Factors affecting radiocesium concentration in sediment off Fukushima; Lateral transport of suspended particles

Otosaka, Shigeyoshi*  ; Suzuki, Takashi  ; Tsuruta, Tadahiko  ; Misono, Toshiharu   ; Mino, Yoshihisa*; Sukigara, Chiho*; Ito, Yukari*; Shirai, Kotaro*; Sugihara, Naoko*

In order to clarify the transport process of suspended radiocesium from the coast to the offshore area, which is one of the processes that change the concentration of radiocesium in sediments off Fukushima, a time-series sediment trap was deployed from October 2017 to June 2018 at a station located in southeast of the Fukushima Daiichi Nuclear Power Plant. Sinking particles of 39 periods were collected by this experiment. Cs was detected from sinking particles throughout the observation period, and the concentration showed clear seasonal variation. The maximum Cs concentration was an order of magnitude higher than that in the surface sediment (0-1 cm layer) at the station. On the other hand, the observed annual sinking flux of Cs was less than 1% of the Cs inventory in the seabed column. From these results, it can be concluded that the transport of Cs-bound particles from the coastal area has a relatively small effect of changing the abundance of radiocesium in sediments.