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.