Year-round variations in the fluvial transport load of particulate 137Cs in a forested catchment affected by the Fukushima Daiichi Nuclear Power Plant accident

IR

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  • 福島第一原子力発電所事故により影響を受けた森林集水域における粒子態137Csの河川移動負荷の通年変動

Abstract

Particulate $^{137}$Cs in stream water was collected continuously for two years in order to assess the long-term trend of the $^{137}$Cs discharge from the forest environment. Sampling was conducted from December 2011 to December 2013 in a mountainous stream, which received the $^{137}$Cs from the Fukushima Daiichi Nuclear Power Plant accident. A seasonal increase in fluvial transport load of particulate $^{137}$Cs associated with suspended solids (SS) was observed in August and September when rainfall was abundant. The particulate $^{137}$Cs concentration decreased at a faster rate than the rate due to radioactive decay. This decrease might be resulted from redistribution of the easily eroded and polluted soil surface due to heavy rain events such as typhoons. These findings indicate that the particulate $^{137}$Cs load was subject to the inter-annual variations in rainfalls, and decreased gradually over a long period of time due to a decrease in $^{137}$Cs concentration in SS.

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