Abstract
The purpose of the research is the possibility of using a suspension of Chlorella vulgaris SKO A RKM-0870 strain to improve the hydrochemical and hydrobiological parameters of freshwater reservoirs. The study was conducted in 2022-2023 at the natural reservoir of the Kostanay region with an area of 100 hectares, a depth of 2.5 - 3.0 m. A suspension of chlorella with a density of ≥ 25*106 cells/ml was applied in February, May, June at the rate of 25 l/ha of surface. In 2023, the most significant changes in indicators occurred between May and October. The content of ammonium nitrogen decreased by 3.3 mg/dm3. The amount of dissolved oxygen increased by 9.4 mg/dm3. From May to September 2023, there was a relative increase in the number of chlorella in the group of green algae by 10.05%. The presence of chlorella caused intensive reproduction of filter-feeding zooplankton to 234828 specimens/m3 in July, up to 186670 specimens/m3 in August, and up to 152139 specimens/m3 in September. The maximum number of copepods was observed in August - 124333 specimens/m3 (66.61% of the total number), cladocerans - in July - 186158 specimens/m3 (79.27%), rotifers - in August - 60402 specimens/m3 (39.70 %). Compared to 2022, a sharp boost in biomass and period of active reproduction of zooplankton increased the fodder base of freshwater plankton-feeding fish. This allows rational use of freshwater reservoirs in the northern region of Kazakhstan for the intensive development of fisheries.