Radiocesium mobility in the environment after the Fukushima Dai-ichi Nuclear Power Plant accident; Simulation study on Cs behavior in brackish lake, Matsukawa-ura Lagoon

Sakuma, Kazuyuki   ; Misono, Toshiharu   ; Funaki, Hironori ; Watanabe, Yusuke  ; Kurikami, Hiroshi  ; Yamada, Susumu  ; Machida, Masahiko  ; Yoshimura, Kazuya  ; Nakanishi, Takahiro   ; Tsumune, Daisuke*; Tsuji, Hideki*; Hayashi, Seiji*

Understanding how the environmental changes between freshwater and brackish water affect Cs behavior in the environment is crucial because salinity affects Cs dissolution from sediment. The study site is Matsukawa-ura Lagoon, which is located in Soma, Fukushima, Japan. In this study, we simulated water, sediment, and particulate and dissolved Cs transport in brackish water considering boundary conditions of the river inflows and ocean using a 3-dimensional ocean circulation model, 3D-Sea-SPEC. The simulation results for water velocity, temperature, and salinity as well as suspended solids concentrations were in good agreement with the observation results. Also, the simulation results indicate that Cs elution from sediment in the brackish lake affects dissolved Cs concentration in brackish water under base flow conditions; however, the particulate Cs from river discharges could affect dissolved Cs concentrations in brackish water after storm flow conditions.