References of "Heinesch, Bernard"
     in
Bookmark and Share    
Full Text
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 ▲]

Detailed reference viewed: 16 (4 ULg)
See detailYear Round survey of Ocean-Sea Ice-Air Exchanges – the YROSIAE survey
Delille, Bruno ULg; Haskell, T.; Champenois, Willy ULg et al

Conference (2014, March)

YROSIAE survey aimed to carry out a year-round 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 ... [more ▼]

YROSIAE survey aimed to carry out a year-round 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. Ice cores, sea water, brines and exported material were collected at regular intervals about 1 km off cape Evans from November 2011 to December 2011 and from September 2012 to December 2012 in trace-metal clean conditions. Samples are processed to characterize both the vertical distribution and temporal changes of climate gases (CO2, DMS, CH4, N2O), CO2-related parameters (dissolved inorganic carbon, total alkalinity and CaCO3 amount), physical parameters (salinity, temperature, texture, 18O), biogeochemical parameters (macro-nutrients, particulate and dissolved organic carbon, δ13C, δ30Si and δ15N, micro-nutrients - including iron) and biological parameters ( chlorophyll a, primary production within sea ice derived from O2:Ar and O2:N ratios, autotrophic species determination, bacterial cell counts a.s.o.). In addition, we deployed a micro-meterological tower and automatic chambers to measure air-ice CO2 fluxes. Continuous measurements of ice temperature and ice accretion or melting, both at the ice-ocean and the ice-atmosphere interfaces were provided by an “Ice-T” ice mass balance buoy. Sediment traps collected particles below the ice between 10 and 70 m, while dust collectors provided a record of a full suite of trace metal and dust at different levels above the ground. We will present the aims, overall approach and sampling strategy of the YROSIAE survey. In addition we will also discuss CO2 dynamics within the ice and present temporal air-ice CO2 fluxes over the year. We will provide a first budget of air-ice CO2 fluxes during ice growth for Antarctica sea ice and discuss the impact of the snow cover on air-ice CO2 fluxes. [less ▲]

Detailed reference viewed: 36 (5 ULg)
Full Text
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 ▲]

Detailed reference viewed: 43 (12 ULg)
Full Text
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 ▲]

Detailed reference viewed: 5 (0 ULg)
Full Text
Peer Reviewed
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

Detailed reference viewed: 35 (9 ULg)
Full Text
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 ▲]

Detailed reference viewed: 45 (13 ULg)
Full Text
Peer Reviewed
See detailPhotosynthesis-dependent isoprene emission from leaf to planet in a global carbon-chemistry-climate model
Unger, N.; Harper, K.; Zheng, Y. et al

in Atmospheric Chemistry and Physics (2013), 13

We describe the implementation of a biochemical model of isoprene emission that depends on the electron requirement for isoprene synthesis into the Farquhar–Ball–Berry leaf model of photosynthesis and ... [more ▼]

We describe the implementation of a biochemical model of isoprene emission that depends on the electron requirement for isoprene synthesis into the Farquhar–Ball–Berry leaf model of photosynthesis and stomatal conductance that is embedded within a global chemistry-climate simulation framework. The isoprene production is calculated as a function of electron transport-limited photosynthesis, intercellular and atmospheric carbon dioxide concentration, and canopy temperature. The vegetation biophysics module computes the photosynthetic uptake of carbon dioxide coupled with the transpiration of water vapor and the isoprene emission rate at the 30 min physical integration time step of the global chemistry-climate model. In the model, the rate of carbon assimilation provides the dominant control on isoprene emission variability over canopy temperature. A control simulation representative of the present-day climatic state that uses 8 plant functional types (PFTs), prescribed phenology and generic PFT-specific isoprene emission potentials (fraction of electrons available for isoprene synthesis) reproduces 50% of the variability across different ecosystems and seasons in a global database of 28 measured campaign-average fluxes. Compared to time-varying isoprene flux measurements at 9 select sites, the model authentically captures the observed variability in the 30 min average diurnal cycle (R2 = 64–96 %) and simulates the flux magnitude to within a factor of 2. The control run yields a global isoprene source strength of 451 TgC yr−1 that increases by 30% in the artificial absence of plant water stress and by 55% for potential natural vegetation. [less ▲]

Detailed reference viewed: 43 (10 ULg)
Full Text
Peer Reviewed
See detailÉlaboration du référentiel de compétences du master bioingénieur en Sciences et Technologies de l'Environnement
Colaux-Castillo-Bocanegra, Catherine ULg; Colinet, Gilles ULg; Debouche, Charles ULg et al

in Poulin, Richard (Ed.) Séminaire CITEF 2013 La liaison formation-emploi : l'approche compétences et la formation tout au long de la vie (2013, October 18)

