FRACTIONATION OF CESIUM ISOTOPES AND SR-90 IN SNOWMELT RUN-OFF AND LAKE WATERS FROM A CONTAMINATED NORWEGIAN MOUNTAIN CATCHMENT

Cesium isotopes and Sr-90 have been determined in the inflow and outflow rivers of a Norwegian subalpine lake. The lake is situated in an area contaminated by Chernobyl fallout. Sampling was carried out during the spring peak discharge period associated with snowmelt. Transported coarse particulate plant material was collected by traps. Particles and colloids were removed from water samples by hollow fibre ultrafiltration. The results illustrate that run-off during the spring snowmelt is an important pathway for these radionuclides. The cesium isotopes are predominantly transported as colloids, while Sr-90 is present in the form of low molecular weight mobile species. Based on lake budget calculations, more than 50% of the cesium input is retained in the lake, while more than 90% of the Sr-90 is transported through the lake and into lower parts of the drainage system.