Use of natural and artificial radionuclides to determine the sedimentation rates in two North Caucasus lakes

The specific activities of natural (210Pb, 226Ra, and 232Th) and artificial (137Cs, 239,240Pu, and 241Am) radionuclides in the sediments of two North Caucasus lakes were determined. The two lakes, Lake Khuko and Lake Donguz-Orun, differ in their sedimentation conditions. Based on the use of unsupported 210Pbex and both Chernobyl-derived and bomb-derived 137Cs as chronological markers, it was established that the sedimentation rates in Lake Khuko over the past 55–60 y did not exceed 0.017 cm y−1. Sedimentation rates in Lake Donguz-Orun were found to be more than an order of magnitude higher. In the latter case, the sedimentation rates for the period from 1986 to the present were over 1.5 times higher than they were for the period 1963–1986. The differences in sedimentation rates were due to differences in the rates of denudation of their respective catchment areas. The specific activities of artificial radionuclides (137Cs, 2600 Bq kg−1; 239,240Pu, 162 Bq kg−1; and 241Am, 36 Bq kg−1) and their ratios in the sediments of Lake Khuko show that their deposition was mainly due to global stratospheric fallout of technogenic radionuclides associated with nuclear bomb testing during 1954–1963—rather than fallout from the Chernobyl accident. Several factors, including the mode of precipitation, features of the surface runoff, and location of Lake Khuko, were responsible for the accumulation of artificial radionuclides. [Display omitted] •Both 137Cs and 210Pbex were used for evaluation of sedimentation rates in the two Caucasus lakes.•Sedimentation rate in Donguz-Orun lake located in proglacial zone increase in 1,5 times since 1986.•Global warming is the main reason of increasing denudation rates in periglacial zone.•High concentrations of technogenic radionuclides were determined in sediments of Lake Khuko.•The possible contribution of different sources of Khuko lake sediment contamination is determined. Main finding: It was determined that global warming is the primary reason the denudation rates in the periglacial zone are increasing. The possible sources of the radioactive contamination of the Khuko lake sediment were also determined.