperature, wind speed, radiation and wind direction). Livestock contribution to CO2 fluxes was estimated to be 2.25 ± 0.68 kg C LU-1 d-1. [less ▲]

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See detailCattle methane fluxes measurement over an intensively grazed grassland using eddy covariance
Dumortier, Pierre ULg; Aubinet, Marc ULg; Beckers, Yves ULg et al

Poster (2013, September)

Methane emissions account for 8% of the EU-15 GHG emissions and livestock generates approximately half of these emissions (European Commission, 2009). Recent technological advances in spectroscopy now ... [more ▼]

Methane emissions account for 8% of the EU-15 GHG emissions and livestock generates approximately half of these emissions (European Commission, 2009). Recent technological advances in spectroscopy now permit methane flux measurement using eddy covariance. This method has numerous strengths. It can measure fluxes in situ, continuously and across broad areas. This provides information about meadow and cattle emission behaviour throughout the year and across a broad range of climatic conditions. We will present here a one year monitoring of methane exchange between an intensively grazed meadow and the atmosphere obtained using the eddy-covariance method. Methane fluxes exchanged by a grazed meadow were measured continuously since June 2012 at the Dorinne Terrestrial Observatory (50˚ 18’ 44” N; 4˚ 58’ 07” E; 248 m asl.) in Belgium. The site is an intensively pastured meadow of 4.2 ha managed according to the regional common practices where up to 30 Belgian Blue cows are grazing simultaneously. Flux measurements were made with the eddy covariance technique, using a fast CH4 analyzer (Picarro G2311-f) and a sonic anemometer (Campbell Csat3). Carbon dioxide fluxes and various micro-meteorological and soil variables, biomass growth and stocking rate evolution were also measured at the site. Turbulent fluxes were calculated according to standard eddy covariance computation schemes and were filtered for non-stationarity and for low friction velocity (u*) events. During grazing periods, fluxes are dominated by the enteric fermentation source and average 111 nmol m-2 s-1. They are highly variable, probably due to cow movements in and out the measurement footprint and cow digestion rhythm. Despite this spread, a daily emission rhythm is observed with higher emissions during the afternoon. When fluxes are integrated over large periods, methane emissions were found strongly related to cattle stocking rate with a slope of 7.34±0.78 mol CH4 day-1 LSU-1. Further developments are ongoing in order to improve cattle geo-localization through infra-red cameras and individual home-made GPS devices. The two systems will be compared in terms of cost, efficiency and ease of use. During cow-free periods, the methane flux averages 10.5 nmol m-2 s-1 and is highly variable with some production peaks above 100 nmol m-2 s-1. No relation was found between methane fluxes and soil temperature while a weak negative relation was found between methane fluxes and soil humidity. No soil methane absorption has been observed. European Commission. Fifth National Communication from the European Community Under the UN Framework Convention on Climate Change (UNFCCC). Technical Report - 2009 – 038 (2009). [less ▲]

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See detailMesures des flux in situ de gaz à effet de serre (N2O, CO2, H2O …) avec la station ECoFlux (Eddy Covariance Flux
Joly, Lilian; Decarpenterie, Thomas; Dumelié, Nicolas et al

Conference given outside the academic context (2013)

La concentration atmosphérique en gaz à effet de serre, responsable du réchauffement du climat, ne cesse d'augmenter depuis le début de l'ère industrielle. Les hypothèses médianes du groupe international ... [more ▼]

