Ecological characteristics of Lake Muy (West Karelia) in conditions of economic development

The presented article considers the complex impact of cage farming of rainbow trout on the ecological state of Lake Mui, located in the Republic of Karelia. For the first time, detailed hydrobiological studies have been conducted, supplementing traditional hydrological and hydrochemical analyses, which allows us to get a more complete picture of the processes occurring in the ecosystem of the reservoir. The results of hydrological monitoring indicate the suitability of Lake Mui for aquaculture purposes, in particular, for trout farming in cages. However, hydrochemical parameters, including the concentration of dissolved oxygen, biogenic elements and suspended solids, indicate that the lake belongs to the mesotrophic type, which implies a moderate content of organic matter and nutrients. The state of the zooplankton community also corresponds to the mesotrophic status of the lake. The saprobity indices characterizing the degree of organic pollution are in the range of 1.72-1.83, which corresponds to the -mesosaprobic zone and the third class of water quality (moderately polluted waters). The analysis of benthic organisms inhabiting the lake bottom revealed signs of the oligo-mesotrophic type according to the trophic scale, according to the saprobity index (2.11) – to the mesosaprobic type, which may indicate the accumulation of organic matter in the bottom sediments. The article emphasizes the need to include hydrobiological studies in the mandatory list when conducting environmental assessments of water bodies used for cage fish farming. Hydrobionts, as the most sensitive components of the ecosystem, quickly respond to any changes, which allows for the timely detection of negative consequences of aquaculture. In conclusion, the authors confirm the advisability of maintaining trout production volumes at the level of 200 tons per year, as recommended earlier. Also, specific timeframes for conducting an environmental assessment of Lake Mui are proposed, which will ensure systematic monitoring of the state of the reservoir and timely adoption of measures for its protection.