Ecosystem modelling: Towards the development of a management tool for a marine coastal system part-II, ecosystem processes and biogeochemical fluxes

Pagasitikos gulf is a semi-enclosed basin highly influenced both by anthropogenic activities (inflow of nutrients at the north and west parts) as well as by water exchange between the gulf and the Aegean Sea at its south part (Trikeri channel) resulting in the development of functional sub-areas within the gulf. Thus the inner part is characterised by eutrophic conditions with sporadic formation of harmful algal blooms whilst the central part acts as a buffer with mesotrophic characteristics influenced by the outer area. In a companion paper, the circulation fields and the development of water masses in the Pagasitikos gulf were explored. The aim of this study is to investigate the interactions between the physical and biogeochemical systems in the Pagasitikos gulf by coupling advanced hydrodynamic and ecological models. The simulation system comprises two on-line coupled sub-models: a three-dimensional hydrodynamic model based on the Princeton Ocean Model (POM) and an ecological model adapted from the European Regional Seas Ecosystem Model (ERSEM) for this specific ecosystem. After a model spin up period of 10 years, the results from an annual simulation are presented. Emphasis is given to the description of the spatial and temporal variability of the ecosystem parameters as well as to the relationship between physical forcing and the evolution of the ecosystem along with other factors affecting the nutrient cycling and primary production. A cost function is used for the validation of model results with field data. Simulation results are in good agreement with in-situ data illustrating the role of the physical processes in determining the evolution and variability of the ecosystem, as well as highlighting the potential usefulness of the model as an operational tool to support environmental management decisions.