[3J09-12] Fukushima 2

[3J10] Investigation on distribution of radioactive substances in Fukushima

(10) Dynamic change of dissolved Cs-137 from headwater to the lower reaches of the Kuchibuto River basin

*Yuichi Onda Onda¹, Taichi Kawano¹, Junko Takahashi¹, Hiroaki Kato¹ (1. Center for Research in Radiation, Isotopes and Earth System Sciences)

Keywords:Cs-137, Dissolved Cs-137, decontamination, Suspended sediment, Organic Matter

The Fukushima Daiichi Nuclear Power Plant accident in 2011 released a large amount of radioactive cesium 137 (137Cs) into the environment. Most of it was deposited in forested areas and then transferred to the environment through river systems. The dynamics of 137Cs from headwaters to downstream areas need to be clarified. Previous studies have focused on dissolved and suspended forms of 137Cs but haven't compared their sources. Seasonal variations of dissolved 137Cs are influenced by water temperature and organic matter decomposition, but research in organic-rich headwater sub-watersheds is lacking. Decontamination reduces suspended 137Cs concentrations, providing a way to differentiate between dissolved and suspended forms. This study aims to examine the interrelationships between dissolved, suspended, and coarse organic matter 137Cs concentrations and seasonal variation factors. The findings indicate the significant contribution of dissolved 137Cs leaching from organic matter in small catchments and suspended sediment in the lower reaches of the river.