Résumé
► An estuary (Senegal River) is studied with a coupled 3D biogeochemical model. ► New mechanistic formulations for some biogeochemical processes are proposed. ► Marine and freshwater organisms are distinguished in the model. ► Salinity drives freshwater organisms distribution along the estuary. ► Failure to take account of the osmotic stress can give rise to substantial errors.
This paper presents the outline of an estuary modeling study encompassing a study of the biogeochemical model on its own. It includes a preliminary validation of the new mechanistic features using mesocosm data, and a study of a coupled physical and biogeochemical model of the Senegal River Estuary (SRE) from flood to low-water conditions. The originality of this work is that it distinguishes the marine and freshwater origins of some of the organisms modeled and includes additional mortality terms owing to the osmotic stress experienced by the freshwater organisms. The mechanistic model implemented in the Eco3M modelling tool, and partially designed for this study, succeeded in representing the dynamics of the planktonic food web in two mesocosm experiments and in the SRE under very different conditions using a single set of model parameters. Among the important results, it reveals that distinguishing between marine and freshwater origins provides substantial additional information on the distribution of organisms along the estuary. Finally, failure to take account of the osmotic stress and the origin of the organisms can give rise to substantial errors in the calculation of the biomass in the SRE.