Spatial distribution of Cs-137 in forest soils of Switzerland

In the framework of the second Swiss forest soil inventory, Cs-137-activity from 172 sites was measured systematically for the first time in the topmo st soil layer (0-5 cm) and represented on a map. The spatial distribution o f Cs-137 contamination was similar to the pattern observed in 1986 from dos e equivalent measurements following the Chernobyl nuclear power plant accid ent. Forest soils from regions with high precipitation in 1986 showed a hig her Cs-137 activity than regions with low precipitation. At sites with high caesium activities it was possible to discriminate between Cs-137 originat ing from global fallout of the fifties and sixties and Cs-137 from the Cher nobyl accident. The results indicate that radiocaesium persists in the top soil layers and is recycled in forest ecosystems.