Factors affecting distribution of radiocesium in sediment off Fukushima, 1; Vertical mixing of sediment

Otosaka, Shigeyoshi

no journal, , 

Based on monitoring data at 71 stations off Fukushima, changing tendencies of radiocesium concentration in sediment are analyzed, and the effect of vertical mixing of sediment on the temporal changes is discussed. In the coastal region (water depth 100 m), inventories of radiocesium in the upper sedimentary layer (0-10 cm) decreased at about 30% per year. In the offshore regions, no significant change in the inventory of sedimentary radiocesium was observed. Vertical profiles of radiocesium in sediment were slightly changed with time, and it indicated transport of radiocesium to the lower sedimentary layers. This downward transport of radiocesium agreed with simulated result by a pulse input model. From these results, we concluded that most of the sedimentary radiocesium derived by the accident of Fukushima Daiichi Nuclear Power Plant is staying in the original location and is gradually transported to the lower sedimentary layers by vertical mixing of sediment.