Factors affecting 137 Cs concentrations in river water under base-flow conditions near the Fukushima Dai-ichi Nuclear Power Plant

To confirm factors affecting 137Cs concentration in river water after the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, this study conducted monthly observations of nine rivers near the FDNPP from April 2017 to March 2018 under base-flow conditions. The annual mean dissolved and particulate 137Cs concentrations correlated well with the mean 137Cs deposition in the catchment. The normalized 137Cs concentrations in both phases by dividing by the mean 137Cs deposition in the catchment showed significant negative correlations with the 137Cs deposition ratio for forests. The inflow from the downstream plain areas increased the 137Cs concentrations near the FDNPP.