Reservoir sediments as a long-term source of dissolved radiocaesium in water system; a mass balance case study of an artificial reservoir in Fukushima, Japan

Funaki, Hironori ; Sakuma, Kazuyuki   ; Nakanishi, Takahiro   ; Yoshimura, Kazuya  ; Katengeza, E. W.*

This study provides new insights regarding to the long-term temporal change and the mass balance of dissolved Cs in an artificial reservoir affected by the Fukushima Dai-ichi Nuclear Power Plant accident. Time-series water samples were collected from 2014 to 2019 for Cs concentration measurements in and around Ogaki Dam Reservoir in which the catchment has a high Cs inventory. We revealed that the arithmetic mean of dissolved Cs concentration was significantly higher in the output water than in the main input water, and the effective ecological half-live of dissolved Cs of the output water was longer than that in the main input water. Remarkably, it is considered that the output dissolved Cs was significantly larger than the total input dissolved Cs. Reservoir sediments containing high Cs activity may become even more important in the future as sources of bioavailable dissolved Cs.