SELF-PURIFICATION OF THE DNIPROVS’KE RESERVOIR AS A LEADING FORMING FACTOR FOR THE ECOLOGICALLY SAFE HABITAT OF FISHES

Purpose. To study the development of the water quality of the Dniprovs’ke reservoir, which is a water of body of complex including fisheries importance and is characterized by an increased anthropogenic pressure as a result of the processes of the toxification and self-purification determined based on toxicity index (Іt). Methodology. We used the methods of bioindication (determination of the number and biomass of phytoplankton and heterotrophic bacterioplankton), biotesting (Іt determinaiton with the aid of Daphnia magna), hydrochemistry (determination of main trophic-saprobiological parameters of water quality) as well as the correlation analysis of these parameters. Findings. According to the 2012 data, tropho-saprobiologic, algological, microbiological parameters and toxicity index as an integral parameter were analyzed concerning to water quality. Regularities of dynamics and relationship of the indexes were studied. The environmental assessment of water quality of the most polluted upper part of the Dniprovs’ke reservoirs was carried out for each of the parameters studied: in areas where agro-industrial wastes enter, water is classified as ?moderately polluted? ? ?very dirty?. The data testify to strong local water pollution of the reservoir and a good renewable ability of the ecosystem. It was shown that in conditions of human toxification the adequate response concerning water quality gives the toxicity index as an integral indicator of toxification and self-purification processes. The dual role of phytoplankton and heterotrophic bacterioplankton in formation of water quality of the anthropogenically loaded reservoir was revealed: these components are involved in the processes of self-purification or toxification in accordance with periods of microalgae development during the season. This is displayed in corresponding changes of TI and the correlation coefficient. It was found that the self-cleaning of the reservoir is a major factor of improvement of the reservoir water quality and, consequently, the formation of environmentally safe habitat for fish. This is the main regularity, which affects the formation of self-cleaning processes and is reflected through the relations between hydrochemical, toxicological and hydrobiological indexes, the leading role in which is played by phytoplankton ?blooming?. Originality. For the fist time we showed that the correlation coefficient of the parameter with It gives an estimate of the contribution of the corresponding component of the reservoir ecosystem to the result of its toxification and self-purification. Practical value. The relationships, which relate It to ecosystem components, are important for the development of models for water quality and fish-productivity management.