PHYTOPLANKTON OF THE DUBOVETS RIVER (DNIPRO BASIN) AS AN INDICATOR OF THE STATE OF THE WATER ECOSYSTEM OF A SMALL RESERVOIR

Abstract

The paper discusses the results of phytoplankton research in the Teterev tributary, the Dubovets River, obtained during expeditionary studies in 2025 (April, July, and October). In total, 94 species of algae were found in the river phytoplankton, represented by 104 intraspecific taxa with a nomenclatural species type, including 7 divisions: Chlorophyta − 37 видів (40 в.в.т.), Bacillariophyta − 28 (31), Euglenozoa − 11 (13), Cyanobacteria − 9 (10), Ochrophyta − 5 (6), Miozoa and Cryptophyta − по 2 (2) each. Green and diatom algae were the structure-forming divisions in all seasons, with diatom, green, and euglenoid algae having the highest frequency of occurrence. The highest saturation of genera with species and intraspecific taxa was found in the Euglenozoa and Ochrophyta divisions, indicating the highest adaptive potential of these groups of algae at the current stage of river ecosystem functioning. The average value of phytoplankton biomass in the Dubovets River was 2.65 ± 0.12 mg/dm3, and the abundance was 5.54 ± 2.59 million cells/dm3. Therefore, based on phytoplankton biomass, the water quality belongs to class III, “polluted,” category “slightly polluted.” However, an increase in biomass was observed in the summer period (4.38 ± 0.99 mg/dm3), mainly due to the intensive vegetation of blue-green algae (their share in the biomass structure in summer was 51%, and their abundance was 92%). During this period, a decrease in the Shannon index was also observed, and thus a transition from a polydominant phytoplankton structure during spring and autumn to an oligodominant one in summer. The ability of the autotrophic link of the river ecosystem to self-regenerate is indicated by a significant proportion of dominant species in the dominant complex, which, having a high production potential, determine the compensatory mechanism for maintaining a stable balance of organic matter. Plankton-benthic forms played a leading role in the phytoplankton structure of the Dubovets River. In terms of geographical distribution, the river’s algal plankton is heterogeneous, but its floristic composition is dominated by cosmopolitan species. In terms of pH, algae are mostly indifferent and alkaliphilic; in terms of halophility, they are indifferent and halophytic; in terms of rheophility, they are indifferent; in terms of temperature preference, they are eurythermic. β-mesosaprobic species predominate in the phytoplankton of the watercourse, and the saprobity index, calculated based on phytoplankton biomass, reached 1.9±0.06 (water quality class “clean,” category “fairly clean”).