Agricultural diffuse pollution in a chalk aquifer (Trois Fontaines, France): Influence of pesticide properties and hydrodynamic constraints

International audienceThe characterization of the transfer of pesticides to and in groundwater is essential for effective water resource management. Intensive monitoring, from October 1989 to May 2006, of a weakly karstified chalk aquifer system in a 50 km2 agricultural catchment, enabled the characterization of the temporal variability of pesticide concentrations in the groundwater of the main outlet. Atrazine and its metabolite deethylatrazine were quantified 394 and 393 times in 476 samples with concentrations ranging from the quantification limit (0.025 μg L−1) to 5.3 and 1.86 μg L−1, respectively. This common presence, compared to the rare detections of isoproturon (in 108 of 476 samples), the pesticide most widely used in the catchment during at least the past decade, highlighted the significant effect of pesticide properties in the time series of concentrations observed in the groundwater. The use of geochemical tracers (nitrate, chloride) analysed in the groundwater and the hydrodynamic monitoring of the system (discharge, water levels) enabled identification of various infiltration mechanisms governing the functioning of the system. The hydrodynamic study showing that the relative contribution of the infiltration mechanisms varies with time, made it possible to explain major variations observed in the pesticide-concentration time series recorded at the spring

Report on the tracer tests (experimental setup, results and interpretation)

Tracer experiments were performed in the Brévilles test site in order to highlight vertical variations in groundwater fluxes related to vertical variations hydraulic conductivity, to estimate contaminant travel time from several locations in the catchment to the springs and to identify transport processes affecting the fate of solutes in the saturated part of the aquifer. Following a first tracer experiment with uranine and sulforhodamine G in 2003, four tracer injections were performed in November 2005 in different piezometers, using uranine, sulforhodamine B, iodide and lithium. Tracer concentrations were monitored in the injection wells and at the basin outlet (spring and gauging station). Using the FVPDM method, concentration evolutions monitored in the injection wells allowed one to estimate local Darcy fluxes. At the basin outlet, only two tracers were recovered. Analyses of breakthrough curves confirm the stratification of the aquifer with more permeable levels in the lower part. They also suggest the probable occurrence of vertical interactions within the aquifer.AquaTerra - Integrated Modelling of the river-sediment-soil-groundwater system; advanced tools for the management of catchment areas and river basins in the context of global chang

Natural transformation of chlordecone into 5b-hydrochlordecone in French West Indies soils: statistical evidence for investigating long-term persistence of organic pollutants

International audienceChlordecone (CLD) was an organochlorine insecticide whose previous use resulted in an extensive pollution of the environment with severe health effects and social consequences. A closely related compound, 5b-hydrochlordecone (5b-hydroCLD), has been searched for and often detected in environmental matrices from the geographical area where CLD was applied. The current consensus considered that its presence was not the result of a biotic or abiotic dechlorination of CLD in these matrices but rather the consequence of its presence as impurity (synthesis by-product) in the CLD released into the environment. The aim of the present study was to determine if and to what extent degradation of CLD into 5b-hydroCLD occurred in the field. To test this hypothesis, the ratios of 5b-hydroCLD and CLD concentrations in a dataset of 810 soils collected between 2006 and 2012 in Martinique were compared to the ratios measured in 3 samples of the CLD dust commercial formulations applied in the banana fields of French West Indies (FWI) and 1 sample of the technical-grade CLD corresponding to the active ingredient used in such formulations. Soil data were processed with a hierarchical Bayesian model to account for random measurement errors and data censoring. Any pathway of CLD transformation into 5b-hydroCLD occurring over the long term in FWI soils would indeed change the ratio of 5b-hydroCLD/CLD compared to what it was in the initially applied formulations. Results showed a significant increase of the 5b-hydroCLD/CLD ratio in the soils-25 times greater in soil than in commercial formulations-which suggested that natural CLD transformation into 5b-hydroCLD over the long term occurred in these soils. Results from this study may impact future decisions for the remediation of the polluted areas

Prédiction des propriétés de rétention en eau des sols d'un bassin versant à l'aide de fonctions de pédotransfert : influence de la densité apparente et de la teneur en éléments grossiers

