Coupled SWAT-RIVE model to improve biogeochemical fluxes assessment in drainage network: the case of the Vienne watershed (France)

Water resource demands are expected to increase with climate change and demographic growth. To identify effective levers for action to guarantee access to water, in sufficient quantity and of good quality, there is a need to determine hydrologic and contaminant stocks and flows in order to anticipate their evolution. A model is a useful tool to assess these stocks and fluxes at different spatial and temporal scales. The SWAT model (Soil and Water Assessment Tool) is a semi-distributed hydrological model successfully applied around the world, that simulates transfer of biogenic elements from land to river at the scale of watersheds. However, we need to improve the representation of biogeochemical in-stream processes currently modeled by the calibrated QUAL2E in SWAT in order to quantify spatial and temporal dynamics of nitrogen, organic carbon and suspended sediments fluxes in addition to water flow. The mechanistic ecological RIVE model has been chosen to represent in-stream biogeochemical processes of a river system without calibration. The coupled SWAT-RIVE model is applied to the medium-sized agricultural Vienne watershed (France). The results show that such a coupling is able to improve the capability of SWAT to estimate biogeochemical fluxes in the drainage network. This will strengthen the role of buffer zones, e.g. wetlands in the fate of in-stream contaminants (e.g. nitrate).