Tsuruta, T.; Shiribiki, T.; Misonou, T.; Nakanishi, T.; Sanada Y., and Urabe, Y., 2021. Vertical profiles of radioactive Cs distributions and temporal changes in seabed sediments near river mouth in coastal area of Fukushima prefecture. In: Lee, J.L.; Suh, K.-S.; Lee, B.; Shin, S., and Lee, J. (eds.), Crisis and Integrated Management for Coastal and Marine Safety. Journal of Coastal Research, Special Issue No. 114, pp. 320–324. Coconut Creek (Florida), ISSN 0749-0208.

Understanding the features of radioactive Cs (137Cs) in seabed sediments in coastal areas linked with rivers, which are major settlement areas for particulate 137Cs, is a key issue in evaluating the supply of 137Cs from river discharges. The vertical profile of 137Cs distribution in seabed sediments is an important clue for elucidating the settlement process of particulate 137Cs near river mouth. Therefore, we sampled seabed sediments using a long core sampler (vibrocoring; the maximum lengths of the core was approximately 100 cm) to clarify the entire vertical profile of the 137Cs distribution and changes in seabed sediments near the river mouth in the coastal area of Fukushima Prefecture. From 2014 through 2019, the 137Cs concentration along the entire vertical profile did not increase, and there was no remarkable migration of the 137Cs toward the deeper layers of the seabed sediments. On the contrary, the amount of 137Cs decreased by more than 70% throughout the entire depth, and the 137Cs distributions in the depth direction become uniform. These results suggest that the supply of 137Cs from the river discharge is not a major concern near the river mouth in the coastal area of Fukushima Prefecture. Resuspension of particle-bound 137Cs and offshore transport are the main factors that reduce the 137Cs concentration in the coastal seabed sediments.

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