Forêt et ressource en eau: Étude de deux Bassins versants en sol sableux (Landes de gascogne)

Abstract

To gain a better understanding of nutrient loading and transfers in sandy soils and provide elements for a sustainable management of the area, two representative watersheds of the Gascony sandy ecosystem - one forested, the "Tagon", and the other mixed forest-and-crops, the "Arriou" - were instrumented and monitored from 1996 to 2002. The weekly hydrological and chemical recordings show that nitrogen produced by the forested watershed is found mainly in organic form, while, in the mixed watershed, large amounts of nitrates form. Using special equipment, a flood study of two streams was conducted showing increased nutrient loading, particularly in autumn and winter. Agricultural and forestry practices were analysed on a larger scale and the results confirm the two studied areas as representative. Surveys showed that in the farming areas practices have become highly intensive whereas the soils and freshwaters are classified as sensitive. Current forestry practices are such that the forest continues to have a regulating function, but trends in forest management towards more intensive scenarios for maritime pine must be monitored, particularly as the nutrient absorption capacity of sandy ecosystem streams is weak.