[M-AG39] Radioisotope migration: New development for dynamics study of radionuclides from 1F NPP accident

[MAG39-03] Impacts of decontamination and subsequent natural recovery processes on terrestrial systems in the Niiida River basin, Fukushima

★Invited Papers

*Yuichi Onda¹, Bin Feng¹, Yoshifumi Wakiyama², Keisuke Taniguchi³, Asahi HASHIMOTO¹, Zhang Yupan¹ (1.Center for Research on Isotopes and Environmental Dynamics, University of Tsukuba, 2.Institute of Radioactivity, Fukushima University, 3.National Institute of Technology, Tsuyama College)

Keywords:decontamination, Cs-137, suspended sediment

In the Fukushima region, large-scale decontamination in the watershed needs more attention because of its potential impact on the flux of particulate cesium-137 from the terrestrial environment to the ocean. Here, we combine a high-resolution satellite dataset with concurrent river monitoring results to quantitatively assess the impact of land cover change in a large decontaminated area on the dynamics of river suspended solids (SS) and particulate Cs-137 between 2013 and 2018.
The results show that the erodibility of the decontaminated area increases dramatically during the decontamination period and then decreases sharply during the subsequent natural restoration period. The SS dynamics of the river showed a linear response to this land cover change, with the annual SS load (normalized by water discharge) at the end of decontamination increasing by more than 300% compared to that before decontamination, and decreasing by about 48% at the beginning of natural restoration. The variation of particulate Cs-137 concentration well reflects the process of sediment source replacement due to land cover change in the decontaminated area. The "Fukushima Decontamination Experiment" can reveal the dramatic impacts of decontamination and natural restoration processes, and emphasizes the need for quantitative assessment of human impacts on land use and resulting changes in sediment transport patterns in large catchments.