How should agricultural practices be integrated to understand and simulate long-term pesticide contamination in the Seine river basin?

Abstract : Modelling long term pesticide transfer to river at the catchment scale is still difficult due to a lack of knowledge about agricultural practices and non-adapted field observation. The Orgeval experimental catchment was first investigated to validate a modeling approach. Beside pesticide practices investigated over 20 years, directly collected from farmers, monthly integrated river samples were ana-lyzed for 10 years. To explicitly integrate agricultural practices and crop rotation, the crop model STICS was adapted to simulate pesticide transfer in soil. Annual load simulations were compared to observed pesticide fluxes in river. In order to simulate the contamination of groundwater, STICS-Pest model was coupled to the hydrogeological model MODCOU. Results are discussed at the sub-basin scale in relation to available data. To upscale the approach at the Seine river basin scale, other strategies need to be developed.