La concentration atmosphérique en gaz à effet de serre, responsable du réchauffement du climat, ne cesse d'augmenter depuis le début de l'ère industrielle. Les hypothèses médianes du groupe international d'experts sur le changement climatique (IPCC) prédisent un doublement de la concentration en dioxyde de carbone (CO2) avant la fin de ce siècle. De plus, la concentration d'autres gaz à effet de serre au pouvoir radiatif supérieur à celui du CO2 augmente, comme par exemple le méthane (CH4) et le protoxyde d’azote (N2O). Le N2O présente un potentiel de réchauffement d’environ 310 fois plus élevé que celui du CO2 avec une durée de vie de 120 à 150 ans. Son augmentation actuelle de 0.3% par an de sa concentration est imputable à l’activité anthropique incluant des processus industriels via l’utilisation de solvants mais surtout aux activités agricoles pour environ 70% via des processus biologiques de nitrification et dénitrification se produisant dans les sols. Afin de mieux comprendre l’effet des pratiques agricoles sur les échanges gazeux entre les sols et l’atmosphère, il faut quantifier les flux réels en fonction des différents types de sols, de pratiques culturales, de climats et d’écosystèmes. La limite actuelle de mesure de ces flux (notamment pour le N2O) réside dans la mauvaise sensibilité et stabilité des instruments de mesure en conditions de terrain. Depuis peu le GSMA (Groupe de Spectroscopie Moléculaire et Atmosphérique) a mis au point une station nommée ECoFlux (Eddy Covariance Flux) utilisant un senseur innovant reposant sur la spectrométrie laser infrarouge. Il permet de déterminer simultanément les flux in situ de N2O, CO2 et H2O par la méthode de covariance. Après une présentation du principe de la station ECoFlux, nous exposerons les résultats de deux campagnes de mesure sur des sites « grandes cultures » de suivi de gaz à effet de serre appartenant au réseau ICOS (http://www.icos-infrastructure.eu/). Nous terminerons en développant les intérêts et les modalités du déploiement de cette station sur site viticole [less ▲]

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See detailVertical canopy gradient in photosynthesis and monoterpenoid emissions: An insight into the chemistry and physiology behind
Simpraga, M.; Verbeeck, H.; Bloemen, J. et al

in Atmospheric Environment (2013), 80

It is well known that vertical canopy gradients and varying sky conditions influence photosynthesis (Pn), specific leaf area (SLA), leaf thickness (LT) and leaf pigments (lutein, â-carotene and ... [more ▼]

It is well known that vertical canopy gradients and varying sky conditions influence photosynthesis (Pn), specific leaf area (SLA), leaf thickness (LT) and leaf pigments (lutein, â-carotene and chlorophyll). In contrast, little is known about these effects on monoterpenoid (MT) emissions. Our study examines simultaneously measured Pn, MT emissions and the MT/Pn ratio along the canopy of an adult European beech tree (Fagus sylvatica L.) in natural forest conditions. Dynamic branch enclosure systems were used at four heights in the canopy (7, 14, 21 and 25 m) in order to establish relationships and better understand the interaction between Pn and MT emissions under both sunny and cloudy sky conditions. Clear differences in Pn, MT emissions and the MT/Pn ratio were detected within the canopy. The highest Pn rates were observed in the sun leaves at 25 m due to the higher intercepted light levels, whereas MT emissions (and the MT/Pn ratio) were unexpectedly highest in the semi-shaded leaves at 21 m. The higher Pn rates and, apparently contradictory, lower MT emissions in the sun leaves may be explained by the hypothesis of Owen and Peñuelas (2005), stating synthesis of more photo-protective carotenoids may decrease the emissions of volatile isoprenoids (including MTs) because they both share the same biochemical precursors. In addition, leaf traits like SLA, LT and leaf pigments clearly differed with height in the canopy, suggesting that the leaf’s physiological status cannot be neglected in future research on biogenic volatile organic compounds (BVOCs) when aiming at developing new and/or improved emission algorithms. [less ▲]

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See detailLong term measurements of VOC exchanges above a maize field at Lonzée (Belgium)
Bachy, Aurélie ULg; Aubinet, Marc ULg; SALERNO, Giovanni ULg et al

Poster (2013, June 10)

For the last decades, VOC had arisen scientifict interest due to their important role in the atmospheric chemistry and their final impact on air pollution and climate change. Terrestrial ecosystems being ... [more ▼]

