FORURENS: Importance of climate and chemical composition of precipitation on distribution and behaviour of radiocaesium in terrestrial ecosy

Measurements of 137Cs in natural soils in Norway show that the residence time of the radionuclide in the organic-rich surface layer varies much between different parts of the country. Faster removal of Cs from the surface soil in coastal areas suggests th at Cs exchange with marine cations such as Mg++ plays an important role in the transfer of 137Cs to deeper soil layers where it is not plant available. The studies also indicate that H+ and NH4+ ions from transboundary air pollution play a similar role in the southern part of Norway. In this project field investigations of relations between 137Cs and soil chemistry parameters will be carried out at four birch forest sites representing extremes in precipitation chemistry and air pollution influence. Two o f them will be in areas important for reindeer herding, as the results may be particularly valuable for the ongoing management of Chernobyl fallout in reindeer husbandry. Soil columns from all sites will be placed in lysimeters and subjected to leaching e xperiments in the laboratory with different precipitation qualities. Results from the leaching experiments will be compared with evidence from the field studies. Studies of radionuclides in terrestrial ecosystems are traditionally descriptive and based o n measured radionuclide activities in soil and biota. Relatively few studies on influence of chemical processes on the fate of radionuclides in natural soils have appeared. Moreover very few if any of these studies dealt with birch forest, an important ha bitat for sheep and reindeer in Norway. The present project will add considerably to the current knowledge on the soil chemistry of Cs in general and particularly in organic-rich surface soils. Moreover the results will contribute to improved nuclear prep aredness through improved predictions of 137Cs transfer to grazing animals at different climatic conditions. Last but not the least altered 137Cs behaviour as a consequence of climate change may be assessed.