RESUMO
The migration of metals and metalloids between bottom sediments and water and the other way round is a complex process. Understanding those mechanisms is essential for recognizing transformations taking place in water reservoir ecosystems. The objective behind the following study was to define time and spatial correlations in the changes in total concentrations of selected elements (Cr, Zn, Co, Mn, Cu, Ni, Pb, As, Ba, Sb, Sr and V) in waters and bottom sediments from two water reservoirs located in Upper Silesia (Poland), i.e., Plawniowice and Dzierzno Male. The research was carried out to demonstrate whether the bottom sediments deposited in the discussed reservoirs could pose an environmental threat due to the possible release of toxic metals and metalloids into the pelagic zone. The obtained results constitute material helping to describe the bioavailability of particular elements. They also expose the existing environmental threats for such water reservoirs and their users.