A generic dynamic model of Cs-137 turnover in Nordic Lakes

The purpose of this study was to design a generic model for long-term predictions of the Cs-137 concentration in lakes, emphasizing the secondary load of radiocaesium to the waterbody from lake sediments and drainage area. If the concentration of Cs-137 in lake waters can be accurately predicted, estimates of concentration in fish will be more reliable. The inflow from the drainage area is estimated from the fraction of outflow areas, whereas resuspension from lake sediments is estimated from the maximum depth and surface area. The model is based on compartment theory. Modelling results for six lakes are presented. There was very good agreement between model results and observed values, for both water and lake sediments, although there were minor discrepancies for sediments in the deepest lakes. Analyses of the model results showed that, for deep lakes, the main contribution maintaining the concentration in lake waters is inflows from the drainage area, whereas for shallow lakes, the main factor is resuspension for caesium rich sediments.