The
137Cs concentration in an undisturbed upper layer of naked land in Fukuoka Prefecture decreased exponentially from 1969 to 1999 with the apparent half-life of 7 years. The ratio of
137Cs concentration in the lower layer of the soil to that in the upper layer was about 1/5. The concentration of
137Cs,
40K, and stable Cs and the soil profile consisting of loss on ignition, pH, and electric conductivity were determined in the 48 samples collected in the forests and the neighboring naked land from 1991 to 1998. The
137Cs concentration in the forest soils ranged from 1 to 424Bq/kg dry wt, 131Bq/kg dry wt on average, although 137Cs was hardly detected in the naked soil around the forest. There was no regional difference in the distribution of the
137Cs concentration, and it varied with pH and electric conductivity in the soil. Further, it tended to be higher in the deciduous woodland than in the evergreen woodland.
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