In August 2021, in the channel part of the Volga River, within the river stretch between Priluki village and Krasnyi Profintern townlet, studies of bacterio- and mycoplankton have been carried out. The study was conducted at 25 stations.The quantitative structure of communities of heterotrophic microorganisms is presented by individual stations and by groups of stations identified by the type of anthropogenic load: “across from a settlement”, “lower border of a settlement”, “5 km downstream from a settlement”, “10 km downstream from a settlement”, “water intake”. The water quality was assessed. Saprophytic bacteria were isolated by the pour-plate method, the total number of bacteria and fungal propagules was determined by direct counting using an epifluorescence microscope. The total number of bacteria at the stations ranged 98.65–99.97% (on average 98.63%) and exceeded the fungi number by 73.0–3824.4 times (on average 1177.8 times). The bacterial biomass amounted to 90.0–99.86% (on average 98.63%) and exceeded the fungal one by 9.0–663.8 times (on average 168 times). In the structure of mycobiota, the mycelium biomass ranged 46.56–96.82% (on average 62.06%), which indicates the functional activity of fungi. Cluster analysis of the quantitative structure of microbial communities, for individual stations, revealed their high similarity: the values of the Bray-Curtis coefficients for number ranged 74.49–99.21%; for biomass – 71.03–98.34%. Cluster analysis of microbial communities by station groups also revealed their significant similarity: in number – 86.6–98.3%; in biomass – 88.20–98.87%. For groups of stations, a high correlation was found between the biomass of bacteria and fungi – –0.85, which indicates different environmental conditions favorable for the development of these microorganisms. The water quality in the station groups was appraised as transitional from polluted to dirty waters, from β-mesosaprobic to polysaprobic, and in trophicity, from mesotrophic to eutrophic.
bacterioplankton, mycoplankton, number and biomass of microorganisms, saprophytic bacteria, water quality
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