EGU2020-13220, updated on 20 Jan 2021
https://doi.org/10.5194/egusphere-egu2020-13220
EGU General Assembly 2020
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Temporal changes of the radiocesium activity concentration in river bottom sediment and suspended sediment in Eastern Japan

Yuichi Onda1, Chen Tang1, Xiang Gao1, Yukio Takeuchi1,2, Keisuke Taniguchi2, Momo Kurihara1,3, and Katsumi Hirose1
Yuichi Onda et al.
  • 1University of Tsukuba, Center for Research in Isotopes and Environmental Dynamics, Tsukuba, Japan (onda@geoenv.tsukuba.ac.jp)
  • 2Fukushima Prefectural Centre for Environmental Creation, Miharu, Fukushima, Japan
  • 3National Institutes for Quantum and Radiological Science and Technology, Chiba, Japan

We examined the temporal trend of Cs-137 concentration of river sediment and suspended sediment in Eastern Japan areas from September 2011 to January 2017. We used 716 monitoring data by the Ministry of the Environment from 461 sites and applied particle size correction to eliminate the influence of changes in particle size distribution in the concentration of Cs-137. Also, in some locations, we also compared the activity concentration of suspended sediment and dissolved water in Cs-137 and compared.    The results showed that Cs-137 concentration decreased through the study period in most sites, and the average declining, λ, is about 0.168 in the 2013-2018 period. In some sites increasing trend or larger rate of decline were found, but these locations are limited to lower contaminated catchments (less than 50k Bq/m2). The particle size corrected Kd value of the bottom sediment (Kd ac) shows around 10-4 to 10-5 Kg/L, but varied significantly where the initial catchment inventories are less than 50 kBq/m2. In most sites,  Cs-137 concentration on the particle size corrected Suspended sediment and bottom sediment show similar values, except for some specific sites (such as near the coast, etc).  These data imply that the activity concentration of dissolved Cs is important to control the rate and processes of interaction of dissolved radionuclides with the bottom sediment interface layer in the river environment affected by the Fukushima fallout.

How to cite: Onda, Y., Tang, C., Gao, X., Takeuchi, Y., Taniguchi, K., Kurihara, M., and Hirose, K.: Temporal changes of the radiocesium activity concentration in river bottom sediment and suspended sediment in Eastern Japan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13220, https://doi.org/10.5194/egusphere-egu2020-13220, 2020

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Display material version 1 – uploaded on 07 May 2020
  • CC1: Comment on EGU2020-13220, Olivier Evrard, 08 May 2020

    Many thanks, Onda-sensei, for sharing this impressive data treatment. I wondered what was your interpretation of the reasons explaining the limited change in the Cs-137 concentrations in sediment collected in the Ota River (as an example)? Thanks for your feeback! Best wishes, Olivier Evrard

    • AC1: Reply to CC1, Yuichi Onda, 08 May 2020

      Dear Olivier,

      Thank you for your question. We are now checking the detailed catchment inventory distribution in the catchment, and like ota river, the upstream higher Cs... catchment can affect the delayed decline.. but not sure so far!! we will discuss later!

       

      • CC2: Reply to AC1, Olivier Evrard, 08 May 2020

        Thanks for your feedback. Maybe the dominance of forests in upper catchment parts also contributes to explain this? Talk to you later, best wishes! Olivier