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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 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 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 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 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 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.

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See detailTEMPORAL VARIABILITY OF N2O FLUXES FROM A FERTILIZED GRASSLAND: PRELIMINARY RESULTS FROM DYNAMIC CLOSED CHAMBERS
Beekkerk van Ruth, Jöran ULg; Moureaux, Christine ULg; Degré, Aurore ULg et al

Poster (2013, April 09)

This work presents preliminary results of nitrous oxide (N2O) fluxes measured by dynamic closed chambers from a fertilized grassland grazed by the Belgian Blue breed of cattle. It is part of a project ... [more ▼]

This work presents preliminary results of nitrous oxide (N2O) fluxes measured by dynamic closed chambers from a fertilized grassland grazed by the Belgian Blue breed of cattle. It is part of a project funded by the public service of Wallonia (SPW-DGARNE), whose objectives are to make a carbon/CO2 balance of the grassland (Jérôme et al., 2013) and to quantify CH4 (Dumortier et al., 2013) and N2O fluxes. The site is located in Dorinne (Dorinne Terrestrial Observatory), Belgium (50° 18’ 44” N; 4° 58’ 07” E; 248 m al.). It is a permanent grassland of ca. 4.2 ha with a moderate slope of 1 to 2 %. Mineral fertilisation took place in March and May 2012. Two cylindrical chambers of 19,2 cm diameter and 11,5 cm height were placed inside a protected area around a micrometeorological station. An infrared gas analyser (Thermofischer 46i) was used in order to measure the N2O concentrations inside of the chambers, closed by automatically controlled lids and ventilated by a constant air flow of 1liter/min. These devices were completed by adjacent soil humidity and temperature sensors. The first measurement campaign took place during June and July 2012. The chambers were installed in the field and N2O fluxes were followed without manipulation. N2O fluxes were characterised by a background emission (between 2 and 10 ngN.m2s􀀀1) on which intense but time limited peaks (between 50 and 300 ngN.m2s􀀀1) superimposed. Peaks were found to be mainly linked to fertilisation and driven by precipitation. Background fluxes were found to correlate positively with soil temperature. Secondly, a manipulation experiment took place in November 2012: two different fertilizer treatments were applied to the chambers. Doses of respectively 100 and 200 kg N/ha of ammonium nitrate were sprayed in the chambers (equivalent to a 8mmprecipitation). N2O fluxes peaked shortly after fertiliser application (respectively 300 and 550 ngN.m2s􀀀1), as well as after a posterior rain event (respectively 800 and 1500 ngN.m2s􀀀1). The peak dynamics suggests a complex interaction between soil humidity and nitrogen availability, which is under study. Dumortier et al., Geophysical Research Abstracts, Vol. 15, EGU2013-2083-1, 2013 Jérôme et al., Geophysical Research Abstracts Vol. 15, EGU2013-6989, 2013 [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 detail10. Environnement et gaz à effet de serre
Moureaux, Christine ULg; Aubinet, Marc ULg; Bodson, Bernard ULg

in Bodson, Bernard; Destain, Jean-Pierre (Eds.) Livre Blanc - Céréales (2013, February 27)

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

in Communications in Agricultural and Applied Biological Sciences (2013, February), 78(1), 127-132

VOC (volatile organic compounds) include a wide set of molecules which are mostly emitted by the plants. Atmospheric scientists are strongly interested in these compounds because of their important role ... [more ▼]

VOC (volatile organic compounds) include a wide set of molecules which are mostly emitted by the plants. Atmospheric scientists are strongly interested in these compounds because of their important role in the atmospheric chemistry and their final impact on air pollution and climate change. Evaluation of current and future VOC emissions is thus necessary and requires a comprehensive understanding of VOC production and exchange dynamics under a wide panel of climatic conditions and ecosystems. Forest and non pastured grasslands have been largely studied for the last decade. However, knowledge about VOC fluxes from croplands remains scarce. Our study focuses on the VOC exchanges between a maize field and the atmosphere. It is incorporated in a wider project that aims to study VOC fluxes from two croplands (maize and winter wheat) and a pastured grassland. VOC fluxes have been measured on a maize field during the whole growing season using a micrometeorological method (eddy covariance). While first results show half-hourly bidirectionnal exchanges among all the preselected compounds, in average methanol stands for the greatest emitted VOC, followed by green leaf volatiles, and acetic acid is the greatest taken up VOC. Small isoprene and monoterpenes 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. These environmental controls will be further investigated [less ▲]

