Japan Geoscience Union Meeting 2023

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[J] Oral

A (Atmospheric and Hydrospheric Sciences ) » A-CG Complex & General

[A-CG42] Water and sediment dynamics from land to coastal zones

Tue. May 23, 2023 10:45 AM - 12:00 PM 102 (International Conference Hall, Makuhari Messe)

convener:Keiko Udo(Department of Civil and Environmental Engineering, Tohoku University), Yuko Asano(The University of Tokyo), Shinichiro Kida(Research Institute for Applied Mechanics, Kyushu University), Dai Yamazaki(Institute of Industrial Sciences, The University of Tokyo), Chairperson:Yuko Asano(The University of Tokyo), Dai Yamazaki(Institute of Industrial Sciences, The University of Tokyo)

11:45 AM - 12:00 PM

[ACG42-10] Impact of Fukushima decontamination on soil erosion and suspended sediment to downstream

★Invited Papers

*Yuichi Onda1, Bin Feng2, Keisuke Taniguchi3, Yoshifumi Wakiyama4, Asahi Hashimoto1, Yupan Zhang1 (1.Center for Research on Isotopes and Environmental Dynamics, University of Tsukuba, 2.TU. Wien, 3.National Institute of Technology, Tsuyama College, 4.Institute of Environmental Radioactivity, Fukushima University)

Keywords:Cs-137, suspended sediment, decontamination

Government-led decontamination has significance in reducing radiation risk and recovering fallout-137Cs contaminated soil for Fukushima regions, yet the long-term downstream impacts of land-use changes in large-scale decontaminated regions remain unclear. Here we provide the first comprehensive assessment of decontamination impacts during 2013–2018 by combining the governmental decontamination data, high-resolution satellite images, and concurrent river monitoring results. We find that the regional erodibility drastically increased during the decontamination stage but rapidly decreased in the subsequent natural restoration stage. River SS dynamics exhibited good responses to this erodibility shift and downstream normalise SS load had ~ 240% increase by the end of decontamination. The contribution of 137Cs-free sediment from decontaminated regions increased gradually with decontamination (maximum 71%), causing a rapid decline in particulate 137Cs concentration. After decontamination, although the rapid vegetation regrowth in decontaminated regions made catchment sediment yield diminished and downstream sediment source composition altered, the combined effect of above variations resulted in almost constant downstream normalised 137Cs flux into the ocean. Our findings highlight the need to comprehensively assess the impacts of land-use changes induced by strong perturbation on land-ocean sediment transfer patterns and their unsustainable consequence in downstream environment.