CHEMICAL CHARACTERISTICS OF AETOLIKO LAGOON, GREECE, AFTER AN ECOLOGICAL SHOCK

A series of chemical parameters were studied in the water, Particulate matter and sediments of Aetoliko lagoon, a wetland in western Greece, after an ecological impact at the end of November 1990, which resulte d in massive death of fish. The permanent anoxic conditions in the dee per water layer of the lagoon, with the simultaneous formation of hydr ogen sulfide, are the main characteristics of the system. The dramatic reduction of the dissolved oxygen in the surface water which was subs tituted by the hydrogen sulfide of the near bottom water layer caused the sudden death of organisms. This phenomenon also affected the nutri ents. Ammonia was the main nitrogen form; phosphates and silicates wer e concentrated in near bottom waters, and the concentrations of nitrat es and nitrites were much lower in December than 3 months later in the surface waters. The behaviour of trace metals also indicated that in the extraordinary conditions studied, the main mechanisms of transport of metals among the main phases of the system (dissolved-particulate- sediments) were severely disturbed.