Strontium isotope analysis identifies the source and transport of fluvial suspended solids in the Fuji River Basin, Japan

Abstract

Study region: The middle and lower reaches of the Fuji River system, Central Japan Study focus: The increase in turbidity over the last decade is considered a major cause of habitat degradation of aquatic organisms in the Fuji River and the adjacent coastal area of Suruga Bay. This study identifies the source and fate of suspended solids (SS) in the Fuji River system based on an investigation of the isotopic composition of strontium (87Sr/86Sr) in river water, SS, and fluvial sediments. New hydrological insights for the region: The Sr isotope mass-balance model revealed that the strong turbidity (SS > 500 mg L−1) observed in a major tributary system—the Hayakawa River—accounted for 65 % of riverine SS in the Fuji River; however, the Hayakawa River water contributed only 24 % to the total river water flow in the Fuji River. In contrast, riverbed sediments in the Fuji River contained only 11 % of the sediments derived from the Hayakawa River system. These results suggest that the Hayakawa River SS could be a major source of turbidity in the Fuji River but most of it flowing into Suruga Bay without significant sedimentation. The present Sr isotope ratio, depends on host rock types in geologically heterogeneous catchments, can be used for fingerprinting of fluvial SS and improving ecosystem management planning in watersheds susceptible to frequent soil erosion and landslides.

Keywords

• Sr isotopic composition
• Riverine SS
• Soil erosion
• Turbidity
• River water
• Fluvial sediments