Reconstruction of the Long-Term Dynamics of Particulate Concentrations and Solid-Liquid Distribution of Radiocesium in Three Severely Contaminated Water Bodies of the Chernobyl Exclusion Zone Based on Current Depth Distribution in Bottom Sediments

Given the importance of understanding long-term dynamics of radionuclides in the environment in general, and major gaps in the knowledge of Cs-137 particulate forms in Chernobyl exclusion zone water bodies, three heavily contaminated water bodies (Lakes Glubokoe, Azbuchin, and Chernobyl NPP Cooling Pond) were studied to reconstruct time changes in particulate concentrations of Cs-137 and its apparent distribution coefficient K-d, based on Cs-137 depth distributions in bottom sediments. Bottom sediment cores collected from deep-water sites of the above water bodies were sliced into 2 cm layers to obtain Cs-137 vertical profile. Assuming negligible sediment mixing and allowing for Cs-137 strong binding to sediment, each layer of the core was attributed to a specific year of profile formation. Using this method, temporal trends for particulate Cs-137 concentrations in the studied water bodies were derived for the first time and they were generally consistent with the semiempirical diffusional model. Based on the back-calculated particulate Cs-137 concentrations, and the available long-term monitoring data for dissolved Cs-137, the dynamics of Cs-137 solid-liquid distribution were reconstructed. Importantly, just a single sediment core collected from a lake or pond many years after a nuclear accident seems to be sufficient to retrieve long-term dynamics of contamination.