Rates of removal of sediment associated radiocaesium from the plynlimon experimental catchments, Powys, UK

Inventories of weapons-test and Chernobyl derived (137)Cs within the upper Wye and upper Severn catchments have been estimated using a variety of techniques. Transport rates of radiocaesium from the catchments have been determined from measurements of radionuclide activities on suspended and bedload sediments. Radiocaesium transport coefficients calculated from the results of 0.46-5.42 x 10(-3) y(-1) for freshly deposited Chernobyl (137)Cs contrast with that for older weapons-test fallout (137)Cs deposits (0.035-0.36 x 10(-3) y(-1)). These results show that freshly deposited Chernobyl (137)Cs is presently being lost at a significantly higher rate than weapons-test derived (137)Cs. For (137)Cs from both sources, residence times in the undisturbed upper Wye catchment are significantly higher than in the afforested upper Severn catchments.