Le département des Sciences et Technologies de l’Environnement (STE) de Gembloux Agro-Bio Tech faculté de l’Université de Liège a profité d’un changement d’intitulé de son diplôme de bioingénieur pour ... [more ▼]

Le département des Sciences et Technologies de l’Environnement (STE) de Gembloux Agro-Bio Tech faculté de l’Université de Liège a profité d’un changement d’intitulé de son diplôme de bioingénieur pour réviser son programme des études. Pour ce faire, il a adopté l’approche compétence. Afin de préparer au mieux ses futurs diplômés aux attentes du monde professionnel actuel et à venir, des anciens diplômés et des employeurs potentiels ont participé à la validation du référentiel de compétences associé à cette formation. Cette publication reprend les étapes clés de la création du référentiel de compétences et son exploitation dans la conception d’un programme des études cohérent. [less ▲]

Detailed reference viewed: 63 (18 ULg)
Full Text
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 ▲]

Detailed reference viewed: 78 (16 ULg)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 14 (0 ULg)
Full Text
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 ▲]

Detailed reference viewed: 83 (15 ULg)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 14 (2 ULg)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 20 (5 ULg)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 131 (17 ULg)
See detailMéthodologie de calcul des flux turbulents : Corrections de fréquence
Heinesch, Bernard ULg

Conference (2013, January 29)

Detailed reference viewed: 13 (1 ULg)
See detailMéthodologie de calcul des flux turbulents : rotation du système de coordonnées
Heinesch, Bernard ULg

Conference (2013, January 28)

Detailed reference viewed: 13 (1 ULg)
Full Text
Peer Reviewed
See detailPhysical and biogeochemical properties in landfast sea ice (Barrow, Alaska): insights on brine and gas dynamics across seasons
Zhou, Jiayun ULg; Delille, Bruno ULg; Eicken, H. et al

in Journal of Geophysical Research (2013), 118(6), 3172-3189

The impacts of the seasonal evolution of sea-ice physical properties on ice-ocean biogeochemical exchanges were investigated in landfast ice at Barrow (Alaska) from January through June 2009. Three stages ... [more ▼]

The impacts of the seasonal evolution of sea-ice physical properties on ice-ocean biogeochemical exchanges were investigated in landfast ice at Barrow (Alaska) from January through June 2009. Three stages of brine dynamics across the annual cycle have been identified based on brine salinity, brine volume fraction and porous medium Rayleigh number [less ▲]

Detailed reference viewed: 30 (9 ULg)
Full Text
See detailCurrent net ecosystem exchange of CO2 in a young mixed forest: any heritage from the previous ecosystem?
Violette, Aurélie ULg; Heinesch, Bernard ULg; Erpicum, Michel ULg et al

Poster (2013)

For 15 years, networks of flux towers have been developed to determine accurate carbon balance with the eddy-covariance method and determine if forests are sink or source of carbon. However, for ... [more ▼]

For 15 years, networks of flux towers have been developed to determine accurate carbon balance with the eddy-covariance method and determine if forests are sink or source of carbon. However, for prediction of the evolution of carbon cycle and climate, major uncertainties remain on the ecosystem respiration (Reco, which includes the respiration of above ground part of trees, roots respiration and mineralization of the soil organic matter), the gross primary productivity (GPP) and their difference, the net ecosystem exchange (NEE) of forests. These uncertainties are consequences of spatial and inter-annual variability, driven by previous and current climatic conditions, as well as by the particular history of the site (management, diseases, etc.). In this study we focus on the carbon cycle in two mixed forests in the Belgian Ardennes. The first site, Vielsalm, is a mature stand mostly composed of beeches (Fagus sylvatica) and douglas fir (Pseudotsuga menziesii) from 80 to 100 years old. The second site, La Robinette, was covered before 1995 with spruces. After an important windfall and a clear cutting, the site was replanted, between 1995 and 2000, with spruces (Piceas abies) and deciduous species (mostly Betula pendula, Aulnus glutinosa and Salix aurita). The challenge here is to highlight how initial conditions can influence the current behavior of the carbon cycle in a growing stand compared to a mature one, where initial conditions are supposed to be forgotten. A modeling approach suits particularly well for sensitivity tests and estimation of the temporal lag between an event and the ecosystem response. We use the forest ecosystem model ASPECTS (Rasse et al., Ecological Modelling 141, 35-52, 2001). This model predicts long-term forest growth by calculating, over time, hourly NEE. It was developed and already validated on the Vielsalm forest. Modelling results are confronted to eddy-covariance data on both sites from 2006 to 2011. The main difference between both sites seems to rely on soil respiration, which is probably partly a heritage of the previous ecosystem at the young forest site. [less ▲]

Detailed reference viewed: 22 (10 ULg)