The Ecosystem of Lake Tolpanjärvi, Western Karelia, Preserved in the Natural State.

Results of a study of Lake Tolpanjärvi's ecosystem are reported. Its hydrological and geochemical indices, as well as the current condition of biotic communities (the zooplankton, benthos, and fish population), were studied and analyzed. Analysis of the chemical composition of water indicates that the lake has a low organic-matter content (total phosphorus 0.007 mg/L, nitrogen 0.26 mg/L). Lake Tolpanjärvi is an oligotrophic lake, as indicated by the abundance of zooplankton (with a biomass of less than 1 g/m³) and zoobenthos (biomass 0.44 g/m²). The lake is of an oligosaprobic class (second-quality class, clean natural water), as evidenced by its saprobity index estimated using the Pantle–Buck method. The quantitative indices of the zoobenthos varied from 120 individuals/m² and 0.08 g/m² in the profundal zone to 1200 inds./m² and 0.86 g/m² in the quiet littoral zone. The lake is more similar in the chironomid index (K 2.10) to clean natural water. It is inhabited by eight fish species of five families. The fish population is dominated by the whitefish Coregonus lavaretus, the perch Perca fluviatilis, and the roach Rutilus rutilus. Two ecological forms of whitefish, differing in both the number of gill rakers (sparsely rakered 18–24 and medium-rakered 28–36) and biological indices (size–weight, maturation, fertility, and feeding), occur in the lake. Stable highly diverse ecosystems were shown to form the basis for the preservation of the gene pool and for assessment of the current condition of water bodies heavily affected by human activities. [ABSTRACT FROM AUTHOR]