Radionuclide Cycling

By definition radionuclide cycling implies recurrent transfers of radioelements between and within ecosystems of the biosphere. The circulation of elements in ecosystems is an important regulatory process as well as a possible boundary condition for characterizing ecosystems. Because of increased recognition of the importance of cycling there has been a considerable increase in biogeochemical studies of terrestrial environments. That the ecologic processes of biogeochemical cycling govern the movement of and are the determinants affecting long-term behavior of long-lived radionuclides, were not recognized sufficiently to merit serious research attention until the late 1950's. Since then, radionuclide cycling has become a recognized facet of radioecological research. The concept currently appears to include four categories of investigation. They are: (1) deductive analyses derived from studies of fallout nuclides in different trophic levels of varying ecosystems, (2) tracer experiments to elucidate links in a food chain and develop data on rate of movement in the chain, (3) studies of rates of turnover of particular radionuclides within a single trophic level and (4) experiments employing tracers to measure the complete cycle in an ecosystem. Current problems such as interpretation of the significance of 90Sr and 137Cs levels in selected compartments of arctic ecosystems reinforce the need for more experiments of the fourth category emphasizing simple ecosystems.