DISTRIBUTION AND RETENTION OF CESIUM AND STRONTIUM IN SWEDISH BOREAL FOREST ECOSYSTEMS

The retention and distribution of cesium, and to some extent strontium , in forest environments are being studied at three sites in Sweden. T he main part of the cesium found in the soil was recovered in horizons rich in organic matter. The cesium was retained in the soil organic m atter in a more or less extractable form. As different soil types have a different distribution pattern of organic matter, the distribution of cesium will depend on the forest soil type. The clay content in Swe dish forest soils is, in general, low which will mitigate the retentio n of cesium in the soil mineral horizons. The cesium and strontium pre sent in the trees was considered to be an effect of assimilation by th e tissues in the canopy as well as by the roots. The redistribution of cesium within the trees was extensive which was considered to be the effect of a high mobility of cesium in the trees. The recovery of stro ntium-90 in pines, in relation to the deposition rate was higher compa red to the relative recovery of cesium-137, 30 years after deposition. The cesium and strontium will remain in the forest environment for a considerable time but can be reduced by forest practice, by leaching o ut of the soil profile or by radioactive decay.