Deposition records in lake sediments in western Japan of radioactive Cs from the Fukushima Dai-ichi nuclear power plant accident

• We studied lake deposition records of radioactive Cs from Fukushima Dai-ichi NPP.
• Sediment trap observations were performed before and after the FDNPP accident.
• Precipitation and geomorphology of the catchment influence Cs discharge.
• The contribution of FDNPP to the lake sediment decreased within a few months.
• The major transport processes of FDNPP radioactive Cs to the lake have changed.

Sediment trap observations of lakes in western Japan before and after Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident indicate that changes in the radioactive Cs discharge are influenced by fluctuations in precipitation and geomorphological conditions in each catchment. Contributions of FDNPP-derived 134,137Cs to the sediment decreased from 19–48% to 10–15% within a few months, implying that the major transport processes of FDNPP-derived 134,137Cs have changed from direct fallout to transport by soil particles.