L'objectif est d'étudier la qualité de l'estimation des propriétés de rétention en eau faite à l'aide de fonctions de pédotransfert (FPT) pour les sols d'un bassin versant de 250 hectares. Ce bassin versant, situé à proximité de Mantes-la-Jolie, au nord-est de Paris, possède des sols limoneux à limoneux-argileux profonds sur la moitié de sa surface, l'autre moitié correspondant à des sols caillouteux. Après une prospection pédologique détaillée, 15 horizons types ont été définis (Tableau 1), puis 22 unités typologiques de sol (UTS) correspondant à la superposition de plusieurs horizons types et enfin 11 unités cartographiques de sols (UCS) regroupant plusieurs UTS (Tableau 2). Les propriétés de rétention en eau des horizons types ont été déterminées au laboratoire pour 8 valeurs de potentiels variant de –10 à –15000 hPa et, en parallèle, estimées à l'aide des FPT proposées par Hall et al. (1977), Jamagne et al. (1977), Rawls et al. (1982), Vereecken (1989), Bastet (1999) et Bruand et al. (2002) pour des valeurs de potentiel appartenant à ce même domaine. L'aptitude des FPT à rendre compte des variations des propriétés de rétention en eau mesurées pour les horizons types est très variable selon les FPT considérées (Tableau 4). Comme d'autres études l'ont déjà montré (Bastet, 1999, Tietje et Tapkenhinrichs, 1993, Wösten et al., 2001), la proximité géographique de la zone d'étude par rapport à celles ayant servi de base aux FPT et la similitude des matériaux parentaux sont des éléments importants à prendre en compte pour apprécier l'aptitude potentielle de FPT à estimer les propriétés de rétention en eau de sol. Une classification par texture, ou par texture et densité apparente, préalablement à l'établissement de FPT, permet d'améliorer la qualité des estimations. La texture et la densité apparente apparaissent donc comme des grandeurs déterminantes pour estimer correctement les propriétés de rétention en eau des horizons de sols étudiés. Toutefois, la densité apparente à l'échelle de l'horizon peut conduire à prendre en compte un volume de pores qui ne contribuent pas à la réserve en eau du sol, car de trop grande taille, et donc conduire certaines FPT à surestimer largement les valeurs de teneurs en eau. Pour les sols qui possèdent des éléments grossiers, dont la présence n'est pas prise en compte par les FPT, une correction des teneurs en eau mesurées et calculées, visant à les exprimer par rapport à la seule fraction fine (< 2 mm) des horizons, ne permet toutefois à aucune FPT de donner des résultats satisfaisants pour les sols caillouteux. Ces sols caillouteux, le plus souvent peu épais, sont ceux pour lesquels la mesure des propriétés de rétention en eau demeure la plus difficile à obtenir, aucune méthodologie adaptée n'étant disponible à l'heure actuelle

Intercomparison of Flow and Transport Models Applied to Vertical Drainage in Cropped Lysimeters

International audienceThe vertical water flow, heat flow and transport of the herbicide methabenzthiazuron were monitored for 627 days in lysimeters sampled at a field site close to the research centre Jülich, Germany. During this period the lysimeters were cropped with winter wheat, winter barley and oat. The models TRACE, MARTHE, ANSWERS and MACRO were applied to the lysimeter data with the scope of upscaling local scale process understanding for regional scale. MARTHE and TRACE solve the 3-d Richards' equation for variably saturated water flow. MACRO is a 1-d model based on the Richards' Equation and accounting for preferential flow in the unsaturated zone, while ANSWERS is a regional scale capacity based watershed model. Measurements of soil moisture, evapotranspiration, drainage, soil temperature, pesticide residues and leaching are used for comparison with model results. Although the adopted models differ in terms of model concepts, the use of model performance indices proved a proper simulation of water flow for all models. The heat flow is also well described with ANSWERS, MARTHE and MACRO. Larger deviations were found between model results and measured pesticide transport. An inadequate reproduction of the measured MBT degradation was found for the available model input parameters. A very small amount of MBT leaching, observed in the measurements, was only reproduced with MACRO after strong calibration. In other respects only plant parameters were calibrated. Calibration of the crop conversion factor used for scaling of the potential evapotranspiration was found to be a crucial parameter for the adequate description of the water balance by the models

Analysis of biofilm-nanoparticles interaction using microscopy (fluorescence, MEB, STEM, MET, EDS)

