[A-HW27] 流域の水及び物質の輸送と循環－源流域から沿岸域まで－

[AHW27-P08] 農業用ため池における水中の放射性セシウムのモニタリング

*久保田 富次郎¹、申 文浩²、濵田 康治¹、人見 忠良¹ (1.農村工学研究所、2.東北農業研究センター)

キーワード：放射性セシウム, ため池, 農業用水

Radioactive materials were released over wide areas around the Tokyo Power Fukushima Daiichi Nuclear Power Plant after the accident caused by the earthquake and tsunami on March 11, 2011. Radioactive cesium pollution in agricultural ponds that supply irrigation water in this region was a concern for the restart of farming. Therefore, it is important to determine the movement characteristics of radioactive cesium around agricultural reservoirs. In this ongoing study since June 2013, we measured the concentrations of radioactive cesium in inflow, outflow, and pooled water in a small agricultural reservoir located in the Abukuma Mountains. The area of the pond was 0.37 ha, and its pondage was 7500 m³. The concentration of total radioactive cesium in the water was relatively high, around 1-3 Bq/kg, during the summer, but decreased to 0.2-1.5 Bq/kg after October. However, the concentration of total radioactive cesium of the outflow temporarily increased to 2.9-4.0 Bq/kg, when the water level decreased by 1.2 m in the middle of September. The increase in radioactivity was believed to be due to disturbance of the bottom water and sediment caused by relatively fast water flow. The dissolved radioactive cesium concentration in the inflow was 0.02-0.07 Bq/kg, whereas that in the outflow was 0.02-0.11 Bq/kg; both were considerably lower than the total radioactive cesium concentration. The ratios of dissolved radioactive cesium to total radioactive cesium were 1-5% in the inflow and 1-3% in the outflow. Thus, our results showed a positive correlation between the total radioactive cesium concentration in stored water and that in precipitation that occurred over the previous 5 days.