Bacterioplankton and Bacteriobenthos as Ecological Indicators of the Reservoirs' Ecology-Sanitary State and the Safety of Water Use

Abstract

Bacterioplankton and bacteriobenthos of the middle and lower sections of the Kyiv Reservoir, and the upper section of the Kaniv Reservoir was studied in July 2021 under abnormally high water and air temperatures. The average numbers of bacterioplankton were similarly high (Kyiv Reservoir 14.4 ± 6.2·10<sup>6</sup> cells/cm<sup>3</sup>, Kaniv Reservoir - 17.6 ± 1.4·10<sup>6</sup> cells/cm<sup>3</sup>), with wider range in the Kyiv Reservoir. The bacteriobenthos numbers was significantly higher in the upper section of the Kaniv Reservoir (Kyiv Reservoir - 8.8 ± 5.6·10<sup>9</sup> cells/g, Kaniv Reservoir - 26.5 ± 6.2·10<sup>9</sup> cells/g). Significant differences were found in numbers of different trophic groups: eutrophic and oligotrophic bacteria were more numerous in the Kaniv Reservoir; their ratio (EB/OB) was <1 in the Kyiv Reservoir and >1 in the Kaniv Reservoir. This indirectly indicates the predominance of easily oxidizable organic matter in the upper section of the Kaniv Reservoir under the point pollution of the section within the boundaries of the big city (Kyiv). The significant positive correlation (<i>p</i><0.01) was established between the eutrophic bacteria number in plankton and benthos and organic matters content (in terms of PO). According to the ecological classification of the surface waters' quality based on the of planktonic eutrophic bacteria numbers, the middle section of the Kyiv Reservoir belonged to the categories "very good" - "satisfactory", II, III quality classes, in the near-dam section - "bad" to "poor", IV and V quality classes. The considered sections of the Kaniv Reservoir corresponded to the "poor" category, class V. The content of the opportunistic microflora was maximal in the lower section of the Kyiv Reservoir (the main components were <i>Escherichia coli & coliform</i> and <i>Staphylococcus</i> spp.) and in the Obolon Bay of the Kaniv Reservoir (<i>Enterococcus</i> spp.).