Post-depositional redistribution and gradual accumulation of 137Cs in a riparian wetland ecosystem in Sweden

After the Chernobyl accident, high activity concentrations of Cs-137 (>1 MBq m(-2)) Were detected in riparian swamp in the central-eastern part of Sweden. The objective of this Study was to clarify the rea distribution processes behind the accumulation of Cs-137 in the wetland. A mass balance budget of Cs-137 was calculated based oil soil and sediment samples and reports in the literature. Results showed that accumulation Occurred over several years. Of all the Cs-137 activity discharged between 1986 and 2002 from the upstream lake, 29% was estimated to be retained in the wetland. In 2003, measurements showed that 17 kBq m(-2) sedimented on the stream banks of the wetland. Continuing overbank sedimentation by spring flooding prolongs the time that the wetland will contain high activity concentrations Of Cs-137. Con sequently, organisms living in wetlands serving as sinks for Cs-137 may become exposed over long time periods to high activity concentrations. (C) 2005 Elsevier Ltd. All rights reserved.