Thirty-Year Prediction of Cs-137 Supply from Rivers to Coastal Waters off Fukushima Considering Human Activities

The Fukushima Daiichi Nuclear Power Plant accident caused an accumulation of Cs-137 in coastal sediment. The Cs-137 supply from rivers to the ocean can affect the long-term fate of Cs-137 in coastal sediment. Since the Fukushima coastal river basins include large decontaminated and evacuation order areas, considering the decontamination work and resumption of agriculture is important for predicting the Cs-137 supply. We conducted a 30-year prediction of the Cs-137 supply from the Fukushima coastal rivers to the ocean using a distributed radiocesium prediction model, considering the effects of human activities. In river basins with decontaminated and evacuation order areas, human activities reduced the total Cs-137 outflow from agricultural lands, urban lands, and forest areas to the rivers and the Cs-137 supply to the ocean by 5.0% and 6.0%, respectively. These results indicated that human activities slightly impacted the Cs-137 outflow and supply. The Cs-137 supply from rivers impacted by the accident to the coastal sediment was estimated to correspond to 11-36% of the total Cs-137 in the coastal sediment in the early phase of the accident. Therefore, the Cs-137 supply from rivers to the ocean is important for the long-term behavior of Cs-137 in coastal sediment.

Automated summary

The Fukushima Daiichi Nuclear Power Plant accident resulted in the accumulation of Cs-137 in coastal sediment. The supply of Cs-137 from rivers to the ocean has an impact on the long-term fate of Cs-137 in coastal sediment. Human activities, such as decontamination work and agriculture, slightly reduce the outflow and supply of Cs-137 from rivers. The estimated Cs-137 supply from rivers to the coastal sediment corresponds to 11-36% of the total Cs-137 in the early phase of the accident, highlighting its importance.