For the last decades, VOC had arisen scientifict interest due to their important role in the atmospheric chemistry and their final impact on air pollution and climate change. Terrestrial ecosystems being the main VOC source, evaluation of current and future biogenic VOC emissions through VOC exchange modeling is thus necessary to better estimate future climate and assess future air pollution risks. BVOC exchanges depend on edaphic variables and are plant species specific. Therefore, their modeling and global budget evaluation requires a comprehensive understanding of production and exchange dynamics under a wide panel of climatic conditions and ecosystems, which necesserily implies BVOC exchange measurements under varied conditions. In that perspective, forest and non pastured grasslands have been largely studied for the last decade, but knowledge about BVOC fluxes from croplands remains still scarce. As a consequence, crop species-specific standard emissions that feed bottom-up BVOC emission models are still often assigned to a default value that is in addition kept constant for the entire growth season, although recent research has shown that plant phenology, acclimation and stress can drastically influence BVOC emissions. To help filling this knowledge gap, we run a project that aims to study VOC fluxes from two major croplands, maize (2nd most important culture worldwide) and winter wheat (1st most important culture worldwide), and a pastured grassland. We present here a specific study focussing on the VOC exchanges between a maize field and the atmosphere. VOC fluxes were measured at ecosystem-scale during the whole 2012 growing season using the eddy covariance by mass-scaning technique with a proton-transfer-reaction mass spectrometer. Together with VOC fluxes, we also recorded a wide set of ancillary data including CO2 fluxes, meteorological variables and biomass evolution. As far as we know, we are the first study dealing with BVOC measurements on maize at ecosystem scale and spanning all the phenological stages of the crop. Although first results show half-hourly bidirectionnal exchanges among all the preselected compounds, in average methanol is the greatest emitted VOC, followed by green leaf volatiles. Acetic acid and acetaldehyde are the greatest taken up VOC. Small isoprene and monoterpene fluxes are also observed. A diurnal pattern is found for all those VOC, with greater emission/uptake during the day, suggesting a flux dependence on environmental parameters. Influence of environmental controls, biomass evolution (including growth primary production) and phenology on fluxes is currently under investigation. Our research allows to quantify BVOC exchanges by a maize field throughout a whole growing season. Hence, obtained results will refine the understanding of the BVOC exchanges mechanisms by including both environmental and phenological parameters. Such results are expected to be very useful for BVOC modeling, especially for oxygenated compounds such as methanol. [less ▲]

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See detailEvapotranspiration amplifies European summer drought
Teuling, Adriaan J.; Van Loon, Anne F.; Seneviratne, Sonia Isabelle et al

in Geophysical Research Letters (2013)

Drought is typically associated with a lack of precipitation, whereas the contribution of evapotranspiration and runoff to drought evolution is not well understood. Here, we use unique long-term ... [more ▼]

Drought is typically associated with a lack of precipitation, whereas the contribution of evapotranspiration and runoff to drought evolution is not well understood. Here, we use unique long-term observations made in four headwater catchments in Central and Western Europe to reconstruct storage anomalies and study the drivers of storage anomaly evolution during drought. We provide observational evidence for the ‘drought-paradox’ in that region: a consistent and significant increase in evapotranspiration during drought episodes which acts to amplify the storage anomalies. In contrast, decreases in runoff act to limit storage anomalies. Our findings stress the need for the correct representation of evapotranspiration and runoff processes in drought indices. [less ▲]

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See detailImpact of diffuse light on isoprene and monoterpene emissions from a mixed temperate forest
Laffineur, Quentin ULg; Aubinet, Marc ULg; Schoon, Niels et al

in Atmospheric Environment (2013), 46(74), 385-392

This study investigated the impact of diffuse light on canopy scale emission of isoprene and monoterpenes measured continuously above a mixed temperate forest, using the disjunct eddy-covariance by mass ... [more ▼]

