Modeling of Escherichia Coli fluxes on a catchment and the impact on coastal water and shellfish quality

International audienceThe simulation of the impact of Escherichia coli loads from watersheds is of great interest for assessing estuarine water quality, especially in areas with shellfish aquaculture or bathing activities. For this purpose, this study investigates a model association based on the Soil and Water Assessment Tool (SWAT) coupled with a hydrodynamic model (MARS 2D; IFREMER). Application was performed on the catchment and estuary of Daoulas area (France). The daily E. coli fluxes simulated by SWAT are taken as an input in the MARS 2D model to calculate E. coli concentrations in estuarine water and shellfish. Model validation is based on comparison of frequencies: a strong relationship was found between calculated and measured E. coli concentrations for river quality (r2 = 0.99) and shellfish quality (r2 = 0.89). The important influence of agricultural practices and rainfall events on the rapid and large fluctuations in E. coli fluxes from the watershed (reaching three orders of magnitude in