Land-sea transport of suspended radionuclides

Otosaka, Shigeyoshi*  ; Misono, Toshiharu   ; Dohi, Terumi   ; Tsuruta, Tadahiko  ; Suzuki, Takashi  

In the coastal sediment off Fukushima, radionuclide-bound suspended particles are continuously supplied from the land through rivers, and the relative amount of the riverine input of the radionuclides in the coastal area increases with time. In the collaborative project in FY2019, we analyzed the characteristics of sinking particles collected at the shelf edge region (bottom depth: 200 m) southeast of the Fukushima Daiichi Nuclear Power Station, and outlined the transport processes of the particulate radionuclides in the coast to the offshore sea area. In FY2020, the reservoir effect of particulate radionuclides in the estuary and coastal areas were examined by conducting analysis of sinking particles in the nearshore and comparing the results with the characteristics of the shelf edge particles. The EPMA analysis of the nearshore particles found that almost no organic particles preserved in the estuary. It was considered that the organic particles found in the shelf edge area were either quickly removed from the estuary by horizontal transport or produced by organisms on the offshore surface.