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Dynamiques et origines des matières en suspension sur de petits bassins versants agricoles sur schiste

Abstract : Suspended sediments (SS) are responsible for aquatic habitat degradation such as siltation of spawning gravels and increase in turbidity. They are also involved in water quality as a vector of different contaminants within river systems. Suspended sediment production increase with land-use and landscape modifications such as hedgerow suppression. The objectives of this work are, on the one hand, to describe and explain SS dynamics on small agricultural catchments and, on the other hand, to identify particle origin. This study focuses on field experiments of three catchments located in northwestern France. These catchments have similar area (<5 km²), geology (schist) and precipitation; but their bank degradation is different. SS dynamics are studied using SS concentration-discharge relationship at different time scales. SS origins is assessed by the interpretation of SS concentration-discharge relationships and by direct methods such as estimation of soil erosion rate with 137Cs, SS-sources fingerprinting. SS dynamics depend on particle availability. SS concentration-discharge relationships on Moulinet and Violettes catchments indicated that particles essentially come from in-stream processes (e.g., bank erosion, removal of deposited sediment) and from the degradation of riparian areas by cattle trampling. This conclusion was confirmed both by 137Cs measures on riparian areas and by fingerprinting SS sources. On Coët Dan-Naizin, cattle can not reach the stream because of vegetation or fences on banks; thus particles mainly come from in-stream processes alone. Territory management would suggest an arrangement that integrates cattle as a determining parameter in SS dynamics.
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Submitted on : Wednesday, October 10, 2007 - 12:52:55 PM
Last modification on : Monday, July 6, 2020 - 3:38:32 PM
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Julie Lefrançois. Dynamiques et origines des matières en suspension sur de petits bassins versants agricoles sur schiste. Hydrologie. Université Rennes 1, 2007. Français. ⟨tel-00178187⟩

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