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Orléans, France

Lescure T.,3 Avenue Claude Guillemin | Lescure T.,CNRS Earth Sciences Institute of Orleans | Lescure T.,CNRS Interdisciplinary Laboratory for Continental Environments | Lescure T.,French Environment and Energy Management Agency | And 10 more authors.
Environmental Geochemistry and Health | Year: 2015

The global AsIII-oxidizing activity of microorganisms in eight surface soils from polluted sites was quantified with and without addition of organic substrates. The organic substances provided differed by their nature: either yeast extract, commonly used in microbiological culture media, or a synthetic mixture of defined organic matters (SMOM) presenting some common features with natural soil organic matter. Correlations were sought between soil characteristics and both the AsIII-oxidizing rate constants and their evolution in accordance with inputs of organic substrates. In the absence of added substrate, the global AsIII oxidation rate constant correlated positively with the concentration of intrinsic organic matter in the soil, suggesting that AsIII-oxidizing activity was limited by organic substrate availability in nutrient-poor soils. This limitation was, however, removed by 0.08 g/L of added organic carbon. In most conditions, the AsIII oxidation rate constant decreased as organic carbon input increased from 0.08 to 0.4 g/L. Incubations of polluted soils in aerobic conditions, amended or not with SMOM, resulted in short-term As mobilization in the presence of SMOM and active microorganisms. In contrast, microbial AsIII oxidation seemed to stabilize As when no organic substrate was added. Results suggest that microbial speciation of arsenic driven by nature and concentration of organic matter exerts a major influence on the fate of this toxic element in surface soils. © 2015 Springer Science+Business Media Dordrecht Source

Gay A.,3 Avenue Claude Guillemin | Gay A.,University of Tours | Cerdan O.,3 Avenue Claude Guillemin | Mardhel V.,3 Avenue Claude Guillemin | Desmet M.,University of Tours
Journal of Soils and Sediments | Year: 2015

Purpose: Sediment connectivity at the landscape scale has gained interest in the last few decades. Distributed approaches, such as topographic indices, are widely used to evaluate this connectivity. However, most of the research efforts are concentrated in mountainous areas while little work has been done in lowland areas where evidence of high connectivity has been reported. The objectives of this study are as follows: (i) to integrate landscape infiltration/runoff properties in the assessment of connectivity to account for lowland processes and (ii) to apply this approach to a large territory with both mountainous and lowland areas. Materials and methods: The topographic index of connectivity (IC) of Borselli et al. (2008) was computed for the Loire–Brittany River Basin (>105 km2). A distributed parameter (IDPR) that reflects landscape infiltration and saturation properties due to underlying geological formation characteristics is introduced. We integrated this parameter in a revised index (ICrevised) as an indicator of landscape hydrologic connectivity. Results at the pixel scale are aggregated at the watershed scale. Results and discussion: Two maps of connectivity are produced, considering the initial IC and the revised form (ICrevised). As expected, the IC gives the highest connectivity in the steepest areas and does not reflect the existing connectivity in lowland areas. On the contrary, the ICrevised computed in this study profoundly modifies the sediment connectivity values. These changes are evenly distributed over the entire territory and affected 51.5 % of the watersheds. As a result, we obtained a better correlation between calculated connectivity and the observed drainage density (which reflects the actual connections between hillslopes and rivers) in areas where slopes are gentle (<7 %). Conclusions: Topographic indices do not reflect the real sediment connectivity in lowland areas, but their adaptation by considering runoff processes of such areas is possible. The ICrevised presents an interesting perspective to define other highly connected areas at the country scale, as 17 % of the French territory is characterized by very gentle slopes with high runoff capacity. © 2015 Springer-Verlag Berlin Heidelberg Source

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