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See detailBeech phenology and productivity at the Vielsalm Terrestrial Observatory
Hurdebise, Quentin ULiege; Vincke, Caroline; De Ligne, Anne ULiege et al

Poster (2017, October 20)

Temperate forests, as other ecosystems and oceans, mitigate the accumulation in the atmosphere of CO2, the main responsible for the current climate change. It is, therefore, a necessity to understand how ... [more ▼]

Temperate forests, as other ecosystems and oceans, mitigate the accumulation in the atmosphere of CO2, the main responsible for the current climate change. It is, therefore, a necessity to understand how these forests react and will react in a changing environment. That requires long-term simultaneous monitoring of the forest productivity and phenology as well as of climatic variables. Using the 20 years dataset from the Vielsalm Terrestrial Observatory (VTO), an eddy covariance site located in a mixed forest in east Belgium and dominated by beeches, the relations between phenological and productivity indicators were analyzed. Phenological indicators (leaf out beginning, duration and ending as well as leaf fall date) were derived from the relative light transmissivity through the canopy and from the temporal dynamic of the Net Ecosystem Productivity (NEP). No trend was observed for these indicators during the last two decades, but significant relations were found between them and between them and climatic variables. Productivity indicators were derived from eddy covariance measurements (NEP), tree ring widths (growth index) and masting intensity. Growth index was significantly related to the NEP and a reverse proportionality to the masting intensity was found. The analysis of the relation between the beech stand NEP and the phenology gives us evidences that annual NEP is significantly related to the length of the carbon uptake period. A model combining the length of the carbon uptake period and the photosynthetic capacity of the ecosystem was able to predict more than two third of the interannual variability at the VTO. This work underlines the multiplicity of the relation between phenological and productivity indicators. [less ▲]

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See detailLe Grand Chemin du Luxembourg
Hurdebise, Quentin ULiege

Conference given outside the academic context (2017)

Dans le cadre des activités de l'Année Patrimoniale , le dimanche 8 octobre de 16h à 17h30 à l'église Saint-Jacques (Fossse), Quentin Hurdebise fait redécouvrir l'histoire du Grand Chemin du Luxembourg ... [more ▼]

Dans le cadre des activités de l'Année Patrimoniale , le dimanche 8 octobre de 16h à 17h30 à l'église Saint-Jacques (Fossse), Quentin Hurdebise fait redécouvrir l'histoire du Grand Chemin du Luxembourg connu notamment pour le transport des écorces de chênes qui l'empruntait en direction de Stavelot et de Malmedy. Quentin revient sur l'histoire de ce chemin, le contexte dans lequel il a pu naître, les différents noms qui lui sont attribués, ainsi que les différentes curiosités naturelles et historiques qui le jalonnent (faune et flore, maisons et personnages célèbres, croix et monuments, Observatoire Terrestre de Vielsalm, etc.). [less ▲]

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See detailImpact of canopy aerodynamic distance spatial and temporal variability on long term eddy covariance measurements
Hurdebise, Quentin ULiege; Heinesch, Bernard ULiege; De Ligne, Anne ULiege et al

in Agricultural and Forest Meteorology (2017), 247(2017), 131-138

Understanding if and how the spatial and temporal variability of the surrounding environment affects turbulence is essential for long-term eddy covariance measurements. It requires characterizing the ... [more ▼]

Understanding if and how the spatial and temporal variability of the surrounding environment affects turbulence is essential for long-term eddy covariance measurements. It requires characterizing the surrounding environment. One way to achieve this is to analyse the canopy aerodynamic distance (Δ), which is the difference between measurement height (zm) and displacement height (d). In this work, an original method to estimate the canopy aerodynamic distance at a fine spatial (30° sectors) and temporal (one year) resolution was proposed. It was based on sensible heat cospectra analysis, calibrated on a measurement height change and validated using canopy height inventories. This method was applied to 20 years of eddy covariance measurements from the Vielsalm Terrestrial Observatory (VTO), a site located in a mixed temperate forest. The method allowed Δ spatio-temporal variability due to changes in canopy or measurement height to be detected. Relationships between Δ and turbulence statistics were then analysed: the momentum correlation coefficient (ruw) was found to be dependent on Δ, confirming that the measurements were made in the roughness sublayer of the atmospheric surface layer. In contrast, no such relationship was found sensible heat, CO2 or water vapour correlation coefficients, suggesting that the Δ variability did not affect significantly these fluxes. There were significant differences, however, between azimuthal directions, suggesting that these scalars were affected by forest heterogeneity in a different way. Various hypotheses were put forward to explain the differences and their relevance was evaluated. This study highlighted the need to consider the spatial and temporal variability of the surrounding environment in order to verify the consistency of long-term eddy covariance datasets. [less ▲]

