COMPARISON ~(137)CS VERTICAL DISTRIBUTION CHARACTERISTICS OF TAKIZAWA RESEARCH FOREST AFTER FUKUSHIMA ACCIDENT: A TWO-YEAR FOLLOW-UPSTUDY

摘要

After the Fukushima Dai-ichi nuclear accident, radioactive cesium was released in all the northeast forest area of Japan. We chose three types of forest area (Japanese cedar, Japanese Oak, Mixed forest) and sampled separately with the depth which is located northeast side of Fukushima shows similar meteorological pattern and soil characteristics. Especially we compared 2 year's changes of the vertical distribution of radioactive cesium. Based on the results, vertical movement pattern of radioactive cesium was varied with forest species and geological conditions. Especially considerable percentages of ~(137)Cs exist in litter of Japanese Oak tree had already moved down to next soil layer after 1.6year and this continued after 2.6year. But in Japanese cedar case, radioactive cesium mainly still remains in upper organic layer accompanying additional input of cesium was observed even after 2.6year.Meanwhile, downward migration rate of ~(137)Cs of three type of forest area were very higher and seems to be approximately similar around 1.1-1.7 cm/year because of high porosity and lower bulk density. But this pattern was delayed after second sampling occasion ranged from 0.9 to 1.05. And vertical migration rate of FDNPP(Fukushima Daiich Nuclear Power Plant)-derived is 10～12 times higher than that of NWT(Nuclear weapon test, 0.12～0.13 cm/year)-derived one.