Post-Chernobyl radiomonitoring of Ukrainian forest ecosystems

More than 20 experimental sites in different directions out from the Chernobyl nuclear power plant in the Ukrainian territory were established as a network to study the migration of radionuclides in forest ecosystems. The depth distributions of ¹³⁷Cs and ⁹⁰Sr in the surface layer of forest litter and soil for characteristic types of Ukrainian coniferous and deciduous forests have been studied in detail. The bulk of the activity occurs in the top 15 cm of the soil profile. Sequential extraction experiments have identified that the major part of radiocaesium is in a fixed, unexchangeable form. Soil profiles indicate no substantial differences for 1991 and 1992 suggesting that ¹³⁷Cs has a limited mobility.