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See detailMomentum, sensible heat and CO2 correlation coefficient: what can we learn from 20 years of eddy covariance measurements
Hurdebise, Quentin ULiege; De Ligne, Anne ULiege; Vincke, Caroline et al

Poster (2017, April 24)

Long-term data series of carbon dioxide and other gas exchanges between terrestrial ecosystems and atmosphere become more and more numerous. Long-term analyses of such exchanges require a good ... [more ▼]

Long-term data series of carbon dioxide and other gas exchanges between terrestrial ecosystems and atmosphere become more and more numerous. Long-term analyses of such exchanges require a good understanding of measurement conditions during the investigated period. Independently of climate drivers, measurements may indeed be influenced by measurement conditions themselves subjected to long-term variability due to vegetation growth or set-up changes. The present research refers to the Vielsalm Terrestrial Observatory (VTO) an ICOS candidate site located in a mixed forest (beech, silver fir, Douglas fir, Norway spruce) in the Belgian Ardenne. Fluxes of momentum, carbon dioxide and sensible heat have been continuously measured there by eddy covariance for more than 20 years. During this period, changes in canopy height and measurement height occurred. The correlation coefficients (for momemtum, sensible heat and CO2) and the normalized standard deviations measured for the past 20 years at the Vielsalm Terrestrial Observatory (VTO) were analysed in order to define how the fluxes, independently of climate conditions, were affected by the surrounding environment evolution, including tree growth, forest thinning and tower height change. A relationship between canopy aerodynamic distance and the momentum correlation coefficient was found which is characteristic of the roughness sublayer, and suggests that momentum transport processes were affected by z-d. In contrast, no relationship was found for sensible heat and CO2 correlation coefficients, suggesting that the z-d variability observed did not affect their turbulent transport. There were strong differences in these coefficients, however, between two wind sectors, characterized by contrasted stands (height differences, homogeneity) and different hypotheses were raised to explain it. This study highlighted the importance of taking the surrounding environment variability into account in order to ensure the spatio-temporal consistency of datasets. [less ▲]

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See detailCanopy aerodynamic distance (z-d) estimation and impact on eddy covariance measurements
Hurdebise, Quentin ULiege; De Ligne, Anne ULiege; Vincke, Caroline et al

in Geophysical Research Abstracts 2017 (2017, April 24)

Understanding if and how the spatial and temporal variability of the surrounding environment affects turbulence is essential for long-term eddy covariance measurements above growing and heterogeneous ... [more ▼]

Understanding if and how the spatial and temporal variability of the surrounding environment affects turbulence is essential for long-term eddy covariance measurements above growing and heterogeneous ecosystems. It requires characterizing the surrounding environment. One way to achieve this is to analyse the canopy aerodynamic distance, which is the difference between measurement height (z) and displacement height (d). In this study, twenty years of eddy covariance measurements from the Vielsalm Terrestrial Observatory, a site located in a mixed temperate forest, were used. Canopy aerodynamic distance (z-d) estimates were obtained using two micrometeorological methods: the first one, which is original so far as we know, was based on analysing sensible heat cospectra; the second one was derived from the wind speed profile equation. Canopy height estimates based on inventories were used to validate both methods. The micrometeorological methods allowed the z-d variations due to changes in canopy or measurement height to be detected. In addition, the results obtained using the two methods were well correlated, spatially and temporally, with the z-d derived from canopy height measurements. The micrometeorological approaches used could therefore be a promising tool for investigating z-d variability at a high directional and temporal resolution. Questions remain, however, particularly with regard to the variability observed that cannot be explained by canopy or measurement height variation. Forest management practices and the non-fulfilment of similarity relationships were suspected to be the main explanatory factors. [less ▲]

