An advanced tool for eutrophication modeling in coastal lagoons: Application to the Victoria lagoon in the north of Spain

•Development of an advanced eutrophication model for application to coastal lagoons.•The proposed model considers a total of 19 state variables.•The model considers all possible interactions between the different variables.•The model describes bio-physicochemical processes that can occur in coastal lagoons.•The model has been applied in a lagoon in the north of Spain. A mathematical eutrophication model, EnvHydrEM (Environmental Hydraulics Institute Eutrophication Model), was developed to be applied specifically to coastal lagoons. This model takes into consideration 19 state variables, including phytoplankton, carbon (total inorganic carbon and sediment carbon), phosphorus (organic phosphorus and phosphate), nitrogen (organic nitrogen, ammonia and nitrate), silica (available dissolved and particulate biogenic silica), dissolved oxygen, carbonaceous organic matter, zooplankton, bacterioplankton, detritus, iron (total and ferrous iron) and manganese (total manganese and manganous ion). EnvHydrEM also describes all possible interactions between the considered variables, showing biological and physicochemical processes that can occur in this type of aquatic systems. These are usually characterized by a series of peculiar aspects which result mainly from the complex interaction between inland and marine waters, as well as from a low hydrodynamic renewal rate. To provide an example, the EnvHydrEM model was applied to the study of the eutrophication process in the Victoria lagoon, in northern Spain. In this case study, the proposed model has proved its ability to reproduce the chlorophyll-a concentration trends in the water body. The study also concluded that the Victoria lagoon is a mesotrophic aquatic media in which silica is the most critical factor for the analysis of its eutrophication state, due mainly to the presence of diatoms.