Modeling transfer of 137Cs fallout in a large Finnish watercourse

In the Finnish environment, lakes provide very important transfer pathways for various pollutants. In this study, a large watercourse was modeled using the dynamic compartment model DETRA. The model includes a fish model for roach, nonpredatory and predatory perches, and pike. Transfer of 137Cs fallout deposited onto the Kymijoki drainage area after the Chernobyl accident was calculated using the model. In the model, fallout was assumed to consist of a soluble and insoluble component, behaving differently in the environment. Model predictions were compared with measured concentrations. Lake Päijänne, the largest lake of the watercourse, was studied most extensively. Calculated concentrations in lake water were consistent with measured concentrations. However, calculated concentrations in fish were lower than measured concentrations. To test the model by using additional experimental data, transfer of nuclear weapons testing fallout was also calculated. The processes that cause the rather rapid removal of 137Cs from lake water need to be studied further using more detailed data. In the long term, runoff and resuspension of sedimentary material were considered to be important in causing concentrations in lake water.