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See detailVingt ans de mesures des échanges de CO2 et de vapeur d'eau à l'Observatoire Terrestre de Vielsalm
Aubinet, Marc ULiege; Vincke, Caroline; Heinesch, Bernard ULiege et al

Article for general public (2016)

La séquestration du carbone via l'assimilation nette de CO2 par les écosystèmes terrestres varie fortement d'une année à l'autre. La compréhension plus fine de ce phénomène est nécessaire pour pouvoir ... [more ▼]

La séquestration du carbone via l'assimilation nette de CO2 par les écosystèmes terrestres varie fortement d'une année à l'autre. La compréhension plus fine de ce phénomène est nécessaire pour pouvoir prédire si les écosystèmes continueront à se comporter comme des puits de carbone ou si la séquestration va diminuer voire s'inverser complètement, transformant les écosystèmes en source de carbone. Pour mesurer les échanges nets de CO2, des chercheurs ont installé un "Observatoire Terrestre" dans une forêt à Vielsalm qui a permis de mettre en évidence les dynamiques journalière, saisonnière et interannuelle de la séquestration en carbone. La mesure simultanée de l'évapotranspiration réelle permet de plus d'évaluer la consommation en eau des espèces présentes. Les mesures effectuées durant 20 ans montrent que la forêt se comporte comme un puits de carbone. [less ▲]

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See detailOzone concentration and CO2 flux monitoring in a belgian forest
Hurdebise, Quentin ULiege; Bergmans, Benjamin; Aubinet, Marc ULiege

Poster (2016, May 11)

Temperate forests, as other ecosystems and oceans, mitigate the accumulation in the atmosphere of CO2, the main responsible for the current climate change. It is, therefore, a necessity to understand how ... [more ▼]

Temperate forests, as other ecosystems and oceans, mitigate the accumulation in the atmosphere of CO2, the main responsible for the current climate change. It is, therefore, a necessity to understand how these forests react and will react in a changing environment. That requires long-term monitoring of the environment. Tropospheric ozone is one parameter to monitor as it affects the forest by inducing oxidative stress once inside the leaves. Using 16 years of continuous data from an air quality monitoring station managed by the ISSeP (Institut Scientifique de Service Public) located in a mixed forest in east Belgium, we identified ozone concentration extreme events and we investigated their occurrence frequency as well as their relation with climatic variables and air components. As variables are subjected to daily, yearly and inter-annual dynamics, anomalies were used to detect extreme events. To obtain anomalies, we removed the previously mentioned dynamics from half-hourly raw data. Daily and yearly dynamics were removed first and explained 40% of the variability observed in half-hourly ozone concentrations. Then, the inter-annual dynamic was obtained by computing the yearly mean of the residuals, it accounted for 2% of the variability observed. A significant (p<0.01) decreasing trend was observed for these residuals. Determining if that trend is site specific or regionally observed can be done by applying the same analysis to the other sites from the network managed by the ISSeP. No significant trend in the yearly frequency and intensity of extreme events was observed. We used a stepwise regression to identify the variables that explain these extreme events. Significant relations were found between ozone concentration and climatic variables (vapor pressure deficit, temperature, radiation and wind direction) as well as other air components concentration (NO2, NO, NOX, CO). The next step will be to estimate the forest capacity to uptake ozone in order to predict ozone-induced damage and compared it to the CO2 uptake and H2O emissions measured in an ICOS site, the Vielsalm Terrestrial Observatory, located in the same forest at less than 300 meters from the air quality monitoring station. [less ▲]

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

Poster (2016, April 18)

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

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

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See detailThe ICOS Vielsalm Terrestrial Observatory: long term greehouse gas flux measurements
Hurdebise, Quentin ULiege; De Ligne, Anne ULiege

Poster (2015, December 10)

Presentation of the Vielsalm ICOS Terrestrial Observatory: site management, data available, data access, flux temporal dynamic and flux relation with climate variables.

