Modelling the impact of microbial pollution discharge in West Cotentin coast (France)

摘要

With increased demands on coastal activities, microbial contamination of surface water isrnan emerging public health concern for populations using those waters for recreational orrnshellfish farming activities. Sewage effluents, failing septic system, runoff from farmrnfeedlots and agriculture lands are important sources of contamination. Fecal levels inrncoastal waters are often peak after a major rainfall event. The episodic nature of theirrnorigin and the transience of the receiving water response make the modeling of fecalrncontamination events particularly challenging. To assess the impact of microbial fluxesrnand to achieve water quality goals, a water quality model has been developed in the westrnCotentin coast (Normandie, France).rnA two-dimensional hydrodynamic model with the AGRIF (Adaptative Grid Refinement inrnFortran) package (75 m mesh size), was built to simulate the current and dispersion inrnthis sector, which includes areas uncovered at low tide. The model was run to describernthe hydrodynamic features, including decay rates to simulate microorganism behaviour.rnThe model was validated by simulating spatial and temporal dynamics for dry weatherrnconditions and rainfall events by comparing the calculated concentrations to a large datarnbase from shellfish survey monitoring. Using this model, different scenarios werernsimulated to estimate the critical faecal loads. This study aims to understand and to solvernthe local contamination in recreational and shellfish farming areas and thus to achievernthe European Directives.