[H-TT15] Development and application of environmental traceability methods

[HTT15-07] Fluvial transport of suspended solids in the middle and lower reaches of the Fuji River system estimated from Sr isotopes

*Shinya Takano¹, Tomoya Iwata², Ki-Cheol Shin¹, Ichiro Tayasu¹ (1.Research Institute for Humanity and Nature, 2.Faculty of Life and Environmental Sciences, University of Yamanashi)

Keywords:Sr isotopes, suspended solids, Fuji River, turbidity, fluvial transport

The turbidity of the Fuji River has recently been increased and concerned as a major cause of the habitat degradation of aquatic organisms in the river and the adjacent ocean system, Suruga Bay. We investigated the Sr isotope ratio of river water, suspended solids (SS), and fluvial sediments in the middle and lower reaches of the Fuji River system (including the Hayakawa and the Amehata River tributary systems) to identify the source and the spatial extent of downstream transport of turbidity. Strong turbidity of the Fuji River system was observed under high-flow condition after rainfall in the basin; the SS of the Hayakawa River system showed quite high SS concentrations (approximately 500–>1000 mg L^-1). The comparison of SS concentrations between the upstream and downstream reaches of the Amehata Dam showed that sediment leakage from the Dam may less contribute the turbidity in the downstream reaches. The Sr isotope mass-balance model revealed that the contribution of riverine SS derived from the Hayakawa River system to that of the Fuji River was very high (approximately 65%, half of which was derived from the Amehata River). In contrast, the fluvial sediments in the downstream reaches of the Fuji River contained only 11% of component derived from the Hayakawa River system. These results suggest that the riverine SS derived from the Hayakawa River system is a major source of the turbidity in the Fuji River, and most of SS is transported into the Suruga Bay without being accumulated in riverbed sediments.