Soil occupation and water quality in the Gascony sandy ecosystem

The development of intensive corn cropping and the increase in deforestation made authorities concerned about decay in landscape, soil erosion, aquifer contamination, and quality of fresh-water lakes and bays in Gascony. The spatial distribution and the impact of upstream activities must be assessed in order to achieve a sustainable management of the area. The watershed appears to be the ideal scale for this purpose. Since 1996, hydrological and chemical surveys of two watersheds, the first one forested and the second one including an intensive farming area, clearly show that nutrients fluxes are connected to soil occupation and practices. A typology of practices in forested and cropping areas was realised in order to be spatialised on a larger scale. Major causes of nutrient losses were identified. The role of buffer zones, such as reservoirs and forested sections, in reducing non-point pollution from upstream cropping areas was studied.