Retention and horizontal redistribution of sedimentary Chernobyl ¹³⁷Cs in a small Swedish forest lake

Abstract

The horizontal and vertical distribution of sedimentary ¹³⁷Cs was examined in 20 cores to assess the long-term immobilization of ¹³⁷Cs contamination in a small Swedish soft-water lake after the nuclear accident in Chemobyl in 1986. The sediment inventory of ¹³⁷Cs was highly correlated with water depth, demonstrating a substantial net transport of sedimentary ¹³⁷Cs from littoral areas towards the profundal zone of the lake basin. Flux estimates suggest that about half of the ¹³⁷Cs has been removed from the shallow areas within the first six years after contamination, while the inventory in the deepest areas has increased by 50%. Gross loss rates are strongly related to the duration (annual number of days) of lake-water mixing. Wind-driven resuspension is thus suggested to be the main cause of the redistribution and focusing of sedimentary ¹³⁷Cs. The importance of resuspension is confirmed by the horizontal uniformity of ¹³⁷Cs concentrations in surficial sediment and by their similarity to ¹³⁷Cs concentrations in settling material collected in sediment traps.