[A-HW22] Hydrological Cycle and Water Environment

[AHW22-11] Transport processes of earth surface materials and atmospheric radionuclides in reservoir-catchment system

*Shinya Ochiai¹, Seiya Nagao¹, Yoshiki Miyata^1,2, Atsushi Matsuki¹ (1.Institute of Nature and Environmental Technology, Kanazawa University, 2.Organization of Frontier Science and Innovation, Kanazawa University)

Keywords:atmospheric radionuclides, earth surface materials, transport processes, reservoir-catchment system

To investigate the transport processes of earth surface materials in reservoir-catchment system, temporal changes in deposition fluxes of atmospheric radionuclides (²¹⁰Pb and ⁷Be) and their sedimentation fluxes in the irrigation reservoir were observed in Noto Peninsula. Atmospheric deposition fluxes of ²¹⁰Pb and ⁷Be were observed during one month with a collecting pan installed in Noto Atmospheric Monitoring Observatory in Suzu City during June 2016 to September 2017. Sedimentation fluxes of ²¹⁰Pb and ⁷Be were also observed with sediment trap installed in the Shin-ike reservoir located at the 5 km from the atmospheric monitoring site for same intervals of atmospheric deposition.Deposition fluxes of atmospheric ²¹⁰Pb and ⁷Be ranged 0.5-5.5 Bq/m/day and 3.1-25 Bq/m/day, respectively, and showed clear seasonal fluctuation with high deposition flux during winter and low during summer. Sedimentation flux of ²¹⁰Pb to the reservoir bottom was much larger than ²¹⁰Pb deposition flux from the atmosphere, suggesting that ²¹⁰Pb eroded from the catchment was major source to reservoir sediment. On the other hand, sedimentation flux of ⁷Be was almost same level with deposition flux from the atmosphere, suggesting that the contribution of the catchment-derived ⁷Be is negligible. These differences in contributions of catchment-derived radionuclides to reservoir sediment may be associated with the half-lives of ²¹⁰Pb (22.3 years) and ⁷Be (53 days) and the residence time in the catchment area.