Radiocaesium removal from European lakes and reservoirs: key processes determined from 16 Chernobyl-contaminated lakes

A study based on information from the scientific literature was carried out to identify the key processes which determine the initial radiocaesium activity concentration and its rate of removal in 16 different European lakes after the Chernobyl accident. Analysis and modelling of these data showed that a simple model, incorporating only dilution, lake flushing and settling of suspended particles, can explain 97% of the variation in initial activity concentrations in lakewater and 79% of the variation in ¹³⁷Cs removal rates. On the basis of currently available data, incorporating a simple model for removal of activity by diffusion across the sediment-water interface did not improve model predictive power. It is shown that direct diffusion was of less importance in determining radiocaesium removal rates than particle settling. The potassium concentration of the lakewater was found to have a significant, negative, covariance with ¹³⁷Cs removal rates. The relationship between [K⁺] and removal rate is shown to be quantitatively consistent with previous studies on the binding mechanism of ¹³⁷Cs to particulates.