The Radionuclides in Lake Ecosystems Within The Chernobyl Accident Exclusion Zone: Ten Years of Researches

During 1997-2007 we studied distribution and dynamics of main radionuclides and their biological significance in lake ecosystems within the 10-km inner exclusion zone around the destroyed unit of the Chernobyl nuclear power plant. The main objects of our studies were bottom sediments, water, seston, and different species of hydrobionts from Azbuchin Lake, Dalekoye-1 Lake and Glubokoye Lake. Selfpurification of lakes within the Chernobyl accident exclusion zone is extremely slow process. Therefore, ecosystems of the majority of lakes, dead channels and crawls possess high level of radionuclide contamination of all the components. About 98-99% of 137Cs and 99% of transuranic elements (238Pu, 239Pu, 240Pu and 241Am) of the total radionuclide content in lake ecosystems has concentrated in the bottom sediments. The part of 90Sr in sediments, due to higher solubility, amounts to 89-95%. About 210% of radionuclides is concentrated in water and only about 1% in biota. In this 1% a prevailing value for different radionuclides has the bivalve molluscs and the higher aquatic plants. The construction of a complex of flood retarding dams, to prevent the radionuclide washout from the left-bank flood plain of the Pripyat River, implied a change of hydrological regime in these territories. The absence of flow in water bodies, stagnation effects during spring flooding and seasonal runoffs intensified waterlogging and swamping of dam-fenced area. As a result, at the background of general growth of 90Sr mobile forms in the soils of water catchment areas within the exclusion zone, there is an expressed tendency to increase of 90Sr content in water and its bioavailability in lakes located at dam-fenced sites. The long-term impact of irradiation on hydrobionts in lakes within the exclusion zone we registered high level of chromosome damages in cells of root meristems of higher aquatic plants and molluscs' embryos.