Coastal Water Quality in Lake Baikal in Bol’shie Koty Bay, Determined by the Effect of Atmospheric Precipitation and the Survival of Indicator Microorganisms

Sanitary-bacteriological and hydrochemical study of coastal water of Lake Baikal, including bottom and interstitial water, was carried out near Bol’shie Koty Settl. in June and September 2022. The study involved methods of classical sanitary microbiology with the use of methods of vacuum filtration and selective media for germination of sanitary indicative microorganisms. The concentrations of chemical components were determined by methods of high-performance liquid chromatography and spectrophotometry. The quality of water in recreation zones, as well as within the boundaries of populated areas used for bathing in the coastal zone of the settlement was found to meet the criteria of regulatory and technical documentation adopted in Russia in terms of indicators Escherichia coli and enterococci. The concentrations of hydrochemical components, such as phosphate phosphorus (P- \({\text{PO}}_{4}^{{3 - }}\) ); ammonium (N- \({\text{NH}}_{4}^{ + }\) ), nitrate (N- \({\text{NO}}_{3}^{ - }\) ) and nitrite (N- \({\text{NO}}_{2}^{ - }\) ) nitrogen, also did not exceed the values of MAC established in Russia for water bodies used for fishery. The survival rate of E. coli and enterococci was studied in Baikal water and in the interstitial water, which is of importance for the choice of indicators to assess coastal water quality. In the course of the study, it was determined that E. coli and enterococci remained physiologically active longer in interstitial than in coastal water. It was found that the concentrations of fecal indicator bacteria in the coastal zone of the lake can increase depending on the amount of precipitation due to the washing-off of microorganisms from the shore. The study of the effect of nutrients in atmospheric precipitation on the coastal water showed that rains had no effect on the amount of nutrients in the examined surface and bottom water.