Dynamics of strontium-90 in forest ecosystems

¹ German Federal Office for Radiation Protection, Institute for Radiation Hygiene, Section Radioecology, Ingolstädter Landstrasse 1, 85762 Oberschleissheim, Germany
² German Federal Office for Radiation Protection, Institute for Atmospheric Radioactivity, Rosastrasse 9, 79098 Freiburg, Germany

Abstract

The behaviour of Sr-90 in coniferous forest ecosystems was investigated at three different sites in Bavaria, South Germany. In 1995 and 1996 the Sr-90 activity was measured in about 200 samples, covering different soil horizons and understory vegetation. In addition, the Cs-137 activity was measured for comparison. Sr-90 mainly originates from the fall-out of the nuclear weapons tests during the 50ies and 60ies, the contribution of the Chernobyl accident being considerably lower. The current distribution of Sr-90 within the ecosystem therefore represents the long-term consequence of the dynamic behaviour during the last three to four decades. The results show that the major portion of Sr-90 in forest soil still persists in the organic horizons, indicating a very low migration rate. The qualitatively different vertical profiles of Sr-90 and Cs-137 suggest an efficient transfer from soil to plants and a continuous supply of Sr-90 to the litter horizon via leaf-turnover. The activity levels in edible berries were rarely higher than a few Bq/kg (dw). Sr-90 activities between about 10 and 50 Bq/kg (dw) were measured in other parts of green plants. The uptake of Cs-137 from soil to plants is significantly higher in forests than in agricultural ecosystems, especially on mineral soils. The differences for Sr-90 are less pronounced than in the case of Cs-137.