Ecological risks of dammed reservoir waters using the example of the Turawa Reservoir in southern Poland

Abstract A study of the ecological potential and the chemical pollution of the Turawa Reservoir (southern Poland), as well as an assessment of the pollution of its recharge waters, was carried out between 2019 and 2021. Four research teams took part in the study. The reservoir was chosen because of the eutrophication process that has been ongoing for several decades. Phytoplankton, phytobenthos and macrozoobenthos were surveyed as part of the ecological potential assessment. Analysed indicators were: BOD 5 , COD Cr , nitrogen concentrations (Kjeldahl nitrogen TKN, ammonium nitrogen NH 4 -N, nitrate nitrogen NO 3 -N and total nitrogen TN) and phosphorus (orthophosphate phosphorus PO 4 -P and total phosphorus TP), as well as conductivity and water pH. Using ion chromatography, the ionic composition (F − , Cl − , Br − , NO 2 − , NO 3 − , PO 4 3− , SO 4 2− , Na + , NH 4 + , K + , Mg 2+ , Ca 2+ ) and heavy metal concentrations (Cr, Ni, Zn, Cu, Cd, Pb) of the basin waters and the waters supplying the basin were determined. Coliforms, faecal enterococci and Salmonella spp. were also assessed. The condition of the reservoir water was assessed as poor. The poor quality of the water supplying the reservoir, and the bottom sediments, in which large quantities of, among other things, nutrients and heavy metals have accumulated over the years, have been identified as the cause. A factor related to biomass accumulation was also identified. During the vegetation cycle, due to biochemical processes taking place, the oxygen and nutrient indicators can be significantly influenced. The problem outlined characterises most European dam reservoirs, especially shallow reservoirs with low thermal stratification.