Formulation of the problem. Global climate change causes transformation in the humidification regime and, as a result, makes adjustments to economic activities and features of water use. In the context of Ukraine, against the background of climate change, the runoff of most domestic rivers is declining, which especially in the limited period exacerbates the issue of balanced use of ecosystem services of aquatic ecosystems and prioritization of needs during resource allocation, control of rivers and establishment of their functioning.
The purpose of the article. Recognizing the strategic importance of freshwater ecosystems in ensuring sustainable regional and national development, the study of the Southern Bug River was aimed at assessing its ecological status in order to identify sources of negative anthropogenic impact and identify general ecosystem distortions that may affect the functional integrity of the aquatic ecosystem.
Methods. The research points on the Southern Bug River were determined by the method of randomization. The total length of the route was about 200 km. Also, the spatial location of settlements was taken into account, so that the investigated points were both upstream and downstream. Measurement of physicochemical parameters was performed by instruments: TDS-3, TDS/ЕС/Temp-meter HM COM-100, pH-meter Ezodo 6011A. The task of hydrobiological research was to find and identify species at the family level. The research was conducted at the end of July 2020, when the river entered to low flow phase.
Results. On the basis of field research, the assessment of the ecological state of the Southern Bug River in the lower course (from the city of Pivdennoukrainsk) was carried out in the work. Regularities of pH dynamics and mineralization of the aquatic environment are established. The limits of the spatial influence of the Black Sea waters on the Southern Bug, the continental advance of which (upstream) almost 100 km up is due to the high level of regulation of basin runoff, have been specified. The same processes, as a consequence, affect not only biodiversity, but also the features of industrial and domestic water use. Using the stenobiontic approach, the level of ecological safety of the Southern Bug ecosystem in the lower course was assessed. Based on the obtained results of stenobioindication, the zoning of the studied area of the Southern Bug is proposed, which compares quite well with the results of pH and mineralization measurements. Only 1% of the route, which corresponds to the porous section of the river channel, was classified as a "healthy ecosystem". The closer to the mouth, the pH of the water gradually increases, which contributes to the intensification of the eutrophication process.
Scientific novelty and practical significance. The obtained results are considered to be an integral part of future field research on the identification of sources of negative impact on the aquatic ecosystem of the Southern Bug.
The novelty of the results obtained is a comprehensive assessment of the ecological state of the river ecosystem in the low flow period, which, in contrast to the concept of maximum permissible concentration, characterizes the state of the Southern Bug not point, but takes into account the cumulative and synergistic effects of anthropogenic impact. The latter are best manifested during the summer season, as a result of which the structure and biomass of the river's food chain change significantly.
In addition, the analysis of the rational use of water resources of rivers allowed us to state that the modern system of environmental standards, which in particular regulate the quality of the aquatic environment, cannot ensure the preservation of river ecosystems.
Anthropogenic impact on the ecological state of Kamensk-Uralsky