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[MAG34-01] Changes in the behavior of dissolved Cs-137 from headwaters to downstream in the Kuchibuto River catchment
Keywords:Particulate Cs-137, Dissolved Cs-137, Organic Matter
The Fukushima Daiichi Nuclear Power Plant accident on March 11, 2011, resulted in the release of large amounts of radioactive cesium-137 (137Cs) into the environment. Therefore, it is essential to study the dynamics of Cs-137 in the entire river, from the headwaters downstream. The concentration of suspended Cs decreased significantly after decontamination in evacuated areas (Feng et al., 2022). This rapid decrease in suspended Cs-137 concentration can be used to identify the source of dissolved Cs. Therefore, we attempted to evaluate whether the dissolved form Cs-137 was derived from organic matter or suspended solids by comparing data before and after decontamination
The study area consisted of four water source basins and four river basins (eight sites in total) in the Kuchibuto River watershed in the Yamakiya district of Fukushima Prefecture, located approximately 35 km northwest of FDNPP. In the Kuchibuto River watershed, the concentration of suspended solid Cs-137 rapidly decreased in the decontaminated areas in the headwaters and upstream areas because of a large influx of decontaminated soil with low Cs-137 concentrations caused by an increase in bare land due to decontamination. However, no apparent effect of decontamination was observed on the concentrations of dissolved Cs-137 and Cs-137 in the coarse organic matter. Comparing the slopes of the Cs-137 concentrations in suspended solids, dissolved solids, and coarse organic matter, the slope of dissolved solids was similar to that of coarse organic matter in the headwaters. The slope of the SS was similar to that of SS in the downstream areas. These results suggest that the contribution of dissolved Cs-137 from organic matter in small watersheds and suspended solids in large watersheds was more significant.
The study area consisted of four water source basins and four river basins (eight sites in total) in the Kuchibuto River watershed in the Yamakiya district of Fukushima Prefecture, located approximately 35 km northwest of FDNPP. In the Kuchibuto River watershed, the concentration of suspended solid Cs-137 rapidly decreased in the decontaminated areas in the headwaters and upstream areas because of a large influx of decontaminated soil with low Cs-137 concentrations caused by an increase in bare land due to decontamination. However, no apparent effect of decontamination was observed on the concentrations of dissolved Cs-137 and Cs-137 in the coarse organic matter. Comparing the slopes of the Cs-137 concentrations in suspended solids, dissolved solids, and coarse organic matter, the slope of dissolved solids was similar to that of coarse organic matter in the headwaters. The slope of the SS was similar to that of SS in the downstream areas. These results suggest that the contribution of dissolved Cs-137 from organic matter in small watersheds and suspended solids in large watersheds was more significant.