Biogeochemical cycles of Chernobyl-born radionuclides in the contaminated forest ecosystems. Long-term dynamics of the migration processes

•The study analyzes 137Cs and 90Sr biogeochemistry due to the Chernobyl accident.•The study is based on 25 years of forest monitoring around the Chernobyl NPP.•Soil and biota processes were found to control 137Cs cycles in the forest ecosystems.•90Sr cycles in the forest ecosystems are less dependable on biota than 137Cs.

The paper integrates the results of 25-year monitoring study of 137Cs and 90Sr biogeochemical cycle in the forest ecosystems of Russia and Ukraine contaminated due to the Chernobyl accident. The monitoring network was established in 1986 as a number of long-term key sites (KS) located 5 to over 500 km from the Chernobyl NPP. The following components have been monitored: biota (trees, grass and shrubs, mosses, and fungi), soils (forest litter and mineral horizons), soil water, and throughfall. Presently, 25 years after the Chernobyl fallout, 137Cs and 90Sr uptake by vegetation exceed their infiltration through the soil, i.e. biogeochemical cycle currently plays an important role impeding the radionuclide infiltration through soil to the ground water. In wet, accumulative landscapes, biota is a leading factor of the radionuclide cycle, while in dry, eluvial landscapes, soil absorbing complex plays a more important role. The effect of landscape type is manifested for 137Cs, yet less important for 90Sr. 137Cs is actively uptaken by the fungi complex, while 90Sr is primarily accumulated in the arboreal vegetation.Biogeochemical fluxes of 137Cs and 39K in some ecosystems are still different, even 25 years after the fallout.