THE FATE OF CHERNOBYL RADIOCESIUM IN THE RIVER ORE CATCHMENT, NORTHERN SWEDEN

A Cs-137-balance for the catchment of the River Ore in central norther n Sweden which received about 30 kBq m(-2) of radiocesium from the Che rnobyl accident was calculated for the period 1986-1991. Altogether, s lightly less than 10% of the total deposition in the catchment was est imated to be exported from the terrestrial parts during this period of time. More than 90% of this loss is transported with the River Ore to the outer sea of the Gulf of Bothnia. The retention in Lake Ortrasket which is the only lake along the river course and the Ore Estuary out side the river mouth was thus slightly less than 10%. Nearly all of th e radiocesium deposited in the lake is permanently retained in the sed iments and successively covered with less radioactive sediment. A cons iderable export of radiocesium from the estuary to the outer sea takes place due to resuspension and subsequent transport by wind and wave g enerated currents.