Analysis of the Physicochemical Quality of Water Within the Hydropower Plant on the Ślęza River in Wrocław, Poland

The aim of the article was the analysis of the physicochemical quality of water within the hydropower plant on the Ślęza River in Wrocław (south-west Poland) in the context of the European Union's classification of water quality, as well as an assessment of the potential impact of hydropower plants on this quality. The study uses the results of monthly tests from three measurement points within the hydropower plant on the Ślęza River in the city of Wrocław (points upstream and downstream the hydropower plant and the reference point), from the period June 2018 to May 2020. The analyses covered 10 physicochemical parameters, i.e.: pH, electrical conductivity (EC), water temperature, turbidity, NH4-N, NO3-N, NO2-N, total phosphorus, dissolved oxygen and BOD5. The conducted analysis showed that the hydropower plant has no clear influence on the physicochemical quality of the water in the Ślęza River, other interactions present in the catchment area are more important. From the effects visible in the results, a decrease in the amplitudes of water temperature downstream the hydropower plant compared to the other points was noted, as well as a lower median of its value (statistically significant changes). An additional noticeable effect was the increase in water oxygenation below the damming, but it was not statistically significant. It has been shown that the physicochemical condition of water at the tested points does not meet the assumed standards for 8 out of 9 parameters (except for water temperature). The largest exceedances of the limit values concerned NO2-N (up to 923% of the norm), and the most consistent, almost constantly occurring – EC (23 out of 24 months). The reason for the high NO2-N content was most probably surface runoff from the fields and the re-suspension of sediments rich in nutrients, while in the case of EC, its high values result from the specificity of the catchment area.