—A quantitative assessment of the fractionation of elements during sedimentation is made based on long-term comprehensive studies with the participation of geochemists, hydrobiologists, soil scientists, and chemists. Analytical studies of the chemical composition of water, soil, bottom sediments, and biota were carried out at the Center for Collective Use of Scientific Equipment for Multielement and Isotope Studies and at the Institute of Catalysis, Novosibirsk. Based on a mineralogical and geochemical approach, we chose lakes with different types of biogenetic formation and different classes of organomineral sediments and performed detailed studies of the relationship between the organic and mineral parts of the sediments. It has been established that the organomineral sediments of different classes and biogenetic types of formation differ not only in the contents of major elements (Si, Ca, C, and O) but also in the group composition of organic matter. The direct effect of the transformation of organic matter on the mineral composition of bottom sediments has been revealed. The contents of other elements vary in a narrow range of values. At the same time, the difference in the contents of elements between organomineral sediments of different types and classes is comparable with their difference within a class. The leading role in the formation of the geochemical and mineral compositions of the organomineral sediments of small lakes belongs to intricate biological, biochemical, and physicochemical processes depending mainly on azonal factors and occurring under prolonged freezing-up (anaerobic conditions).

The processes of the migration and concentration of trace elements during sedimentation in small continental lakes in various landscape zones of the south of Western Siberia have been studied. We provide a quantitative assessment of the concentration levels and changes in the regional geochemical background of Cd, Hg, Sb, Zn, and Pb in sapropel deposits over the past 200 years. It was shown that complex natural processes determined by a combination of azonal factors play a fundamental role in the formation of the geochemical and mineral compositions of the bottom sediments of small lakes in various landscape zones in the south of Western Siberia. These consist of: the formation of sedimentary material in the lake catchment depending on the relief, geology, soil, and vegetation cover, as well as anthropogenic influences; the formation of authigenic organic and mineral matter as a result of biological, biochemical, and physicochemical processes; and the deposition of a complex mixture of allochthonous and autochthonous matter at the bottom of a lake, which flows under conditions of prolonged ice formation (anaerobic conditions).

Isotopic variations of carbon of the carbonates and organic matter in bottom sediments of lakes of two lake systems located in the South of Siberia are studied: Baraba (Baraba steppes) and Tazheran (Tazheran steppes). Isotopic studies of δ13C carbonates and organic matter of the lacustrine bottom sediments of the Tazheran and Baraba systems indicate two main mechanisms of authigenic carbonates formation: chemogenic deposition and biochemogenic deposition due to bacterial destruction of organic matter. The dependence of the δ13Corg and δ13Ccarb, the degree of water salinity is not revealed. Forms by chemogenic carbonates are similar to water isotopic values, i.e. with dissolved bicarbonate - ion reservoir. However, in most of the studied lakes the light isotopic composition δ13Ccarb was revealed, as carbonates are formed in the environment with a high content of isotope-light CO2 formed by the oxidation of carbon dioxide emitted by bacteria-decomposers in the mineralization process of the original organic matter in the stagnant waters in the anaerobic environment.

––We studied the bottom sediments of lake systems located in the taiga landscape of Siberia. In the south of Western Siberia, there are 11 lakes in the subzone of the south taiga and 9 lakes in the subtaiga subzone. On the territory of the south of Eastern Siberia in the taiga zone there are 10 lakes on the southern coast of Lake Baikal, 5 lakes on its east coast and 6 lakes are located on the territory of the national park “Alkhanai” in Transbaikalia. Studies of the chemical composition of water, soil, and sediment samples were conducted at the Analytical Center for Multi-Elemental and Isotope Research SB RAS, Novosibirsk. The use of a complex of modern analytical methods in the study of the same lake samples made it possible to obtain more reliable information (1861 samples of bottom sediment were studied). Quartz and feldspars of pelitic dimension dominate in the mineral composition of the terrigenous fraction, organic matter and authigenic minerals (opal, pyrite, illite and sometimes calcite) are added to them during the bottom sediments formation. The absolute contents of the studied elements in the bottom sediments of all lakes are lower than their concentrations in the upper continental crust and sedimentary rocks of the Russian Plate, with the exception of Si, Hg, Cd. In the lakes of the subtaiga of the south of Western Siberia, an exception was established for Ca in the bottom sediments of which carbonates predominate. Contents variations of a number of elements in the bottom sediments of taiga lakes in different regions do not significantly differ. The dispersion of their concentrations between lakes with a total catchment area and lakes from different regions are comparable (Ca, Sr, Al, Mn, Fe, Cd, Hg, etc.). The current sedimentation rate in natural occurrence in the lakes of the taiga zone (southern Siberia) vary from 1.1 to 2.9 mm/year. Moreover, it is comparable to the current sedimentation rate in the lakes of the forest-steppe and steppe zones of south of Western Siberia.