DISTRIBUTION OF CS-137 IN SURFACE SOILS AS AFFECTED BY FOREST CLEAR-CUTTING

The distribution of Cs-137 was Studied in podzol soil profiles from a 5 year old forest clear-cut area and an adjacent mature spruce forest in central Norway in order to assess the effects of clear-cutting on t he distribution and mobility of radiocaesium in surface soils. A disti nctly higher radiocaesium activity observed in the humus layer from th e clear-cut compared to the forest area strongly indicates an increase in organic surface soil Cs-137 activity within the first 5 years foll owing forest clear-cutting. Such an increase, previously observed for Ca, Mg, Mn and Zn, is explained by increased supply of radiocaesium fr om decomposing logging residue, such as lichens and needles. Roughly 2 5% of the activity leached from decomposing residue had been transport ed into the A-E layer 5 years after clear-cutting. High Cs-137 activit y in the eluvial (E) horizon and a distinct decrease in deeper horizon s indicates a certain leaching of Cs-137 from the humus layer into the E horizon, which may act as an effective barrier against further leac hing of radiocaesium. (C) 1998 Elsevier Science Ltd. All rights reserv ed.