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See detailThe use of the Vadose Zone Experimental Setup as an innovative in situ characterization method for the vadose zone: a case study at an industrial contaminated site in Belgium
Fernandez de Vera, Natalia ULg; Beaujean, Jean ULg; Jamin, Pierre ULg et al

Conference (2015, September)

The development of protection and remediation plans for contaminated soil and groundwater require a detailed understanding of the transport of pollutants in the subsurface. However, such understanding is ... [more ▼]

The development of protection and remediation plans for contaminated soil and groundwater require a detailed understanding of the transport of pollutants in the subsurface. However, such understanding is affected by the lack of spatial and temporal coverage provided by the current in situ characterization technologies. A new system has been developed in order to overcome such limitations. The vadose zone experimental setup is a new development combining cross-hole geophysics and the Vadose Zone Monitoring System (VMS). In cross-hole geophysics, an injection of an electrical current using electrodes installed in vertical boreholes is triggered. From measured potential differences, spatial patterns related with subsurface heterogeneities, water content and solute concentrations are inferred. The VMS allows continuous measurements of water content at different depths of the vadose zone, as well as water sampling. The system is formed by a flexible sleeve containing monitoring units along its depth which is installed in a slanted borehole. The system was installed at a former industrial site in Belgium, where soil and groundwater are contaminated with BTEX, PAH, and heavy metals. Two VMS were installed in two slanted boreholes on site, together with four vertical boreholes containing electrodes for geophysical measurements. The site was initially monitored under natural recharge conditions. Water content sensors located along the VMS registered fast wetting and draining reactions to rainfall events followed by the activation of water transport through fractures. Results from soil water samples show continuous evolution of water chemistry with depth, due to disequilibrium between infiltrated water and the hydrochemical conditions in the unsaturated zone. Subsequently, a saline tracer was injected in the surface. The transport of the tracer in the subsurface was monitored via cross-hole and surface geophysics. Results from imaging reflect the evolution of a plume through vertical and lateral transport and dilution. [less ▲]

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See detailVADOSE ZONE STUDIES AT AN INDUSTRIAL CONTAMINATED SITE: THE VADOSE ZONE MONITORING SYSTEM AND CROSS-HOLE GEOPHYSICS
Fernandez de Vera, Natalia ULg; Beaujean, Jean ULg; Jamin, Pierre ULg et al

Conference (2014, September 03)

In situ vadose zone characterization is essential to improve risk characterization and remediation measures for soil and groundwater contamination. However, most available technologies have been developed ... [more ▼]

In situ vadose zone characterization is essential to improve risk characterization and remediation measures for soil and groundwater contamination. However, most available technologies have been developed in the context of agricultural soils. Most of these methodologies are not applicable at industrial sites, where soils and contamination differ in origin and composition. In addition, they are applicable only in the first meters of soils, leaving deeper vadose zones with lack of information, in particular on field scale heterogeneity. To overcome such difficulties, a vadose zone experiment has been setup at a former industrial site in Belgium. Industrial activities carried out on site left a legacy of soil and groundwater contamination in BTEX, PAH, cyanide and heavy metals. The experiment involves the combination of two techniques: the Vadose Zone Monitoring System (VMS) and cross-hole geophysics. The VMS allows continuous measurements of water content at different depths of the vadose zone (Dahan et al., 2009). In addition, it provides the possibility of pore water sampling at different depths. The system is formed by a flexible sleeve installed in a slanted borehole (Fig. 1) and containing monitoring units along its depth (Fig. 2). The flexible sleeve contains three types of monitoring units in the vadose zone: Time Domain Transmissometry (TDT), which allows water content measurements; Vadose Sampling Ports (VSP), used for collecting water samples coming from the matrix; and the Fracture Samplers (FS), which are used for retrieving water samples from the fractures. Cross-hole electrical tomography measurements are carried providing detailed spatial patterns about electrical properties of the subsurface. Such properties are related with subsurface heterogeneities, water content and solute concentrations. Two VMS were installed on site, together with four vertical boreholes containing electrodes for geophysical measurements. The site has been monitored under natural recharge conditions during the summer, autumn and winter. Results show reactions in the soil at depths up to 6m as a consequence of rainfall infiltration and groundwater level fluctuations. In addition, the chemistry of the soil water changes with depth and water infiltration. Background images obtained from geophysical measurements show a highly conductive subsurface due to the lithologies and the high mineralization of the water in the vadose zone. The combination of cross-hole geophysics with the VMS has provided an effective tool for characterizing the chemistry and the structure of the vadose zone. [less ▲]

