RATES OF REMOVAL OF SEDIMENT ASSOCIATED RADIOCESIUM FROM THE PLYNLIMON EXPERIMENTAL CATCHMENTS, POWYS, UK

Inventories of weapons-test and Chernobyl derived Cs-137 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 Cs-137 contrast with that for older weapons-test fallout Cs-137 deposits (0.035-0.36 x 10(-3) y(-1)). These results show that freshly deposited Chernobyl Cs-137 is presently being lost at a significantly higher rate than weapons-test derived Cs-137. For Cs-137 from both sources, residence times in the undisturbed upper Wye catchment are significantly higher than in the afforested upper Severn catchments.