Current state of bacterioplankton of Lake Ilmen

Objective : Determination of the quantitative level of the Lake Ilmen bacterial community in a retrospective. Assessment of lake water quality by microbiological indicators based on the results of seasonal microbiological studies in 2022 Research material and methods used : The material was samples of bacterioplankton from the surface water layer of the Lake Ilmen, collected in May, August and September 2022. The total numbers of microorganisms was determined by the epifluorescence method using DAPI fluorochrome. Standard methods were used to determine the number of saprophytic microorganisms at two temperature regimes. Originality: For the first time in the last 25 years, the quantitative characteristics of the bacterial community of Lake Ilmen were determined. A quality assessment of lake waters has been carried out, and the values of self-purification coefficients were calculated. Results : The microbiological characteristic of the water masses of Lake Ilmen, as a habitat for bioresources, is presented. The maximum values of the total bacterial numbers (TBN) were observed in May (average 5.05±0.52×106 cells/ml) during the spring flood, the minimum — at the end of September (average 3.21±0.89×106 cells/ml) during the cooling period of the lake. Coccoid cells prevailed in the bacterioplankton, which indirectly indicates the absence of contamination of the lake waters with organic matter of various origins. According to the average for the observation period TBN (4.10±1.05×106 cells/ml), the trophic state of the lake corresponded to weakly eutrophic. The number of saprophytic bacteria growing at 22 °С always exceeded that at 37oC, which indicated active self-purification processes. According to the quantitative ratios of the TBN and the number of saprophytic bacteria growing at 22 °С (OMH 22 °С), the water masses of the lake, with rare exceptions, belonged to the conditional category of “pure” (oligosaprobic)