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

Poster (2015, November 18)

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

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

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

Poster (2015, June 04)

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

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

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See detailDetermination of Zinc, Cadmium and Lead Bioavailability in Contaminated Soils at the Single-Cell Level by a Combination of Whole-Cell Biosensors and Flow Cytometry
Hurdebise, Quentin ULiege; Tarayre, Cédric ULiege; Fischer, Christophe ULiege et al

in Sensors (2015)

Zinc, lead and cadmium are metallic trace elements (MTEs) that are widespread in the environment and tend to accumulate in soils because of their low mobility and non-degradability. The purpose of this ... [more ▼]

Zinc, lead and cadmium are metallic trace elements (MTEs) that are widespread in the environment and tend to accumulate in soils because of their low mobility and non-degradability. The purpose of this work is to evaluate the applicability of biosensors as tools able to provide data about the bioavailability of such MTEs in contaminated soils. Here, we tested the genetically-engineered strain Escherichia coli pPZntAgfp as a biosensor applicable to the detection of zinc, lead and cadmium by the biosynthesis of green fluorescent protein (GFP) accumulating inside the cells. Flow cytometry was used to investigate the fluorescence induced by the MTEs. A curvilinear response to zinc between 0 and 25 mg/L and another curvilinear response to cadmium between 0 and 1.5 mg/L were highlighted in liquid media, while lead did not produce exploitable results. The response relating to a Zn2+/Cd2+ ratio of 10 was further investigated. In these conditions, E. coli pPZntAgfp responded to cadmium only. Several contaminated soils with a Zn2+/Cd2+ ratio of 10 were analyzed with the biosensor, and the metallic concentrations were also measured by atomic absorption spectroscopy. Our results showed that E. coli pPZntAgfp could be used as a monitoring tool for contaminated soils being processed. [less ▲]

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See detailSeasonal and inter-annual variability of photosynthetic capacity in a temperate forest
Hurdebise, Quentin ULiege; Vincke, Caroline; Soubie, Rémy et al

Poster (2014, September 23)

In temperate forests, the relation between vegetation phenology and carbon sequestration variability remains to be explored. To study phenology impact on CO2 fluxes, two photosynthetic capacity indicators ... [more ▼]

In temperate forests, the relation between vegetation phenology and carbon sequestration variability remains to be explored. To study phenology impact on CO2 fluxes, two photosynthetic capacity indicators were used : NEE at light saturation (NEEsat) and green proportion in canopy pictures (gcc). Correlations between these indicators were investigated at seasonal and inter-annual scale. [less ▲]

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See detailBioRefine Project: Detection of bioavailability of Metallic Trace Elements in soils by the use of microbial biosensors
Tarayre, Cédric ULiege; Hurdebise, Quentin ULiege; Fischer, Christophe ULiege et al

Poster (2014, September 09)

Zinc, lead and cadmium are the main Metallic Trace Elements (MTEs) found in soils contaminated by the mining industry in Europe. MTEs are spread in the environment because of the disruption of ... [more ▼]

Zinc, lead and cadmium are the main Metallic Trace Elements (MTEs) found in soils contaminated by the mining industry in Europe. MTEs are spread in the environment because of the disruption of biogeochemical cycles caused by human activities. Due to their low mobility and biodegradability, they accumulate in soils where they are strongly bound to particles. It has become necessary to understand interactions between MTEs and the environment and to implement remediation actions. This work is focused on remediation monitoring techniques by using whole cell microbial biosensors able to detect zinc, lead and cadmium. Biosensors provide a signal in response to the bio-available concentration in MTEs, which are valuable for the design of efficient techniques involving bioremediation. Whole cell biosensors used in this work are based on Escherichia coli strains carrying a fluorescent reporter system. The reporter element contains a promoter sensitive to MTEs and a gene coding for the Green Fluorescent Protein (GFP). MTEs activate the synthesis of GFP, which is a very stable protein, causing the accumulation of GFP inside the cells. Then, fluorescence can be measured by flow cytometry. In this study, two biosensors were investigated: E. coli pPzraPgfp and E. coli pPzntAgfp. The last strain provided a linear response to zinc up to 20 mg/l and a curvilinear response to cadmium up to 0.15 mg/l. No detection was highlighted regarding lead. In practical cases, soils and wastes are contaminated by several types of MTEs. Consequently, combined contaminations were also tested. This work allowed highlighting that the strain E. coli pPzntAgfp can be used to assess the bioavailability of cadmium in soils, although the experimental procedure must be improved. This work is supported by the BioRefine Project, a European project in which various member states focus on recovery of inorganics from organic wastestreams. We gratefully acknowledge the INTERREG IVB NWE programme, which financed the BioRefine Project (ref. 320J-BIOREFINE). [less ▲]

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