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See detailFactors controlling soil organic carbon persistence along an eroding hillslope on the loess belt
Wiaux, François; Cornelis, Jean-Thomas ULg; Vanclooster, Marnik et al

in Soil Biology & Biochemistry (2014), 77

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See detailThe synergetic effect of moisture protection, substrate quality and biotic acclimation on soil organic carbon persistence along a cultivated loamy hillslope
Wiaux, François; Vanclooster, Marnik; Cornelis, Jean-Thomas ULg et al

Poster (2013)

Abstract : The combination of hydrologic, geomorphic and biogeochemical approaches is required to determine organic carbon (OC) persistence and dynamics within landscapes. Here, we used soil in-situ ... [more ▼]

Abstract : The combination of hydrologic, geomorphic and biogeochemical approaches is required to determine organic carbon (OC) persistence and dynamics within landscapes. Here, we used soil in-situ surface heterotrophic respiration measurement as an indicator of OC persistence along a hillslope (crop field on the loess belt Under temperate climate), characterized by an important erosion-induced OC stock colluvium downslope. Along this topographical gradient, we quantified the space-time structure of soil water and temperature, and soil OC amount and quality (from a chemical point of view based on NaOCl oxidation) in relation to CO2 fluxes. We used a Generalized Least Square (GLS) regression model to identify the role of each abiotic factor as well as their interactions on observed soil respiration rates, and to calculate time-average values of these CO2 fluxes at each studied slope positions. [less ▲]

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See detailDistribution, leaching and flux measurements of contaminants in the vadose zone of industrial contaminated sites: a review
Fernandez de Vera, Natalia ULg; Vanclooster, Marnik; Brouyère, Serge ULg

Report (2012)

This document is a review of state of science regarding flux measurement technologies in the vadose zone. Initially, a description of distribution and leaching of inorganic contaminants in the vadose zone ... [more ▼]

This document is a review of state of science regarding flux measurement technologies in the vadose zone. Initially, a description of distribution and leaching of inorganic contaminants in the vadose zone is provided. Such description is followed by a review of vadose zone techniques that are applied for measuring contaminant fluxes. At the end of the document the applicability of such techniques to industrial contaminated sites is discussed. [less ▲]

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See detailSpace-time dynamics of soil respiration link to the C pool distribution at the hillslope scale
Wiaux, François; Cornelis, Jean-Thomas ULg; Van Oost, Kristof et al

in Geophysical Research Abstracts (2012), 14(EGU2012), 7937

Abstract : A crucial issue in soil C dynamics modelling is to develop models suitable for regional scale, but based on local and short-time scale observations. Recent research has illustrated the strong ... [more ▼]

