Sediment transport processes in a reservoir–catchment system inferred from sediment trap observations and fallout radionuclides

Sediment transport processes and their responses to hydrological conditions were investigated based on sediment trap observations in a reservoir–catchment system in Japan. The annual discharge rate of 134Cs from the catchment was much higher than that of 137Cs. This difference suggests that 134Cs freshly derived from the Fukushima Dai-ichi Nuclear Power Plant accident accumulated in the surface soil, which acted as a major sediment source. The seasonal changes in the 137Cs/210Pbex ratio in the trap samples corresponded well to the precipitation changes. This suggests that the precipitation intensity affects the source of eroded sediment in the catchment.