Résumé
This paper presents a model which aim is to study the effects of land use and human activities on the nitrogen loads produced at the outlet of a catchment, during a rain event. The POL model is based on a simple conceptual approach and involved a reduced number of parameters. A spatial segmentation of the catchment is determined according to topography, land use and human activities. The catchment is subdivided into subcatchments and associated reaches. Land use, determined by remote sensing, and point source pollution are integrated on GIS tool ARC-INFOÒ to characterise each model unit (subcatchment or river reach). Two main processes are taken into account : nitrogen production on the subcatchment surfaces and transport along the river reaches. A flexible modelling environment is used to conceptualise, simulate and optimise the POL model (VENSIMÒ software). This modelling approach is conducted on the Salaison catchment, (53 km²), located in the South of France.