2023 Volume 22 Issue 2 Pages 59-72
In this report, we describe the results of a survey on the concentrations of radioactive Cs (R-Cs) in forest floor soils and leaves of trees in the forests, from 7 to 9 years after the accident at the Fukushima Daiichi Nuclear Power Plant (FDNPP). The survey areas were three natural forests mainly composed of deciduous broad-leaved trees in the Iitate village, Fukushima Prefecture. More than 7 years after the FDNPP accident, relatively higher concentrations of 137Cs have been detected in leaves of deciduous broad-leaved trees, despite the concentrations of 137Cs becoming established in the soil surface layer, particularly immobilized in frayed edge sites within clay minerals. From 2018 to 2020, the annual flux of 137Cs in the litterfall in the Shimohiso survey area was estimated to be about 5.2 kBq·m−2·year−1. In this survey area, the circulation of R-Cs is still active at a level comparable to and observed in the litterfall produced in the coniferous forest after the FDNPP accident.
