The characterization of radiocaesium transport and retention in Nordic lakes

Fractionation studies of radiocaesium have been carried out in three Nordic lakes, Oevre Heimdalsvatn in Norway, Hillesjoen in Sweden and Saarisjaervi in Finland. These lakes differ markedly in several aspects and provide insight into the factors determining radionuclide transport in a range of lake ecosystems. Transport of 137Cs in plant material (Coarse Particulate Organic Matter, CPOM) was about 17 times greater to Oevre Heimdalsvatn than Saarisjaervi, although over 99% of the inflow CPOM was retained in both lakes. Inflows to Hillesjoen were an order of magnitude lower than to Saarisjaervi and the net retention was only 71%, on account of the outflow of autochthonous production, largely water lily fragments. With regard to the water phase, the lakes differed in the activity of 137Cs in the various molecular weight fractions. This was a function of catchment processes, resuspension and biological activity in the lakes. In Oevre Heimdalsvatn and Saarisjaervi 45% of the 137Cs in the water phase was retained in the lake, while in Hillesjoen ten times more 137Cs in the water phase was retained in the lake, while in Hillesjoen ten times more 137Cs flowed out than flowed in, due to resuspension of 137Cs-rich sediments. (orig.)