[A-HW18] Material transportation and cycling at the land-sea interface: from headwaters to the ocean

[AHW18-P16] Temporal changes of dissolved radiocesium concentrations in rainwater, soil water, and stream water in forests in Fukushima, Japan

*Masahiro Kobayashi¹, Toshihide Hiruta², Masanobu Hashimoto², Tetsuo Oonuma², Yoshiki Shinomiya¹, Yuko Itoh¹, Yasuhiro Ohnuki¹ (1.Forestry and Forest Products Research Institute, 2.Fukushima Prefecture)

Keywords:Forest, rdiocesium

A wide area of forested land in eastern Japan was contaminated by radiocesium after the accident of the Fukushima Daiichi Nuclear Power Plant in 2011. It is known that radiocesium entering the forest from the atmosphere is mostly transported from the canopy to the forest floor within a few years, and is strongly trapped in the mineral soil, with limited runoff into the stream. Since dissolved radiocesium is readily absorbed by living organisms, it is particularly important to clarify its dynamics. We have been monitoring temporal changes in Cs-137 concentrations in precipitation, soil water, and stream water since the early stage after the accident in in the deciduous broadleaf forest and coniferous evergreen forest.
The Cs-137 concentrations in throughfall, litter leachate, soil water, and stream water decreased markedly in the initial period, and the decrease trend slowed down in the latter period. The Cs-137 concentrations in throughfall and litter leachate were almost the same in the deciduous broadleaf forest, whereas the concentrations in litter leachate were higher in the coniferous evergreen forest. The Cs-137 concentrations decreased significantly while infiltration through the soil, with similar concentrations in stream water and soil water at a depth of 30 cm.