Watershed-geochemical model to simulate dissolved and particulate Cs discharge from a forested catchment

Sakuma, Kazuyuki   ; Hayashi, Seiji*; Yoshimura, Kazuya  ; Kurikami, Hiroshi  ; Malins, A.  ; Funaki, Hironori ; Tsuji, Hideki*; Kobayashi, Takamaru*; Kitamura, Akihiro   ; Iijima, Kazuki  

We developed a watershed-geochemical model for simulating dissolved and particulate Cs discharges from a forest catchment in the upstream of the Ohta River. We connected a forest ecosystem compartment model to the 3-D watershed model GETFLOWS (GEneral-purpose Terrestrial Fluid-flow Simulator) to describe the dynamics of Cs between the forest ecosystem and the river system. The compartment model included sites for non-leachable and leachable Cs in the organic layer. The latter sites could model how stocks of leachable Cs increase with ambient temperature and consequently the rate of decomposition of organic matter. The simulation results for dissolved Cs concentrations in river water for the period 1 January 2014 to 31 December 2015 were in good agreement with measurements from the catchment. The simulations reproduced the dissolved Cs concentration peaks that occurred during three typhoon events and the seasonal variations under base flow conditions. The results support theories which suggest leaching from the organic layer in forests is a primary factor affecting dissolved Cs concentrations in river water under base and storm flow conditions.