Long-term trends in changes of the chemical composition of waters in lakes heated by electric power plants

The aim of the study was to identify trends in changes of the chemical composition of the waters of a heated lake ecosystem. Lakes Ucheńskie, Ślesińskie, Gosławslde, and the water uptake and discharge canals of electrical power plants were the subjects of the study. The waters studied were characterized by hydrocarbonate and lime salinity. Calcium and hydrocarbonate accounted for approximately 60-70% of the total concentration of dissolved ions in the waters. Changes in the overall salinity of the waters were characterized by a progressive increase of water electrolytic conductivity and increases in calcium, hydrocarbonate, and sulfate. The organic fraction was the dominant form of nutrient in the epilimnion of these lakes. The near-bottom layers were dominated by phosphate and ammonium nitrogen. Concentrations of these increased in the spring-summer period as oxygen deficits increased at the bottom. Lake eutrophication limited the availability of nitrogen and carbon to the phytoplankton. The low retention times of the water in the lakes limited phytoplankton blooms.