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The paper reports the results of the analysis of Pb, Sb, Cd accumulation in top core sediments from small lakes of southern Republic of Karelia. Both lakes in urban areas (Petrozavodsk, Medvezhyegorsk, Suojarvi, and Sortavala) and lakes in areas regarded as reference for southern Karelia were included in the study. Fieldwork and analytical investigations employed a common methodology in line with globally-accepted limnological practices. The concentrations of chemical elements in the lake sediments were determined by inductively coupled plasma mass spectrometry (ICP-MS). The median background concentrations of Pb, Sb, Cd in the studied sediments deposited in the preindustrial period were calculated, and the recent levels of accumulation of these metals in the industrial period were determined for the same lakes. The main factors for the formation of technogenic Pb, Sb, Cd anomalies in the top core sediments are described, and the levels of the heavy metals are compared against those in lake sediments in other parts of the world. The levels of contamination of the Karelian lakes with these metals were calculated based on the geoaccumulation index Igeo. The Tessier sequential extraction procedure was employed to detect the main forms of the heavy metals in the top core sediments. Especially, the role of organic matter, which constitutes the bulk of the sediments, in binding the pollutants was assessed. Considering that Karelian lake sediments are potential sources of useful organic raw material, i.e. sapropel, some recommendations are given on the possible applications of these sediments in human activities.

Complex ecological studies of five small lakes under direct impact of the Monchegorsk site of JSC «Kolskaya GMK» have been conducted. The lakes ecosystems develop under extreme pollution, and characterized by depleted species composition of hydrobionts and low values of their abundance and biomass. Lake Kumuzhye, with the least transformed watershed, is closest to natural environment. Lake Nyudyavr, affecting by cuprum-nikel production sewages is additionally susceptible to anthropogenic eutrophication, which obviously contributes in part to the resistance of hydrobionts to toxic load. It is established that the use of traditional hydrobiological criteria for assessment of water quality and trophic status for the studied water bodies is limited.

The paper summarizes the results of integrated study of current state of freshwater biota of small water bodies, located in the area of ‘Fedorova tundra’ intrusion. A list of species composition is given, quantitative and structural indicators of phytoplankton, zooplankton, zoobenthos and fish are assessed. Size-weight, age and sex structure of dominant ichthyofauna are estimated. The obtained results can be used as the reference values for further monitoring of the ecological status of the water bodies.