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La base de données utilisée pour la présente étude rassemble des populations d’analyses de sols provenant de cinq sources correspondant chacune à une stratégie d’échantillonnage différente et à un objectif distinct. Au total, 3 929 analyses réalisées entre 1990 et 2007 ont été collectées : elles provenaient presque exclusivement d’horizons de surface de sols agricoles. Outre les concentrations en ETM, les principales caractéristiques agro-pédologiques et les coordonnées géographiques, la base de données contient également des informations sur l’occupation du sol et sur la nature du matériau parental. Dans le Nord -Pas-de-Calais affleurent des roches sédimentaires variées, souvent recouvertes par des dépôts éoliens limoneux, mais tous ces matériaux montrent des teneurs naturelles faibles en ETM. Les différentes stratégies d’échantillonnage se sont assez bien complétées et ont permis une bonne couverture du territoire régional et des diverses causes de contaminations anthropiques : aussi bien les sources diffuses que celles très ponctuelles. Ont été réalisés divers traitements tels que : statistiques régionales descriptives ; examen de la localisation des valeurs anomaliques ; cartographies mono-élémentaires par krigeage ; vision multi-élémentaire grâce à un indice numérique additif très simple. Un fort contraste apparaît entre des secteurs fortement influencés par des contaminations voire des pollutions multimétalliques (zones riveraines de l’agglomération lilloise, environs immédiats de grands sites industriels) et les zones rurales qui ne montrent pas de contaminations nettes à l’exception du cadmium apporté par la fertilisation phosphatée. Outre une vision spatiale des teneurs pour les 8 principaux éléments traces, les traitements ont permis d’avoir une bonne connaissance statistique des teneurs usuelles en stratifiant par matériaux parentaux et par petites régions naturelles. Ces « teneurs agricoles habituelles » (TAH) ainsi stratifiées peuvent être correctement estimées en considérant toutes les valeurs comprises entre le percentile 10 et le percentile 90. Ces TAH peuvent être utilisées comme valeurs de référence plus appropriées que de simples statistiques calculées à l’échelon régional ou départemental, tout particulièrement dans le cadre de l’interprétation de l’état des milieux ou pour proposer aux services santé-environnement des Agences Régionales de Santé des valeurs seuils de sélection pour prendre en compte tel ou tel élément trace dans une évaluation des risques sanitaires., The data-set used for the present study gathers analyses coming from five sources each one corresponding to a different sampling strategy and a distinct objective. In total, 3 929 analyses of surface soil horizons were collected carried out between 1990 and 2007. These were almost exclusively taken from cultivated lands. Besides the trace metal concentrations, the major agro-pedological characteristics and the geographical coordinates, the data-set also contains information relative to the land use and lithology of the parent materials. In the Nord - Pas-de-Calais region various sedimentary rocks are outcropping often overlaid by aeolian silty deposits, but all these materials show low natural contents in trace elements. The different sampling strategies complemented rather well each other and allowed a good covering of the region territory and diverse causes of anthropogenic contamination : diffuse as well as point-sourced. Have been carried out diverse data processing such as : i) region-wide summary statistics ; ii) examination of the location of outlier values ; iii) design of maps of each trace element using krigeage ; iv) multi-element view thanks to a very simple additive numerical index, etc. A marked contrast appears between areas strongly influenced by multi-metal contamination or even pollution (surroundings of the Lille urban area, lands in the close vicinity of large industrial plants) and rural territories which do not show noticeable contamination (with the exception of cadmium supplied by phosphate fertilizers). Besides a spatial view of the concentrations of soils in the main trace elements, the data processing allowed us to have good statistic knowledge of usual concentrations, especially when stratifying the data by parent material and “little natural regions”. These “usual agricultural concentrations” (UAC) can be well assessed by considering all the values included between percentile 10 and percentile 90. UAC obtained in this manner can provide local “reference values” or guidelines much more appropriate than mere statistics reckoned at theregion or the “département” scale, particularly in the framework of the approach so-called “interpretation of the state of the environment”. These values also provide a reference state for those who must evaluate possibly polluted sites and carry out health risk assessments., La base de datos usada para el estudio presente reúna populaciones de análisis de suelos que provienen de cinco fuentes que corresponden cada una a estrategia de muestreo diferente y a un objetivo distinto. En total, se colectaron 3 929 análisis realizados entre 1990 y 2007: provinieron casi exclusivamente de horizontes de superficie de suelos agrícolas. Además de las concentraciones en elementos en trazas metálicos (ETM), las principales características agro-pedológicas y las coordinadas geográficas, la base de datos contiene igualmente informaciones sobre el uso del suelo y sobre la naturaleza del material parental. En la región Norte- Paso de Calais afloran rocas sedimentarias variadas, a menudo recubiertas por depósitos eólicos limosos, pero todos estos materiales muestran pequeños contenidos naturales en ETM. Las diferentes estrategias de muestreo se completaron bastante bien y permitieron una buena cobertura del territorio regional y de diversas causas de contaminaciones antrópicas : tan las fuentes difusas que puntuales. Se realizaron diversos tratamientos como : estadísticas regionales descriptivas ; examen de la localización de valores anormales ; cartografías mono-elementarías por krigeage ; visión multielementaría gracias a un índice numérico aditivo muy simple. Un fuerte contraste aparece entre los sectores fuertemente influenciados por contaminaciones, incluso contaminaciones metálicas (zonas vecinas de la aglomeración de Lille, cercanías inmediatos de grandes lugares industriales) y las zonas rurales que no muestran contaminaciones netas con excepción del cadmio aportado por la fertilización fosfatada. Además de una visión espacial de los contenidos para 8 principales elementos traza, los tratamientos permitieron tener un buen conocimiento estadístico de los contenidos usuales estratificando por materiales parentales y por pequeñas regiones naturales. Estos “contenidos agrícolas habituales” (TAH) así estratificados pueden estar correctamente estimados considerando todos los valores incluidos entre el percentil 10 y el percentil 90. Estos TAH pueden estar usados como valores de referencia mas apropiados que simples estadísticas calculadas a escala regional o epartamental, particularmente en el cuadro de la interpretación del estado de los medios o para proponer a los servicios de salud y medio ambiente de las Agencias Regionales de Salud valores umbrales de selección para tomar en cuenta tal o tal elementos traza en una evaluación de los riesgos sanitarios.