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See detailAntarctic urchin ctenocidaris speciosa spines: Lessons from the deep
Catarino, A. I.; av FD Roosevelt 50, Brussels; Guibourt, V. et al

in Cahiers de Biologie Marine (2013), 54(4), 649-655

Ocean acidification is leading to changes in the oceanic carbonate system. As a result, calcium carbonate saturation horizon is shallowing, especially at high latitudes. Biogenic high magnesium-calcites ... [more ▼]

Ocean acidification is leading to changes in the oceanic carbonate system. As a result, calcium carbonate saturation horizon is shallowing, especially at high latitudes. Biogenic high magnesium-calcites could be particularly vulnerable, since their solubility is either similar or greater than that of aragonite. Cidaroid urchins have magnesium-calcite spines covered by a polycrystalline cortex which becomes exposed to seawater when mature (not covered by an epidermis). However, deep species live at low calcium carbonate saturation states, especially at high latitudes. We describe here the morphology and the magnesium content of Ctenocidaris speciosa spines collected at different depths from the Weddell Sea (Antarctica) and relate the features with seawater calcium carbonate saturation. We observed that the spines cortex of C. speciosa presented a thicker inner cortex layer and a lower [Mg2] below the aragonite saturation horizon. We suggest that the cortex of cidaroid spines is able to resist to low calcium carbonate saturation state. [less ▲]

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See detailStockage de carbone et flux de gaz à effet de serre en prairie (synthèse bibliographique)
Jerome, Elisabeth ULg; Beckers, Yves ULg; Bodson, Bernard ULg et al

in Biotechnologie, Agronomie, Société et Environnement = Biotechnology, Agronomy, Society and Environment [=BASE] (2013), 17(1), 103-117

Grassland carbon (C) sequestration can play an important role in mitigating total greenhouse gas (GHG) emissions of livestock production systems. An accurate inventory of livestock production system ... [more ▼]

Grassland carbon (C) sequestration can play an important role in mitigating total greenhouse gas (GHG) emissions of livestock production systems. An accurate inventory of livestock production system contribution to GHG emissions requires to think in terms of global budget, by considering both the GHG sources and the mitigation potential trough grassland soil carbon sequestration. There is a huge variability in C and GHG balances of grasslands that is mainly due to management practices and climatic conditions. The present article shows that, to reduce the uncertainties of the results, long term measurements at the field scale are necessary. Also, it shows the importance of taking the fluxes of the three main GHGs (carbon dioxide, nitrous oxide, methane) into account when calculating the GHG budget. This article also highlights the need for a better understanding of the mechanisms driving the fluxes, in relation to environmental factors and management practices, in order to propose mitigation strategies able to enhance soil carbon sequestration in soils and to reduce methane and nitrous oxide emissions. [less ▲]

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See detailEvaluation of the potential of MODIS satellite data to predict vegetation phenology in different biomes: An investigation using ground-based NDVI measurements
Hmimina, G.; Dufrêne, Eric; Pontailler, J.-Y. et al

in Remote Sensing of Environment (2013), (132), 145-158

Vegetation phenology is the st udy of the timing of seasonal events that are considered to be the result of adaptive responses to climate variations on short and long time scales. In the field of remote ... [more ▼]

Vegetation phenology is the st udy of the timing of seasonal events that are considered to be the result of adaptive responses to climate variations on short and long time scales. In the field of remote sensing of vegetation phenology, phenologicalmetrics are derived fromtime series of optical data. For that purpose, considerable effort has been specifically focused on developing noise reduction and cloud-contaminated data removal techniques to improve the quality of remotely-sensed time series. Comparative studies between time series composed of satellite data acquired under clear and cloudy conditions and fromradiometric data obtainedwith high accuracy fromground-basedmeasurements constitute a direct and effective way to assess the operational use and limitations of remote sensing for predicting the main plant phenological events. In the present paper, we sought to explicitly evaluate the potential use of MODerate resolution Imaging Spectroradiometer (MODIS) remote sensing data for monitoring the seasonal dynamics of different types of vegetation cover that are representative of the major terrestrial biomes, including temperate deciduous forests, evergreen forests, African savannah, and crops. After cloud screening and filtering, we compared the temporal patterns and phenological metrics derived from in situ NDVI time series and from MODIS daily and 16-composite products. We also evaluated the effects of residual noise and the in uence of data gaps in MODIS NDVI time series on the identification of the most relevant metrics for vegetation phenology monitoring. The results show that the in exion points of a model fitted to a MODIS NDVI time series allow accurate estimates of the onset of greenness in the spring and the onset of yellowing in the autumn in deciduous forests (RMSE<oneweek). Phenologicalmetrics identical to those providedwith theMODIS Global Vegetation Phenology product (MDC12Q2) are less robust to data gaps, and they can be subject to large biases of approximately twoweeks or more during the autumn phenological transitions. In the evergreen forests, in situ NDVI time series describe the phenology with high fidelity despite small temporal changes in the canopy foliage. However, MODIS is unable to provide consistent phenological patterns. In crops and savannah, MODIS NDVI time series reproduce the general temporal patterns of phenology, but significant discrepancies appear between MODIS and ground-based NDVI time series during very localized periods of time depending on the weather conditions and spatial heterogeneity within the MODIS pixel. In the rainforest, the temporal pattern exhibited by a MODIS 16-day composite NDVI time series ismore likely due to a pattern of noise in the NDVI data structure according to both rainy and dry seasons rather than to phenological changes. More investigations are needed, but in all cases, this result leads us to conclude that MODIS time series in tropical rainforests should be interpreted with great caution. [less ▲]

