Simulation of transport & fate of suspended matter along the coast of Agathoupolis (N. Greece)

Abstract

Modelling of algal bloom in a coastal basin constitutes a useful tool for diagnostic and prognostic purposes related to environmental and ecological problems in the greater area of the basin. This paper focuses on the transport of suspended harmful phytoplankton cells, after an episode of an algal bloom, examined by means of mathematical modeling. The case of Thermaikos Gulf was used for the application of the simulation. Thermaikos Gulf is a semi-enclosed sea located in the northwestern Aegean Sea. The present work aims at the development and application of a hydro-biological model for the study of phytoplankton growth and dispersion after an episode of algal bloom in Thermaikos Gulf. The necessary hydrodynamic information over the area of the gulf was obtained by the application of a two-dimensional, hydrodynamic model, directly coupled with a transport model, for the simulation of the fate of the harmful phytoplankton cells. The model describes hydrodynamic processes such as advection and dispersion as well as biological processes such as cell growth and division. The mechanical processes were described by the conservation equations of mass and momentum, as well as the equations for the movement of the particles based on the Random Walk Simulation. The biological process of cell growth rate are described as a function of temperature, light and nutrients, and embodied to the simulation as input data for the model runs, while the biological losses are simulated through the removal of particles randomly selected. Concerning the present application, the structure and the calibration of the model were based on the mathematical simulation of a real algal bloom episode in Thermaikos. In more detail, the dispersion of dinophysis recorded in Thermaikos Gulf after an algal bloom at 10th of January 2000, and their distribution in the marine environment of the Gulf three weeks days later, was studied. The results of the simulations were very close to reported values from field measurements and confirm the value of the presented methodological approach. Concerning the particular application it seems that after a phytoplankton bloom at the northeast coasts of Thermaikos Gulf, concentrations of harmful algal cells, reach to the northwest and west coasts of the gulf where the largest part of the mussel culture of Greece lies. Furthermore the harmful algal cells seem to reach the bathing coasts of the western Gulf. Finally the environmental scope of the model was fulfilled by detecting the distribution of the harmful algae concentrations in the Thermaikos basin under the influence of the prevailing wind conditions over the area of the Gulf. The hydro-biological model described here can also be applied in different coastal basins with known topographic characteristics, so that prevention measures can be taken on time.