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International audience

International audience; Since recently, geophysical methods enable the monitoring of some soil characteristics on a continuous space with a high resolution. However the interpretation of electrical measurements is difficult because the geophysical data are influenced by many soil variables, that vary, or not, with time. Our objective was then to use spatial measurements of electrical resistivity, to define zones of homogeneous electrical resistivity, to interpret them in terms of evolution of water content, and to compare them with a soil map. Our assumption was then that the time variation of electrical resistivity at the field scale was only due to the evolution of the soil moisture in our studied field. A time monitoring of the soil electrical resistivity and the soil moisture was realized during the year 2006, at four dates, both by the MUCEP device (MultiContinous Electrical Profiling), that gives measurements on a whole field area, and by local gravimetric measurements of the soil water content. Homogeneous zones were defined directly from measurements for the electrical resistivity, and after ordinary kriging for the water content. Our analysis of the spatial and temporal variability has permitted to discriminate three temporal homogeneous zones, both for electrical resistivity and the water content, that were mainly related to the soil map. The use of electrical measurements enables to directly describe the spatial and temporal evolution of soil water content at the field scale, and to describe some hydric processes, like lateral flows or upward capillary flows that would be difficult to derive from soil maps.

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National audience

National audience

National audience; At the field scale the spatial variability of the soil hydric behaviour could be described with a high resolution by data fusion between the electrical resistivity and the soil water content measurements. However, whereas many authors underline significant correlations between these two variables, the electrical measurements are also influenced by other soil variables (clay content, temperature, salinity…) through complex interactions. The electrical data interpretation is delicate and depends on soil types. In a calcareous context, we aim at showing the usefulness of the electrical method to discriminate the spatial variability of the soil water content at the field scale. A time- monitoring of the soil water content and the electrical resistivity was realised . The spatial variability is analysed and the soil hydric units are defined. They are finally compared to the soil units.

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EUROPEAN SOIL BUREAU RESEARCH REPORT NO. 20; International audience

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