Cs-137 and Pb-210 in lacustrine sediments of Stepnoi Altai as indicators of the dynamics of anthropogene changes in geochemical background throughoutthe 20th century

Three of tens of small lakes in Stepnoi Altai were studied in detail. In on e of them, located in the center of the region, far from the sources of tec hnogenic components, bottom sediments from a 25 cm deep column were sampled , with a sampling step of 1.5 cm. For all samples, a gamma spectrometric an alysis of the activities of Cs-137 and Pb-210 and atomic-absorption analysi s for heavy metals (Cu, Zn, Ni, Co, Pb, Cd, Hg), As, and Be were performed. It has been established that the wind erosion of soils of the surrounding watersheds affected the chemical composition of forming lacustrine sediment s. The activities of Cs-137 and Pb-210 in the sediments are two or three ti mes higher than those in atmospheric precipitation, which also evidences th at soils are "intermediate collectors" of technogenic radionuclides. The la tter were probably transported mainly by sand storms, which are typical of Stepnoi Altai. From the Pb-210 distribution throughout the column, we have estimated the dynamics of changes in concentrations of Al, Fe, organic matt er, heavy metals, As, and Be in the sediments. The greatest compositional c hanges of the sediments were caused by the disruption of the natural soil c over during the exploration of virgin and long-fallow lands, which provoked intense sand storms. Despite the slight increase in concentrations of heav y metals for the last 100 years, they virtually do not exceed their clarkes for sedimentary rocks. Therefore, the central part of Stepnoi Altai may be considered unpolluted by technogenic components.