International audienceAmong biofilm's properties, the ability to interact with/catch pollutants can have applications in bioremediation. Here, biofilm interactions with metals (as iron nanoparticles (NanoFer 25S)) was evaluated using various approaches in microscopy. For this, biofilm growth, sampling, labelling and treatment were developed for each type of microscopy to access the surface or inside of the biofilm, biofilm composition, and metal location. Multispecies biofilms were grown on sand or in PVC tubes inoculated with aquifer water spiked with a nutritive solution to enhance denitrification, and then put in contact with nanoparticles. According to the targeted microscopy, biofilms were (i) sampled as flocs or attached biofilm, (ii) submitted to cells (DAPI) and/or lectins (PNA and ConA coupled to FITC or Au nanoparticles) labelling, and (iii) prepared for observation (fixation, cross-section, freezing…). Fluorescent microscopy revealed that nanoparticles were embedded in the biofilm structure as 0.5-5µm size aggregates. SEM observations also showed NP aggregates closed to microorganisms but it was not possible to conclude a potential interaction between nanoparticles and the biological membranes. STEM-in-SEM analysis showed NP aggregates could enter inside the biofilm over a depth of 7-11µm. Moreover, microorganisms were circled by an EPS ring that prevented the direct interaction between NP and membrane. TEM(STEM)/EDS revealed that NP aggregates were co-localized with lectins suggesting a potential role of exopolysaccharides in NP embedding. The combination of several approaches in microscopy is thus a good tool to better understandi and characterize biofilm/pollutant interaction

Documented spatial data set containing the subdivision of the basins into groundwater systems and subsystems, the selected locations per subsystem and a description of these sites, available data and projected additional measurements and equipment

The establishment of tools for trends analysis in groundwater is essential for the prediction and evaluation of measures taken within context of the Water Framework Directive and the draft Groundwater Directive. This report describes the spatial data sets which will be used for the purpose of detection, aggregation and extrapolation of temporal trends in groundwater quality. Trend analysis methods will be applied and tested at various scales and in various hydrogeological situations. The report contains a description of the studied sub-basins in TREND 2, including information on hydrogeology, land use and pressures, available data and projected additional measurements. Major differences between the sub-basins and the data sets are described to examine consequences for the work on trend detection. One of the challenges for TREND 2 is to define criteria for the application of various statistical and deterministic trend approaches for a range of hydrogeological conditions, spatial scales and types of groundwater monitoring. An overview of these conditions, scales and monitoring types is provided in the present report.FP6 Integrated Project AquaTerra Integrated Modelling of the river-sediment-soil-groundwater system; advanced tools for the management of catchment areas and river basins in the context of global change (Project no. 505428 - GOCE

Décontamination in situ de sols de bananeraie contenant de la chlordécone - Résultats sur nitisol de la plaine du Lamentin

Parmi les voies possibles de décontamination des sols chargés en chlordécone (CLD), les experts réunis aux Antilles en mai 2011 avaient conclu que le procédé de In Situ Chemical Reduction (ISCR) offrait un potentiel d\u27application à court/moyen terme (Clostre et al., 2010). Des travaux en laboratoire (Dictor et al., 2011Mouvet et al., 2011) ont montré que six mois de traitement par ISCR avec l\u27amendement Daramend® permettent de diminuer de 74 % la teneur en CLD du nitisol, un des principaux types de sols antillais concernés par ce type de contamination. Pour valider ces données de laboratoire, une étude de terrain est en cours sur une parcelle de bananeraie dans la plaine du Lamentin au nord-est de Fort-de-France, Martinique

Influence de la variabilité spatiale de différentes caractéristiques du milieu aux échelles de la parcelle expérimentale et du bassin versant hydrogéologique sur la contamination d'un aquifère sableux par les phytosanitaires

Ce travail concerne la contamination par les phytosanitaires d'un aquifère sableux (Val d'Oise) dont l'aire d'alimentation est de 250 ha. Après avoir étudié le fonctionnement hydrodynamique du sous-sol et délimité le bassin versant, les propriétés hydriques et les stocks de carbone organique des sols ont été spatialisés à l'échelle du bassin, afin de pouvoir modéliser ultérieurement le transport de pesticides. La détection de l'acétochlore (ACT) et de ses 2 principaux dérivés (ESA et OA) dans les horizons profonds de 2 sols contrastés et caractéristiques du bassin a montré que ces composés ont un potentiel réel de contaminer la nappe souterraine. Le suivi de la qualité de l'eau souterraine en 8 points de la nappe a montré qu'aucune contamination par l'ACT et ses 2 dérivés n'a encore été quantifiée, contrairement à l'atrazine et la DEA présentes à l'exutoire à des concentrations supérieures aux normes de potabilité malgré l'arrêt de l'application d'atrazine depuis avril 1999.ORLEANS-BU Sciences (452342104) / SudocSudocFranceF