The objectives of the article are: to assess spatio-temporal evolution of eutrophication and water quality of the Turawa dam reservoir, located in south-western Poland on the Mała Panew River; to identify location and relationship between potential sources of physicochemical pollution related to the progressing process of eutrophication; and to determine trophic status and water quality indices of the selected research object. The analysis (Mann–Whitney U test, PCA, HCA, Spearman correlation matrix) showed a high susceptibility of the reservoir to eutrophication processes, especially due to the influence of dangerous loads of compounds emerging from areas with high tourist intensity and pollutants flowing from the Mała Panew River. The parameters deteriorating the ecological status were TP, DO, BOD5, and COD. Considering the cumulative results of water quality indices for the period 1998–2020, the average water quality was in classes II or III. A noticeable deterioration appeared in water quality for the years 2016–2020, which proves the progressing eutrophication in the Turawa reservoir. In 1998–2020, the reservoir was classified as eutrophic or mesoeutrophic based on the calculated three trophic status indices. This article would help in developing a strategy for dealing with water blooms, a reliable system for monitoring pressures causing eutrophication, and optimal technologies for the reconstruction of multifunctional reservoirs.

Hydropower plants affect the distribution and composition of sediments. The main aim of this study was to analyze the spatial distribution of sediment pollution in the vicinity of a small hydropower plant. The grain composition of the sediments, the content of heavy metals (Cu, Ni, Cr, Zn, Pb, and Cd) and select physicochemical properties (pH, electrolytic conductivity) were tested at 14 points upstream and downstream of the hydropower plant on the Ślęza River in Poland, as well as at reference point. The interactions between the tested parameters were also verified. The results of the conducted analysis show that hydropower plants significantly affect the composition and properties of sediments. Large amounts of sediment are deposited on damming weirs, accumulating heavy metals and other substances. The differences in the concentrations of elements were significant, and Cu, Ni, Cr, Zn and Pb were 8.74, 9.53, 3.63, 8.26 and 6.33 times higher, respectively, than the median value at points upstream of the hydropower plant than downstream. It was shown that the tested parameters of the sediments interact with each other and are correlated; heavy metals showed a synergistic effect, while other parameters configurations showed an antagonistic effect. The higher content of heavy metals upstream of the hydropower plant resulted from the presence of finer sediment—classified as silt—in this section. Downstream of the hydropower plant, there were mainly sands, which showed a lower ability to absorb substances. This work contributes to improving the rational management of the worldwide issue of sediments within dams located in river valleys. Moreover, it is in line with the 2030 Sustainable Development Goals adopted by the United Nations, particularly in the fields of clean water and sanitation, clean and available energy, and responsible consumption and production.

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The installation improving water quality (IIWQ) was installed on the Turawa dam reservoir (50º43'25 "N 18º07'13" E) on the Mała Panew river in the Opolskie Voivodeship (south-western Poland). The Turawa water reservoir is a multifunctional reservoir with an 80-year service life, built for the purpose of water retention for the maintenance of the Odra River flows for navigation, recreation and rest, and for energy purposes. The area where the Turawa reservoir is located is rich in nature. There are valuable natural areas, legally protected -Natura 2000 area Turawa Reservoir, created in 2008 to protect birds and their habitats, as well as the protected landscape area "Lasy Stobrawsko-Turawskie". The studies of the water quality of the Mała Panew River and the Turawa reservoir conducted in 1998-2009 and 2011-2016 indicate that the Turawa reservoir had an impact on the improvement of the water quality of the Mała Panew river.The purpose of the IIWQ is to improve the water quality in the reservoir in the designated area of the Turawa reservoir at the WOPR marina. The research period covered measurements from June 2019 to May 2020, while from May 2020 to December 2021, the effectiveness of the operating installation was tested in the context of reducing the concentration of nitrates and phosphates. The paper presents the results of water quality tests in the Turawa reservoir in the first period of operation of the installation, in terms of selected parameters at selected measuring points within IIWQ. Based on the information on the volume of nutrient loads flowing in and out of the installation, the impact of the installation on the improvement of water quality in the reservoir was determined. In addition, control tests were carried out at checkpoints in the reservoir. It has been shown that the causes of water blooms in this area are municipal springs as well as agriculture (surface runoff of fertilizers and pesticides from the fields). Eutrophication also has a serious impact on the functioning of organisms living in the water, as well as on the health of people using the reservoir (the algae causing eutrophication are toxic).This research was carried out as part of the National Center for Research and Development BIOSTRATEG3/343733/15/NCBR/2018 project entitled "An innovative method of improving water quality in multifunctional retention reservoirs".

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The purpose of water reservoirs has changed over the years. In times of intensified anthropopressure processes, dam reservoirs lose their original meaning only as an ecosystem that is a place of life for various aquatic organisms. Eutrophication also has a serious impact on the functioning of organisms living in the water, as well as on the health of people using the reservoir (the algae causing eutrophication are toxic).The installation improving the quality (IIWQ) of water "Ventura" is located on the Turawa reservoir (50º43'25 "N 18º07'13" E), located in 18,900 km of the Mała Panew river in the Opolskie Voivodeship in Poland. The Ventura facility is located on the right bank of the Turawa reservoir, the area of operation of the installation includes the reservoir bay, where the adjacent area is used for tourism as a camping site. Due to the characteristics of the area, we observe large changes in nitrogen concentration during the study period. The Turawa reservoir was built in the years 1933-1939 for the purpose of water retention for the maintenance of the Odra flows for navigation purposes, and for recreation and relaxation. The tourist potential and the landscape and natural value of the site are drastically reduced during the growing season due to excessive eutrophication. Large amounts of nitrogen and phosphorus loads flowing into the waters of the Turawa reservoir significantly contribute to the gradual eutrophication, deteriorating the living conditions of aquatic organisms and limiting the possibilities of using the accumulated waters.The aim of the work was to compare the water quality status before the installation is put into operation, during its operation and after the end of the 3-year period of operation. The paper presents the results of water quality tests. Based on the information on the volume of nutrient loads flowing in and out of the installation, the impact of the installation on the improvement of water quality in the reservoir was determined. In addition, control tests were carried out at checkpoints in the reservoir. It was found that increased eutrophication processes occur in the Turawa reservoir, which is mainly determined by nitrogen compounds. The research period covered measurements from June 2019 to May 2020, while from May 2020 to December 2021, the effectiveness of the operating installation was tested in the context of reducing the concentration of nitrates and phosphates.