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Organisation spatiale des paysages bocagers et flux d'eau et de nutriments. Approche empirique et modélisations

Abstract : Pollution of surface water by nutrients, sediments and pesticides is a prominent issue in agricultural catchments over the world. In Brittany, the increase of intensive farming involves the use of agricultural inputs and the suppression of many hedges and wetlands between cultivated fields and stream water. This evolution is often pinned out for the responsibility of water quality degradation.
The studies conducted since the seventies show that the hydrological and hydrochemical impacts of hedges may be strong at the local scale. The first objective of this work was to study the role of hedgerows at the catchment scale. The second objective was to link the knowledge about hedge buffer functions with the knowledge about the organization and the evolution of rural landscapes resulting from agricultural activities. Three items were developed : a conceptual item to define the buffer function of landscapes, an empirical item to compare the buffer effect at the outlet of five catchments and a modelling item. Two modelling approaches were developed in the last item. First, the influence of hedges on the hydrology of a small catchment was assessed by integrating the results on the influence of hedge evapotranspiration on soil water dynamics existing at the local scale in an distributed hydrological model. Second, we
modelled landscape organization and evolution on the basis of rules of farm functioning (land-use allocation) and of farm evolution (increase of farm size and change in farming system) : the outputs of the landscape model were analyzed with two models describing the functional organization of hedgerow networks, the one for surface fluxes and the other one for subsurface fluxes.
A review has led to a typology of buffer effects of landscape structures, based on time consideration, and to the definition of the buffer effects of landscapes, integrating the effect of landscapes structures and of the physical and geomorphological characteristics of the catchments. In the framework of the empirical item, we measured a gradient of landscape buffer effect similar to the gradient of hedge density between the catchments : this stressed the co-variation of physical and geomorphological characteristics of the catchments, the types of farming systems, the type of fields and the type of hedgerow systems. Hydrological modelling showed the specific hydrological impact of hedges at the annual time scale : it is stronger during the dry years. The landscape modelling showed that a given evolution of farms has variable consequences on the buffer effect at the catchment scale.
The buffer effect on subsurface fluxes is more constant and resilient than the buffer effect on surface
fluxes, which highly depends on hedgerow network continuity.
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https://tel.archives-ouvertes.fr/tel-00007460
Contributor : Alain-Hervé Le Gall <>
Submitted on : Friday, November 19, 2004 - 1:46:50 PM
Last modification on : Thursday, February 11, 2021 - 3:04:14 PM
Long-term archiving on: : Friday, April 2, 2010 - 8:47:28 PM

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Valérie Viaud. Organisation spatiale des paysages bocagers et flux d'eau et de nutriments. Approche empirique et modélisations. Sciences de la Terre. Agrocampus - Ecole nationale supérieure d'agronomie de renneS, 2004. Français. ⟨tel-00007460⟩

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