Journal of Oceanography

, Volume 73, Issue 5, pp 559–570 | Cite as

Processes affecting long-term changes in 137Cs concentration in surface sediments off Fukushima

Special Section: Original Article Radionuclides in coastal sediments after the accident of Fukushima Daiichi Nuclear Power Plant


Temporal changes in cesium-137 (137Cs) concentrations in the surface (0–10 cm) layer of seabed sediment were quantified from continuous observation data at 71 stations within a 150-km radius of the Fukushima Daiichi Nuclear Power Plant, and the primary processes affecting temporal changes were identified. From March 2011 to the end of 2015, about 80% of the initially deposited 137Cs in the surface sediment in the coastal region (bottom depth ≤100 m) region has dissipated (radioactive decay is not included). Such a remarkable change in the 137Cs concentration was not observed in the offshore (>100 m) region. This paper focuses on the following three processes that affected the decrease in the 137Cs concentrations, and assesses their relative importance; (1) resuspension and transport of 137Cs-bound sediment, (2) desorption of 137Cs from the sediment, and (3) dilution of 137Cs by vertical mixing of sediment. Consequently, it was estimated that the first two processes together have potentially contributed to reduce the 137Cs inventory in the top 10 cm of the coastal region by at most 35%. Furthermore, by applying a pulse input sediment mixing model to the observed vertical distribution of sedimentary 137Cs, it was also estimated that more than 43% of the 137Cs in the surface sediment was transported to deeper sediment layers by vertical mixing of the sediment. This indicates that the decrease of 137Cs concentrations in coastal sediments was mainly affected by mixing of 137Cs-bound surface sediment with less contaminated sediment in the deeper layers.


Fukushima Daiichi Nuclear Power Plant accident Radiocesium Sediment Suspended particles Bioturbation Particle-seawater interaction 



The author is grateful to captains, crews and scientists of the R/V Tansei-Maru KT-11-27, KT-13-01, R/V Hakuho-Maru KH-11-07, R/V Shinsei-Maru KS-14-20, KS-15-13 (Univ. of Tokyo/JAMSTEC), and R/V Seikai (JAEA) cruises for their assistance in the fieldwork. The author is also grateful to J. Nishikawa, H. Narita, Y. Kato (Tokai Univ.), T. Aono, M. Fukuda (QST), M. Uematsu, H. Obata (Univ. Tokyo), H. Tazoe (Hirosaki Univ.), M.C. Honda (JAMSTEC), K.O. Buesseler (WHOI), S. Nagao (Kanazawa Univ.), T. Morita, T. Ono, H. Kaeriyama, D. Ambe (Natl. Res. Inst. Fish Sci., Japan), T. Kobayashi, H. Kawamura, T. Nakanishi, E. Takeuchi, M. Watanabe, Y. Kumagai, Y. Segawa, Y. Satoh, M. Nakano, T. Isozaki, M. Nemoto, K. Tobita, M. Nagaoka, M. Hirasawa, and K. Matsumura (JAEA) for their support in the field, laboratory work and their valuable comments. The manuscript was improved by two helpful reviews.

Supplementary material

10872_2017_421_MOESM1_ESM.docx (77 kb)
Supplementary material 1 (DOCX 76 kb)


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Copyright information

© The Oceanographic Society of Japan and Springer Japan 2017

Authors and Affiliations

  1. 1.Research Group for Environmental ScienceJapan Atomic Energy AgencyTokaiJapan

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