Simulation of radionuclide fluxes from the Dnieper-Bug Estuary into the Black Sea

To simulate the radionuclide flux from the Dnieper–Bug Estuary into the Black Sea the three-dimensional time-dependent flow and transport code THREETOX was used. The prognostic variables of the model are the three components of the velocity field, temperature, salinity, surface elevation, suspended sediment concentration and the radionuclide concentrations in the solute, suspended sediments and bottom deposition. The dispersion of 137Cs and 90Sr in the estuary and adjacent shelf area of the Black Sea over the first two years following the Chernobyl accident was reconstructed. The fluxes of radionuclides from the Dnieper–Bug Estuary into the Black Sea were estimated. The results are in reasonable agreement with the available measurements. It is shown that the differences between the 137Cs and 90Sr distributions specific to the Dnieper–Bug Estuary were due to the different geochemical behaviours of these radionuclides. The deviation from a linear correlation between salinity and dissolved 137Cs concentration in the estuary was shown to be due to exchange processes with contaminated bottom sediments.