A simulation model for the description of a eutrophic system with emphasis on the microbial processes

A mathematical model was constructed trying to describe the dynamics of a coastal eutrophic system, with emphasis on the processes of phytoplanktonic exudation and bacterial mineralization. The model is two-dimensional with two compartments, the one characteristic of eutrophication and the other one of oligotrophy. Five state variables were chosen characterizing eutrophication, phytoplankton, bacteria, dissolved organic carbon (DOC), nitrate and ammonia concentration. The nutrient and organic load from sewage outfalls was also estimated from data available for the city of Mytilini. For the evaluation of the model, data available for the coastal area of Mytilini, Lesvos were used, collected from April 1991 to December 1993. A general pattern of low values in winter and higher in summer was predicted for phytoplanktonic carbon, whereas bacterial populations showed a significant seasonality with low numbers in winter time and early spring and higher in late summer and autumn. The model indicated close dependence of bacterial and phytoplanktonic growth and emphasizes the importance of eutrophic conditions in the survival and growth of the marine microbial flora. This model seems to be a useful methodological tool for the evaluation of different scenaria concerning water quality in coastal management studies.