Long term changes in the quality of the aquatic environment of thermally polluted Lake Licheńskie, Central Poland

Study region: Central Europe, Gniezno Lake District, Poland Study focus: The purpose of this study is to depict and explain long-term trends in surface water temperatures (LSWT) and chemical composition in Lake Licheńskie (LLi), which since 1960s has been involved in a cooling system of two electric power plants (PP) and thus has been prone to thermal pollution (TP). For the analyses we used 24-year long stationary monitoring and satellite data. New hydrological insights for the region: We estimated that LLi was 3.81°C warmer than natural lakes in the region and demonstrated that the TP displayed spatial and seasonal variability. The data shows that owing to a reduction in the PP activity the LSWT has constantly been decreasing at a rate of 0.09°C·y−1. Because, the lake has also been supplied with saltwater and highly alkaline effluents from nearby brown coal mine, LLi has been prone to salinization and alkalinization. The former process is still ongoing but alkalinization is declining, which is interpreted as a self-recovery of the lake triggered by a reduction in brown coal mining in the region. The knowledge of environmental conditions in the lake as well as its long-term changes is crucial for developing lake management strategies in the face of planned incorporation of the lake in a cooling system of the new nuclear power plant in the vicinity of the lake.