Factors influencing the variation of 137Cs activity concentration in two rivers within the difficult-to-return zone, Fukushima

This study investigated the relationship between 137Cs activity concentration and water quality to clarify the factors affecting variation of 137Cs activity concentration in the waters of Maeda and Saruta Rivers within the Difficult-to-Return Zone after the Fukushima Dai-ichi Nuclear Power Stations accident. In addition, the factors influencing the variation of apparent distribution coefficient between water and sediment were examined. The variation in dissolved 137Cs activity concentration was caused by decomposition of dissolved organic carbon in the Maeda River and the ion exchange reactions with K+ and Na+ in the Saruta River, respectively.