Impact of storms and floods episodes on primary production in an exploited coastal zone (Thau lagoon, south of France): Coupled hydrodynamic-biogeochemistry modeling approach.

Abstract : The authors collaborate within the SO RECThau (Service of Observation and Research in coastal Environment of Thau) of the OSU OREME. They find themselves here on a project of hydro-biogeochemical numerical modelling complementary of their activities of observations. Illustrated on the period of the RESTHAU campaign (November 2008), the aim is to evaluate the impact of storms and floods episodes on primary production. The coupled model Symphonie-ECO3M was implemented on a fairly original computing grid encompassing the Thau lagoon, the canals, the foreshore and open sea to the offshore zone. The hydrodynamic model is coupled to the ECO3M model based on mechanistic formulations of biological processes. The model uses 35 state variables and reproduces a complex planktonic ecosystem with several primary producers and several consumers. The biochemical cycles of the biogenic elements (C, N, P, Si) are managed by the model. Owing to field data, the November 2008 storm period was investigated. The first results show no increase in primary production during and after the storm in spite of an enrichment of the lagoon in nutrients which seems to indicate a limitation by light or temperature. The role of predation by oysters (more than 10 000 tonnes in the lagoon) is also investigated by comparing the modified model integrating this compartment with mesocosms results.