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Mécanismes hydrologiques et hydrochimiques impliqués dans les variations saisonnières des teneurs en nitrate dans les bassins versants agricoles. Approche expérimentale et modélisation

Abstract : Nitrate concentrations in streamwater of agricultural catchments on low permeable bedrock exhibit dfferent seasonal patterns. Seasonal variations are usually characterised by higher nitrate concentrations in winter than in summer. However, intermediate or inverse cycles with higher nitrate concentrations in summer are sometimes observed. This work aims to identify hydrological and hydrochemical processes involved in seasonal variations of stream nitrate concentrations in agricultural catchments. Study is based on the caracterisation of hydrological and hydrochemical behaviour of two small catchments contrasted by their seasonal cycle (Kerbernez and Kerrien catchments, Brittany, France). A field study and a modelling approach were carried out to investigate physical and chemical properties of end-members contributing to stream discharge. For Kerrien catchment, the contribution of high subsurface flow with high nitrate concentrations during high water periods and active denitrification during low water periods explained the higher streamwater nitrate concentrations in winter than in summer. For Kerbernez catchment, the high contribution of groundwater with high nitrate concentrations smoothed or inverted this trend. Model results show that water fluxes in catchments are sensitive to spatial patterns of hydraulic conductivity more than geometry of the weathered aquifer. Moreover, seasonal cycles of nitrate concentrations in the stream are partly controlled by spatial distribution of nitrate in groundwater and to denitrification. Groundwater response time to variations of nitrate concentration in the recharge water is quicker for Kerrien catchment, but remains quite long for the two catchments.
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https://tel.archives-ouvertes.fr/tel-00003939
Contributor : Alain-Hervé Le Gall <>
Submitted on : Wednesday, December 10, 2003 - 2:48:43 PM
Last modification on : Monday, July 6, 2020 - 3:38:31 PM
Long-term archiving on: : Monday, September 20, 2010 - 11:36:18 AM

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  • HAL Id : tel-00003939, version 2

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Charlotte Martin. Mécanismes hydrologiques et hydrochimiques impliqués dans les variations saisonnières des teneurs en nitrate dans les bassins versants agricoles. Approche expérimentale et modélisation. Hydrologie. Université Rennes 1, 2003. Français. ⟨tel-00003939v2⟩

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