WATER QUALITY EVALUATION IN LAKES OF GREECE

Abstract

Recent limnological investigations carried out by the Institute of Inland Waters in Greece, have provided information on the morphological features of the natural lakes, their physicochemical characteristics and nutrient framework. With regard to the waterbodies' uses, water quality, trophic status and the natural background trophic level have been evaluated. Based on the available physical, chemical and biological parameters the Greek lakes could be categorized into:-Warm, monomictic and deep lakes with oligotrophic to oligomesotrophic and mesoeutrophic conditions mainly affected by non–point sources of nutrients.-Dimictic and shallow lakes with eutrophic to hypertrophic situations due to sewage discharges directly into the basin and oligomesotrophic with natural and agricultural enrichment of their waters.-Warm, monomictic and shallow lakes with eutrophic to hypertrophic conditions resulting mainly from agricultural runoffs and point sources of pollution. High concentrations of ammonia, nitrate and phosphate are found in many lakes, while anaerobic hypolimnia are usually encountered in the shallow ones. The phosphorus is the main factor responsible for the eutrophication processes because it is the limiting factor in most examined lakes. The phosphorus, retention coefficient, loading and its permissible level have been also calculated in some of the Greek lakes. The oscillations of the water level, the runoffs from agricultural activities and the wastewater discharges, have an increasing deleterious effect on the water quality and interfere directly with the uses of water, such as fishery, irrigation, amenities, etc.