Radiocaesium retention in bog meadows: an analysis based on soil properties

The deposition of large amounts of radiocaesium from the Chernobyl Nuclear Power Plant accident (ChNPP,1986) has required a study of the fate of this long-lived radioisotope in ecosystems. Fallout radionuclide becomes incorporated into the soil biogeochemical processes and the human food chain. Usually, meadows located on polluted peat soils are intensively used for sheep and cow grazing, which results in contaminated animal products. Therefore, to suggest remediation methods for contaminated bog meadows it is necessary to find out the key factors affecting the ¹³⁷Cs mobility in bog soils.

The vertical distribution of ¹³⁷Cs in peat bog soils in the remote period after the Chernobyl accident was investigated. The study was conducted on bog meadows in the Bryansk region of Russia. Soil samples were taken at locations on lowland and transitional bogs.

Fifteen years after the accident, an analysis of soils showed that the peak of ¹³⁷Cs activity was still in the upper 10 cm layer. This layer is usually saturated with plant roots. The highest ¹³⁷Cs retention (92% of the total inventory) has been observed in the top 10 cm layer in the drained bog. The findings revealed that elevated soil moisture promotes ¹³⁷Cs downward migration.

The rate of ¹³⁷Cs migration is controlled by the solid-liquid distribution coefficient K_d which is related to the presence of clay minerals and cations competing for exchange sites on solid soil, such as K⁺ and NH₄⁺. In wetlands with the high content of decomposed organic matter are created the conditions for intensive ammonification. This study provides evidence that ammonium is the major contributing factor for K_d values in peat soils on bog meadows.

Remediation methods aimed at enhanced removal of ¹³⁷Cs from the root zone in bog soils are discussed.