Circulation and nutrient modeling of Thermaikos Gulf, Greece

Thermaikos Gulf is considered to be one of the most polluted coastal zones in Greece. It is the final receptor of both municipal and industrial wastewaters from the city of Thessaloniki and of two heavily polluted rivers, Axios and Aliakmon. Nutrient enrichment and consequent eutrophication is the primary water quality issue of Thermaikos. The mathematical model WASP 6.0 was used to simulate the hydrodynamics, nutrient dynamics and phytoplakton evolution in the gulf. The model is a physical-based model that compartmentalizes the water body into high dispersivity, uniform concentration compartments. It then performs mass balances on water quantity and quality. In addition to the hydrodynamics, the model can simulate the carbon, oxygen, nitrogen, phosphorous and plankton concentrations in the water body. Monthly hydrologic and water quality fluxes from 1997 to 1998, inputs to the gulf and seasonal nutrient surveys in the gulf were used to calibrate nutrient dynamics. The gulf was compartmentalized into 12 compartments, six were horizontal and two were vertical. Salinity data were used to calibrate the hydrodynamic variables of the model. Model calibration was conducted by minimizing the root mean square error between field observations and model simulation. The model was able to capture the variation of salinity and nutrient concentrations. The results showed the importance of Thessaloniki effluents to the Thessaloniki Bay and Gulf and the Axios and Aliakmon River loads to the degree of eutrophication of the entire gulf. The model can be used to assess management scenarios to improve the water quality of the gulf.