Radiocesium in a Danish pine forest ecosystem

During the autumn of 1991, a Scots pine forest, Tisvilde Hegn, was investigated with respect to the distribution of radiocesium on compartments in the forest ecosystem. The sandy acidic soil is poor, with a approximately 5-cm thick layer of organic soil, and clay content is very low, between 0 and 2%. Cesium from Chernobyl is still totally in the upper 5 cm, while almost half of the fallout cesium has penetrated to depths lower than 5 cm. More than 95% of the total amount of Cs-137 is in the soil compartment. The rest is mainly in the trees (3.4%) and vegetation (0.4%), moss and lichen included. The concentrations of radiocesium are highest in the endshoots of the pine trees, and lowest in the hardwood. There are indications that the Chernobyl cesium is mainly distributed in the parts of the tres that have been formed since 1986. Observed Ratios (OR) were used to characterize the ability of the different components of the forest ecosystem to accumulate radiocesium. OR is defined as the ratio between the content of Cs-137 kg-1 (dry wt.) and the deposition per meter square. In vascular plants, mosses and lichens, OR varied between 0.01 and 0.1 m2/kg. In fungi, it varied between 0.05 and 4.5 m2/kg, though generally it was between 0.2 and 1 m2/kg. OR (Cs-137 kg-1/dry wt. of meat x Cs-137 m-2) levels in three roe deer samples varied between 0.016 and 0.21 kg-1/dry wt. With an annual harvest of around 70 000 animals, this might be the most important pathway of this radionuclide to man from semi-natural ecosystems in Denmark.