Spatial and depth distribution of radiocaesium in near-coastal sediment cores of Fukushima Prefecture

福島県沿岸域における堆積物コア中の放射性セシウムの空間及び深度分布について

Chaboche, P.-A.*; 脇山 義史*; 高田 兵衛*; 和田 敏裕*; Evrard, O.*; 御園生 敏治   ; 尻引 武彦; 舟木 泰智 

Chaboche, P.-A.*; Wakiyama, Yoshifumi*; Takata, Hyoe*; Wada, Toshihiro*; Evrard, O.*; Misono, Toshiharu; Shiribiki, Takehiko; Funaki, Hironori

Following the Fukushima-Daiichi Nuclear Power Plant (FDNPP) accident in March 2011, large quantities of radionuclides in general, and radiocaesium (Cs) in particular, were emitted in terrestrial and marine environments of Fukushima Prefecture. Although Cs activity in these environments has decreased since the accident, the secondary inputs via the rivers draining and eroding the main terrestrial radioactive plume were shown to sustain high level of Cs in riverine and coastal sediments, which are likely deposited off the coasts of the Prefecture. Accordingly, quantifying the riverine sources of sediment deposited along the coast and characterizing its spatial and depth distribution, as well as its physico-chemical properties, is of the utmost importance to ensure the safety of fishery products and anticipate the environmental fate of radiocaesium. To conduct this project, coastal sediment cores (n=6) from 26 to 60cm depth were collected during cruise campaigns between July and September 2022 at the Ota, Niida and Ukedo river mouths. In this presentation, we report preliminary results regarding the spatial and depth distribution of radiocaesium activities in these sediment cores. Finally, we will discuss the main challenges identified so far to design and implement a sediment tracing method along the coast of the Fukushima Prefecture.