Modelo de um sistema eutrófico: fluxo dos nutrientes e sinecologia das populações planctônicas

Abstract

Based 011 the information obtained from the Gulf of Fos, France, we propose herewith a generalized model to characterize the physical, chemical and biological parameters and their inte"elationship in the eutrophic coastal system. This system is characterized by having high concentration of suspended materiais, especially the mineral fraction (C/N> 30). Nutrients concentrations are very high, except in diluted basins. The N-N03/P-P04 ratio is usually low, due to the preferential assimilation of nitrates and the presence of polypholphates from sewage waters. The concentrations of phaeopigments are always high (more than 50%), due to the mortalities of freshwater originated phytoplankton, the resuspension of dead vegetal materiais, and the grazing of zooplankton. We noted in diluted water of eutrophic S)'stem the biomass is high, but the dive,sity is relat.-ived low, among adapted cells with low " ene1'1(etic charge". Whereas in oceanic water, the biomass ia less, the diverstty and energ'etic charge are increasing. J'his may indica te that phytoplankton commumties have to make an elfort to grow and duplicate. In comparing zooplankton populations from eutrophic to oligotrophic waters, biochemical diferentiations were observed for a SIlme species, which may due to the difference in SIllinities and the presence of chemical pollutants.