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See detailCarbon balance of an intensive grazed grassland
Jerome, Elisabeth ULg; Beckers, Yves ULg; Bodson, Bernard ULg et al

Poster (2012, April 23)

This work seeks to analyze the C balance of a Belgian grassland grazed by the “Blanc Bleu Belge” breed of cattle. The site is located at Dorinne in the Belgian Condroz (50° 18’ 44’’ N; 4° 58’ 07’’ E; 248 ... [more ▼]

This work seeks to analyze the C balance of a Belgian grassland grazed by the “Blanc Bleu Belge” breed of cattle. The site is located at Dorinne in the Belgian Condroz (50° 18’ 44’’ N; 4° 58’ 07’’ E; 248 m asl.). It is permanent grassland of ca. 4.2 ha with a moderate slope of 1 to 2 %. Homogeneity and topography criteria are met to ensure high quality turbulent flux measurements. The experimental field was equipped with an eddy covariance system. Flux correction, quality control and data gap filling were performed following standardised procedures. This device was completed by a micrometeorological station that measured temperature and humidity respectively in the air and within the soil, radiation, atmospheric pressure and precipitations. Carbon exported through mowing (CNBP,export), imported through compost application (CNBP,import) or through complementary feeds for cattle (CNBP,complement) was also measured. In addition, the vegetation development was followed in order to estimate herbage production and dry matter intake by grazing animals. Carbon lost through CH4 emissions (CNBP,CH4) was finally estimated, allowing the establishment of a full C budget. After one year of measurements (May 2010 - May 2011), the grassland was a net CO2 source (Net Ecosystem Exchange (NEE) = 172 ± 94 g C m-2 year-1). Net Biome Productivity (NBP) was calculated from NEE by taking into account imports and export of organic C and losses of carbon as CH4. Contribution of CNBP,CH4 to NBP was small as it was 12 ± 1 g C m-2 year-1. The balance between CNBP,import and CNBP,export created not such a large departure of NBP from NEE, which is not the case of CNBP,complement. The NBP was finally estimated at 102 ± 95 g C m-2 year-1. At this stage, it is premature to conclude about the sink or source behaviour of the plot because the NBP value is very close to its uncertainty. Moreover, this result was obtained under particular climate conditions, characterised by drought during summer 2010 and spring 2011. First year full carbon budget will be discussed in relation with climate conditions and management practices. A second year of measurements will be also presented. [less ▲]

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See detailCarbon balance of a grazed grassland in Belgium
Jerome, Elisabeth ULg; Beckers, Yves ULg; Bodson, Bernard ULg et al

in Communications in Agricultural and Applied Biological Sciences (2012, February 10)

This work seeks to analyze the carbon balance of a managed permanent grassland grazed by the “Blanc Bleu Belge” breed of cattle. The study site is located at Dorinne. The experimental field was equipped ... [more ▼]

This work seeks to analyze the carbon balance of a managed permanent grassland grazed by the “Blanc Bleu Belge” breed of cattle. The study site is located at Dorinne. The experimental field was equipped with an eddy covariance system that measured CO2 fluxes and with a micrometeorological station. Carbon exported through mowing, imported through compost application or through complementary feeds for cattle was also measured. Carbon lost through CH4 emissions was finally estimated, allowing the establishment of a full C budget. In addition, the vegetation development was followed in order to estimate herbage production and dry matter intake by grazing animals. First year full carbon budget is presented and discussed, in relation with climate conditions and management practices. [less ▲]

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