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).

Populations experiencing varying levels of ionising radiation provide an excellent opportunity to study the fundamental drivers of evolution. Radiation can cause mutations, and thus supply genetic variation; it can also select against individuals that are unable to cope with the physiological stresses associated with radiation exposure. Since the nuclear power plant explosion in 1986, the Chernobyl area has experienced a spatially heterogeneous exposure to varying levels of ionising radiation. We sampled Daphnia pulex (a freshwater crustacean) from lakes across the Chernobyl area, genotyped them at ten microsatellite loci, and also calculated the current radiation dose rates. We then investigated whether the pattern of genetic diversity was shaped primarily by radiation-mediated supply of variation consistent with increased supply of de novo mutations, or by radiation-mediated selection and loss of variation at higher dose rates. We found that measures of genetic diversity, including expected heterozygosity and mean allelic richness (an unbiased indicator of diversity) were significantly higher in lakes that experienced higher radiation dose rates; this is consistent with mutation outweighing selection as the key evolutionary force in populations experiencing high radiation dose rates. We also found significant but weak population structure, and clear evidence for isolation by distance between populations. This evidence suggests that gene flow between nearby populations is eroding population structure, and that mutational input in high radiation lakes could, ultimately, supply genetic variation to lower radiation sites.

Changes in the catchment scale water balance have important social implications for usable water now and in the future. Stream discharge is also directly related to radionuclides flux in the river water system. The aim of this study was to clarify the water balance in the Chernobyl Exclusion Zone (CEZ) under current and future climate conditions. A catchment scale hydrological model was used with long-term discharge data to project the future trend of radionuclides wash-off from the contaminated catchment at the CEZ in Ukraine. The Sakhan river catchment at the CEZ (51.41°N, 30.00°E) in Ukraine is one of the Pripyat river systems, and has a total surface area of 186.9 km2. We found that under the current climate, 84% of annual input (sum of rainfall and snowmelt) was consumed as evapotranspiration, and discharge was estimated to be 16%. In future climates, annual precipitation is expected to increase. However, a projected increase in the vapor pressure deficit led the consumption of precipitation as evapotranspiration and no significant increase in discharge. The study found that warmer winter and spring temperatures will decrease the snowfall, and increase the rainfall, but it was not enough to increase evapotranspiration. As a result, the peak of discharge shifted from April to March. The increase of future average discharge during the winter and spring came from a combination of (1) increasing rainfall in the winter and spring, and (2) relatively small levels of evapotranspiration, which enhanced the catchment scale water recharge in soil moisture and gave rise to greater discharge during winter and spring. The reduction of extreme river discharge from the hydrological projections could reduce the probability of high radionuclides concentration in the river water system in the future, owing to the reduction of surface runoff water from the contaminated surface soil and/or top layer of floodplain soils in the CEZ.