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.