RETENTION AND HORIZONTAL REDISTRIBUTION OF SEDIMENTARY CHERNOBYL CS-137 IN A SMALL SWEDISH FOREST LAKE

The horizontal and vertical distribution of sedimentary Cs-137 was examined in 20 cores to assess the long-term immobilization of Cs-137 contamination in a small Swedish soft-water lake after the nuclear accident in Chernobyl in 1986. The sediment inventory of Cs-137 was highly correlated with water depth, demonstrating a substantial net transport of sedimentary Cs-137 from littoral areas towards the profundal zone of the lake basin. Flux estimates suggest that about half of the Cs-137 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 Cs-137. Th, importance of resuspension is confirmed by the horizontal uniformity of Cs-137 concentrations in surficial sediment and by their similarity to Cs-137 concentrations in settling material collected in sediment traps.