Abstract : A crucial issue in soil C dynamics modelling is to develop models suitable for regional scale, but based on local and short-time scale observations. Recent research has illustrated the strong linkage between SOC dynamics and landscape processes. There is increasing evidence that lateral fluxes of SOC, sediment and water will further enhance the variability of SOC dynamics, especially on agricultural land. Hence, in this study, we aim to improve our understanding of soil C dynamics by quantifying the soil respiration response of carbon pools at different positions along a slope catena, characterized by different soil moisture and temperature conditions and by different SOC stock and C pool distributions. The study was performed on a hillslope in the belgian loamy belt. Time series of soil moisture, temperature and surface CO2 fluxes were monitored on a regular basis (at least once a week, during spring and autumn 2011) along the hillsope, at the soil surface. At the same positions, soil cores (1 to 1.5 m depth) were collected and analyzed for SOC, C distribution (using a chemical fractionation), mineral oxides (oxalate extractions), pH, and texture. Our results show that substantial lateral transport of soil materials takes place along this hillslope, with a continuous burying of surface C and minerals at the bottom of the slope. This results in the development of a colluvial soil with an increasing SOC stock. This colluvial C stock mainly consists of labile C (66%), and this labile C stock in the colluvium is 3.5 higher than the labile C stock at the other slope positions. This stock is thus poorly stabilized and has a higher potential for mineralization. The other part of this C stock is stabilized by organo-mineral associations (19%) or is recalcitrant C (15%). Compared to the other slope positions, this colluvial stable C stock is significant, as it is 1.5 to 2 times higher. The spatial gradient of the measured soil respiration is consistent with the previous C pool distribution observations along the hillslope, since there is a significant higher respiration at the bottom of the slope (colluvial area) than at the other slope positions. The measured temporal dynamics of the soil respiration is explained by moisture and temperature variations. This measured space-time dynamics, completed with further additional field measurement campaigns, will be the basis for calibrating and validating hillslope scale soil C turn-over models. [less ▲]

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See detailValorisation de la Carte Numérique des Sols de Wallonie et d’une base de données disponible en analyse de sols, dans le cadre de l’évaluation du risque de pollution des eaux souterraines par les pesticides
Bah, Boubacar Billo ULg; Vanclooster, Marnik; Oger, Robert ULg et al

in Biotechnologie, Agronomie, Société et Environnement = Biotechnology, Agronomy, Society and Environment [=BASE] (2011), 15(S2), 709-726

This study shows how the Digital Soil Map of Wallonia and the associated soil database Aardewerk can be combined with the MetaPEARL model to assess the sensitivity of agricultural soils to pesticide ... [more ▼]

This study shows how the Digital Soil Map of Wallonia and the associated soil database Aardewerk can be combined with the MetaPEARL model to assess the sensitivity of agricultural soils to pesticide transfer into underground water tables in Wallonia (Southern Belgium). MetaPEARL is based on an analytical expression which describes the concentration of leached pesticides at the soil profile bottom depending on available data on soil characteristics, climate and pesticide properties. The results show an important soil sensitivity to pesticide transfer with a coefficient of retention on organic matter (Kom) very weak (about 10 dm3.kg-1) or with a relatively high half-life time (DT50 about 60 days). In this case, the pesticide is weakly retained by soil organic matter or slowly degraded and then stays available in the soil and can be quickly leached during rainfalls. In other respects, the pesticide sensitivity to leaching is strongly correlated with soil texture and its organic matter content. It is also observed that the concentration of leached pesticide is strongly depending of the rainfall surplus (water flux into the soil or hydrous balance). A sensitivity analysis has shown that the model is very sensitive to soil thickness, to organic matter content, to the bulk density of the mineral fraction by textural classes and of the organic matter. Therefore, these pedological variables have to be assessed with the highest precision to avoid adding further uncertainty to the predictions obtained. On the basis of the most sensitive soil variables, the analysis of “spatial” uncertainty related to the results delivered by MetaPEARL, due to the consideration of an unique representative value by soil type and by region (deterministic approach), shows that this approach tends to under-estimate the concentration of pesticide leached in the soil. And that compared to the use of a stochastic simulation (probabilistic approach) which takes into account the soil characteristic variability within a given soil type. This stochastic approach allows also the calculation of a more relevant threshold of risk probability (percentile) which can be compared to an imposed standard in view to enhance a sustainable management of natural resources. [less ▲]

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See detailPESTEAUX: Implementing MetaPEARL for the Walloon Region in Belgium
Bah, Boubacar Billo ULg; Vanclooster, Marnik; Oger, Robert ULg

Scientific conference (2011, March 29)

