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Microbiological and isotopic-geochemical investigations of the brackish meromictic lakes Shira and Shunet were performed in the steppe region of Khakasia in winter. Measurements made with a submersed sensor demonstrated that one-meter ice transmits light in a quantity sufficient for oxygenic and anoxygenic photosynthesis. As in the summer season, in the community of phototrophic bacteria found in Lake Shira, the purple sulfur bacteria Amoebobacter purpureus dominated, whereas, in Lake Shunet, the green sulfur bacteria Pelodictyon luteolum were predominant. Photosynthetic production, measured using the radioisotopic method, was several times lower than that in summer. The rates of sulfate reduction and production and oxidation of methane in the water column and bottom sediments were also lower than those recorded in summer. The process of anaerobic methane oxidation in the sediments was an exception, being more intense in winter than in summer. The data from radioisotopic measurements of the rates of microbial processes correlate well with the results of determination of the isotopic composition of organic and mineral carbon (delta13C) and hydrogen sulfide and sulfate (delta34S) and suggest considerable seasonal variations in the activity of the microbial community in the water bodies investigated.

The aim of the paper is to investigate accumulation of artificial radionuclides by the Yenisei River aquatic plants collected in the area affected by the activity of the Mining-and-Chemical Combine (Zheleznogorsk) from 1997 to 2000. The samples of aquatic plants were of four species: Potamogeton lucens, Fontinalis antipyretica, Elodea canadensis, and Ceratophyllum demersum. The gamma-spectrometric analysis of the samples of aquatic plants for artificial radionuclides revealed a wide spectrum of long-half-life and short-half-life radionuclides. Radionuclides of activation origin were found in the aquatic plants taken both near the Combine and 200 km down of it. The data obtained suggest that the cooling water of the operating reactor is still being released into the Yenisei. The radiochemical analysis of aquatic plants revealed strontium and plutonium isotopes. Among the aquatic plants, the highest concentration factors for the principal radionuclides were recorded in Fontinalis antipyretica (water moss).