This study investigated the impact of diffuse light on canopy scale emission of isoprene and monoterpenes measured continuously above a mixed temperate forest, using the disjunct eddy-covariance by mass scanning technique with a proton transfer reaction-mass spectrometer (PTR-MS) instrument. To assess this impact, the relationship between emissions/radiation and emissions/gross primary production (GPP) under clear sky and cloudy conditions were analysed. Under cloudy conditions (high proportion of diffuse radiation), the isoprene and monoterpene fluxes were enhanced compared to clear sky conditions (low proportion of diffuse radiation) at equivalent temperature and above-canopy total radiation. The whole-canopy enzymatic activity of the metabolic isoprene production pathway, however, was suggested to be lower under cloudy conditions than under clear sky conditions at equivalent temperature. The mechanisms behind these observations are probably linked to the better penetration of diffuse radiation in the canopy. Shade leaves/needles receive more radiation in cloudy conditions than in clear sky conditions, thereby inducing the observed effects. [less ▲]

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See detailImpact of grazing on carbon balance of an intensively grazed grassland in Belgium
Jerome, Elisabeth ULg; Beckers, Yves ULg; Beekkerk van Ruth, Jöran ULg et al

Poster (2013, April 09)

This work analyzes the impact of grazing on the carbon balance of a grassland grazed by the Belgian Blue breed of cattle. The research was run at the Dorinne terrestrial observatory (DTO). The ... [more ▼]

This work analyzes the impact of grazing on the carbon balance of a grassland grazed by the Belgian Blue breed of cattle. The research was run at the Dorinne terrestrial observatory (DTO). The experimental site is a permanent grassland of ca. 4.2 ha located in the Belgian Condroz (50° 18’ 44’’ N; 4° 58’ 07’’ E; 248 m asl.). Other studies are conducted at the DTO including measurements of methane (CH4) and nitrous oxide fluxes (Dumortier et al., Geophysical Research Abstracts, Vol. 15, EGU2013-2083-1, 2013; Beekkerk van Ruth et al., Geophysical Research Abstracts, Vol. 15, EGU2013-3211, 2013, respectively). Grassland carbon budget (Net Biome Productivity, NBP) was calculated from Net Ecosystem Exchange (NEE) measured by eddy covariance by taking imports and exports of organic C and losses of carbon as CH4 into account (Soussana et al., 2010). After 2 years of measurements (May 2010 - May 2012), the grassland behaved on average as a CO2 source (NEE = 73 ±31 g C m-2 y-1). After inclusion of all the C inputs and outputs the site was closed to equilibrium (NBP = 23 ±34 g C m-2 y-1). To analyze the impact of grazing on CO2 fluxes, we studied the temporal evolution of gross maximal photosynthetic capacity GPPmax and dark respiration Rd (deduced from the response of daytime fluxes to radiation over 5-day windows). We calculated GPPmax and Rd variation between the end and the beginning of grazing or non-grazing periods (∆GPPmax and ∆Rd, respectively). We observed a significant decrease of GPPmax during grazing periods and measured a ∆GPPmax dependence on the average stocking rate. This allows us to quantify the assimilation reduction due to grass consumption by cattle. On the contrary, no Rd decrease was observed during grazing periods. Moreover, we found that cumulated monthly NEE increased significantly with the average stocking rate. In addition, a confinement experiment was carried out in order to analyze livestock contribution to Total Ecosystem Respiration. Each experiment extended over two days: the first day, cattle was confined in the footprint of the eddy covariance set-up (1.76 ha, 27 LU ha-1) and the second day, it was removed from it. We compared filtered half-hourly data made at 24h intervals, in the presence or absence of cattle, considering that environmental conditions were equivalent (air temperature, wind speed, radiation and wind direction). Results showed that CO2 fluxes were significantly higher when cattle were on the plot. Livestock contribution estimation to CO2 fluxes was on average 6.6 µmol m-2 s-1. [less ▲]

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See detailTemporal variability of nitrous oxide fluxes from a fertilized grassland in Belgium: preliminary results from dynamic closed chambers.
Beekkerk van Ruth, Jöran ULg; Moureaux, Christine ULg; Degré, Aurore ULg et al

Poster (2013, April 09)

Presentation of preliminary results from N2O measurements over a grassland using dynamic closed chambers. See attached folders for more detail.

Detailed reference viewed: 15 (4 ULg)