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See detailÉvaluation de la sensibilité des sols au transfert des pesticides vers les eaux souterraines en Wallonie (Belgique) avec le métamodèle MetaPEARL
Bah, Boubacar Billo ULg; Mattern, Samuel; Vanclooster, Marnik et al

in Milieux Poreux et Transferts Hydriques (2010), 56

Cette étude présente l'utilisation du métamodèle MetaPEARL pour évaluer la sensibilité des sols au transfert des pesticides vers les eaux souterraines en Wallonie. MetaPEARL prédit la concentration de ... [more ▼]

Cette étude présente l'utilisation du métamodèle MetaPEARL pour évaluer la sensibilité des sols au transfert des pesticides vers les eaux souterraines en Wallonie. MetaPEARL prédit la concentration de pesticide lixivié au bas du profil pédologique en fonction de données facilement disponibles sur les sols, le climat, et les propriétés des pesticides. MetaPEARL a été appliqué pour quatre pesticides génériques A, B, C et D (FOCUS, 2000). Les résultats obtenus montrent une sensibilité plus importante des sols de Wallonie aux transferts des pesticides de type A et B, permettant ainsi de distinguer des régions relativement contrastées d'un point de vue de la sensibilité de leurs sols au transfert des pesticides vers les eaux souterraines. Ce contraste régional est corrélé d'une part à la variabilité régionale des teneurs en matière organique des sols, et d'autre part au gradient pluviométrique nord-sud observé en Wallonie. On constate également que la concentration en pesticide lixivié est plus importante en automne qu'au printemps. [less ▲]

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See detailEvaluation de la sensibilité des sols au transfert de pesticides vers les eaux souterraines en Région wallonne (Belgique)
Bah, Boubacar Billo ULg; Mattern, Samuel; Vanclooster, Marnik et al

in Actes des 35èmes Journées du Groupe Francophone Humidimétrie et TraNsferts en milieux poreux (GFHN), Louvain-la-Neuve, Belgique, 23-25 novembre 2010 (2010, November)

Cette étude présente l'utilisation du métamodèle MetaPEARL (Tiktak et al., 2006) pour évaluer la sensibilité des sols au transfert des pesticides vers les eaux souterraines en Wallonie. MetaPEARL prédit ... [more ▼]

Cette étude présente l'utilisation du métamodèle MetaPEARL (Tiktak et al., 2006) pour évaluer la sensibilité des sols au transfert des pesticides vers les eaux souterraines en Wallonie. MetaPEARL prédit la concentration de pesticide lixivié au bas du profil pédologique en fonction de données facilement disponibles sur les sols, le climat, et les propriétés des pesticides. MetaPEARL a été appliqué pour quatre pesticides génériques A, B, C et D (FOCUS, 2000). Les résultats obtenus montrent une sensibilité plus importante des sols de Wallonie aux transferts des pesticides de type A et B, permettant ainsi de distinguer des régions relativement contrastées d’un point de vue de la sensibilité de leurs sols au transfert des pesticides vers les eaux souterraines. Ce contraste régional est corrélé d’une part à la variabilité régionale des teneurs en matière organique des sols, et d’autre part au gradient pluviométrique nord-sud observé en Wallonie. On constate également que la concentration en pesticide lixivié est plus importante en automne qu’au printemps. [less ▲]

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See detailSoil surface water content estimation by full-waveform GPR signal inversion in the presence of thin layers
Minet, Julien ULg; Lambot, Sébastien; Slob, Evert C. et al

in IEEE Transactions on Geoscience and Remote Sensing (2010), 48

We analyzed the effect of shallow thin layers on the estimation of soil surface water content using full-waveform inversion of off-ground ground penetrating radar (GPR) data. Strong dielectric contrasts ... [more ▼]

