Annual nutrients export modelling by analysis of landuse and topographic information: case of a small Mediterranean catchment

The preservation of water bodies from eutrophication implies accurate estim ation of phosphorus and nitrogen loads and the control of nutrient producti on on a catchment scale. In this paper, a simple tool for the modelling of annual nutrient loads is presented. It is implemented in ARC/INFO GIS using Are Macro Language (AML). The use of a GIS is justified as the spatial cha racteristics of the catchment area (land use, industrial wastewater locatio n) dictate water quality. The annual nutrient loads are worked out on the c atchment scale, using existing GIS routines together with specific routines developed in AML for hydrological and water quality modelling purposes. Th e catchment area is divided into hydrological subcatchments with relatively homogeneous spatial characteristics. Each subcatchment is linked to a spec ific nutrient export potential. These nutrient loads, calculated on a subca tchment-by-subcatchment basis, are conveyed to the outlet of the catchment and allow annual nutrient load estimation. A comparison with a water monito ring study is conducted to verify the adequation of modelling results for p hosphorus and nitrogen loads.