[H-CG24] Nuclear Energy and Geoscience

[HCG24-P11] Temporal changes of Cs-137 distributions in forest floor of the evergreen coniferous forests in Fukushima, Japan

*Tadafumi Niizato¹, Keiichi Sasaki², Yukiko Koizumi², Hua Jia², Ryo Okino² (1.Japan Atomic Energy Agency, 2.Mitsubishi Materials Techno Corporation)

Keywords:TEPCO’s Fukushima Dai-ichi Nuclear Power Plant accident, radiocesium, evergreen coniferous forest, forest floor, depth distribution

An understanding of long-term environmental dynamics of radiocesium in forested area, which is released by the TEPCO’s Fukushima Dai-ichi Nuclear Power Plant accident, is a key issue for predicting the future radiocesium distribution and forest products radioactivity, especially for ¹³⁷Cs (hereinafter, Cs) with long half-life of 30 years. In this paper we present the temporal changes of Cs depth distributions in forest floor of the evergreen coniferous forests in Fukushima by applying of a cluster analysis to the Cs depth distribution in the forest floor obtained from 2014 to 2020. The cluster analysis can assemble the investigation sites into relatively homogenous groups with similar Cs depth distribution.
The results show the temporal changes in the Cs amount decreasing in the litter layer and increasing in the soil layer as a general trend. However, distinctly different groups were identified in the same investigation year, such as the group with high Cs amount in the litter layer but low Cs in the soil layer and the groups with low Cs amount in the litter layer but high Cs in the soil layer. This means that the progress of the Cs migration from the litter to soil layers is different in the investigation sites.

[1] Forestry Planning Division of Fukushima Prefecture, Results of the radioactive material investigation, web page of Fukushima Prefecture.
[2] Takahashi et al., 2018, J.Environ.Radiact. 192, 172-180.