Today, 33 years after the Chernobyl accident, long-term dynamics of radio-cesium in the environment becomes the most relevant issue. Study of bottom sediments in lakes and reservoirs provide insight in understanding long-term dynamics of radionuclides strongly bound to sediment particles such as 137Cs. With this in mind, in 2018 a number of cores of bottom sediments were collected in the deep parts of Lake Glubokoe, Lake Azbuchin and Cooling Pond in the close vicinity of the Chernobyl NPP and in Schekino reservoir (Upa River) in Tula region of Russia. All these water bodies were contaminated as a result of the accident in 1986. The collected bottom sediment cores were sliced in 2-cm layers, dried and passed through 2-mm sieve, after which analyzed for 137Cs using γ-spectrometry. The obtained 137Cs vertical distributions in sediments accumulation zones of the water bodies suggest that almost no vertical mixing of sediments has occurred, and the 137Cs peaks are well-defined and not diffuse ones. Assuming that sediment accumulation rates after the accident were more or less uniform, layers of bottom sediments can be attributed to certain time of sedimentation. With 137Cs activity concentration in a given layer of bottom sediments corresponding to 137Cs concentration on suspended matter at that point in time, we were able to obtain the dynamics of particulate 137Cs activity concentrations from 1986 to 2018. Using the experimental values of the distribution coefficient Kd, changes in the dissolved 137Cs activity concentrations in the above water bodies have been estimated for the period of 32 years after the accident. The estimates of dissolved 137Cs concentrations seem to be in reasonable agreement with monitoring data. By and large, the general trend of the particulate and dissolved 137Cs and 241Am activity concentrations in all water bodies are consistent with the semi-empirical “diffusional” model. This research was supported by Science and Technology Research Partnership for Sustainable Development (SATREPS), Japan Science and Technology Agency (JST)/Japan International Cooperation Agency (JICA) (JPMJSA 1603) and by bilateral project No. 18-55-50002 of Russian Foundation for Basic Research (RFBR) and Japan Society for the Promotion of Science (JSPS).

Quantifying and understanding catchment sediment yields is crucial both from a scientific and environmental management perspective. To deepen the understanding of land use impacts and climate change on sediment load, we explore mechanisms of the suspended sediment yield formation in the Northern Caucasus during the Anthropocene. We examine how sediment flux of various river basins with different land-use/landcover and glacier cover changes during the 1925-2018 period. Our analysis is based on observed mean annual suspended sediment discharges (SSD, kg·s−1) and annual fluxes (SSL, t·yr−1) from 33 Roshydromet gauging stations (Russia). SSL series have been analyzed to detect statistically significant changes during the 1925-2018 period. The occurrence of abrupt change points in SSD was investigated using cumulative sum (CUSUM) charts. We found that SSL has decreased by −1.81% per year on average at most gauges. However, the decline was not linear. Several transition years are expected in the region: increasing trends from the 1950s and decreasing trends from 1988-1994. Correlation analyses showed that variation in SSL trend values is mainly explained by gauging station altitude, differences in land use (i.e., the fraction of cropland), and catchment area. Nonetheless, more accurate quantifications of SSL trend values and more refined characterizations of the catchments regarding (historical) land use, soil types/lithology, weather conditions, and topography may reveal other tendencies.