Distribution of cesium-137 in Japanese forest soils: Correlation with the contents of organic carbon

The spatial and vertical distributions of Cs-137 in surface soils were surv eyed and analyzed then correlated with the contents of organic carbon in th e hinoki (Chamaecyparis obtusa Sieb. et Zucc.) plantation forest and second ary forest dominated by red pine (Pinus densiflora Sieb. et Zucc.) in Japan . The spatial variation of Cs-137 activity was observed in the surface soil around the red pine. The average activity of 16 samples around the tree is 42.4 Bq/kg and the standard deviation is 25.9 Bq/kg. This finding indicate s the importance in the selection of a sampling site and the number of samp les from the surface soils especially around a tree. For the vertical distr ibution of Cs-137 activity, it was found that the concentration in the surf ace soil is highest, 149 Bq/kg in the hinoki stand and 101 Bq/kg in the red pine stand, and decreases with depth. The relationship between Cs-137 acti vity and carbon content in the forest soil was investigated in two undistur bed forest stands. The relations were more precisely expressed using an exp onential equation than by a linear equation. From the same forest, similar regression equations were obtained. This indicates that the distribution of Cs-137 could be characterized by the organic carbon content in an undistur bed forest. It is also suggested that the coefficient values in the regress ion equation help to define the movement of Cs-137 accompanying the decompo sition of organic matter. (C) 1998 Published by Elsevier Science B.V. All r ights reserved.