Spatial Distribution of 137CS in Forest SOils of Switzerland

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