Un outil de modélisation intégrée du transfert des nitrates sur un système hydrologique : application au bassin de la Seine

An Integrated Modelling Tool for Nitrates Transport in a Hydrological System: Application to the River Seine Basin

¹ École des Mines de Paris, CIG, UMR Sisyphe
² INRA, SAD, Mirecourt
³ INRA, Unité d'Agronomie, Laon
⁴ UMR Sisyphe 7619, Université Pierre et Marie Curie
⁵ CNRS, UMR - 1, Meudon

Abstract

The regular increase of the nitric contamination of both groundwater and surface water has become preoccupying in the river Seine basin. A major research topic of the programme PIREN-Seine consists in developing a software for the basin-scale modelling of the transport of nitrogen from soil to surface water, accounting for its retardarion due to the residence time in soil and aquifer systems, which can be very long. Prior to software development, an original work of data processing has been performed at INRA, in space and time, concerning pedological characteristics, land use and agricultural practices, in order to determine the spatial units to be included into the model. These data are input data for the STICS software (INRA) which simulates the functioning of the soil-water-vegetation system at a daily time-step, taking into account the growth of the crops and the nitrogen and water balances. A procedure for the spatialisation of STICS at the basin scale has been developed to compute the water and nitrate fluxes at the bottom of the root zone. These fluxes are integrated into the surface and groundwater coupled model MODCOU (ENSMP), which calculates, at a daily time-step, the water balance in the hydrological system, the flow in the rivers and the piezometric variations in the aquifers, as a function of climatic data (rainfall, PET). Then, the transport of nitrates and the resulting evolution of nitric contamination in groundwater and rivers is computed owing to the compatible software NEWSAM (ENSMP). Nitrogen fluxes reaching the rivers can be used by the SENEQUE software, which simulates the water quality and the ecological functioning in the hydrographical network. In a close future, this research will be used to simulate the response of nitric contamination to various scenarios, accounting for the modification of agricultural practices or anthropogenic climate change.