We analyzed the effect of shallow thin layers on the estimation of soil surface water content using full-waveform inversion of off-ground ground penetrating radar (GPR) data. Strong dielectric contrasts are expected to occur under fast wetting or drying weather conditions, thereby leading to constructive and destructive interferences with respect to the surface reflection. First, synthetic GPR data were generated and subsequently inverted considering different thin-layer model configurations. The resulting inversion errors when neglecting the thin layer were quantified, and then, the possibility to reconstruct these layers was investigated. Second, laboratory experiments reproducing some of the numerical experiments configurations were conducted to assess the stability of the inverse solution with respect to actual measurement and modeling errors. Results showed that neglecting shallow thin layers may lead to significant errors on the estimation of soil surface water content ($\Delta\theta$ > 0.03 $m^3/m^3$), depending on the contrast. Accounting for these layers in the inversion process strongly improved the results, although some optimization issues were encountered. In the laboratory, the proposed full-waveform method permitted to reconstruct thin layers with a high resolution up to 2 cm and to retrieve the soil surface water content with an rmse less than 0.02 $m^3/m^3$, owing to the full-waveform inverse modeling. These results suggest that the proposed GPR approach is promising for field-scale mapping of soil surface water content of nondispersive soils with low electrical conductivity and for instances when soil layering is encountered. [less ▲]

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See detailA generalized frequency domain reflectometry forward and inverse modeling technique for soil electrical properties determination
Minet, Julien ULg; Lambot, Sébastien; Delaide, Géraldine et al

in Vadose Zone Journal (2010), 9(4)

We have developed a generalized frequency domain reflectometry (FDR) technique for soil characterization that is based on an electromagnetic model decoupling the cable and probe head from the ground using ... [more ▼]

We have developed a generalized frequency domain reflectometry (FDR) technique for soil characterization that is based on an electromagnetic model decoupling the cable and probe head from the ground using frequency-dependent reflection and transmission transfer functions. The FDR model represents an exact solution of Maxwell’s equations for wave propagation in one-dimensional multilayered media. The benefit of the decoupling is that the FDR probe can be fully described by its characteristic transfer functions, which are determined using only a few measurements. The soil properties are retrieved after removing the probe effects from the raw FDR data by iteratively inverting a global reflection coefficient. The proposed method was validated under laboratory conditions for measurements in water with different salt concentrations and sand with different water contents. For the salt water, inversions of the data led to dielectric permittivity and electrical conductivity values very close to the expected theoretical or measured values. In the frequency range for which the probe is efficient, a good agreement was obtained between measured, inverted and theoretically predicted signals. For the sand, results were consistent with the different water contents and also in close agreement with traditional time domain reflectometry measurements. The proposed method offers great promise for accurate soil electrical characterization because it inherently permits maximization of the information that can be retrieved from the FDR data and shows a high practicability. [less ▲]

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See detailDevelopment of a version of GeoPEARL for the Walloon region of Belgium
Bah, Boubacar Billo ULg; Vanclooster, Marnik; Oger, Robert ULg

Scientific conference (2009, November)

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See detailHydrogeological investigations at the Membach station, Belgium, and application to correct long periodic gravity variations
Van Camp, Michel; Vanclooster, Marnik; Crommen, O. et al

in Journal of Geophysical Research (2006), 111(B10),

A comprehensive hydrogeological investigation regarding the influence of variations in local and regional water mass on superconducting gravity measurements is presented for observations taken near the ... [more ▼]

A comprehensive hydrogeological investigation regarding the influence of variations in local and regional water mass on superconducting gravity measurements is presented for observations taken near the geodynamic station of Membach, Belgium. Applying a regional water storage model, the gravity contribution due to the elastic deformation of the Earth was derived. In addition, the Newtonian gravity effect induced by the local water mass variations was calculated, using soil moisture observations taken at the ground surface (about 48 m above the gravimeters). The computation of the gravimetric effect is based on a digital elevation model with spatially discretized rectangular prisms. The obtained results are compared with the observations of a superconducting gravimeter (SG). We find that the seasonal variations can be reasonably well predicted with the regional water storage model and the local Newtonian effects. Shorter-period effects depend on the local changes in hydrology. This result shows the sensitivity of SG observations to very local water storage changes. [less ▲]

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