2022 年 78 巻 2 号 p. I_919-I_924
Suspended Sediment (SS) in rivers negatively affects water quality, leading to increase in the costs of water treatment, loss of reservoir storage capacity and a decrease in fishery and crop productivity. In order to reduce the amount of SS in the river, it is essential to understand the mechanisms involved in sediment transport and the source of the SS in the river catchment area. Oromushi river basin in Hokkaido, which is predominantly characterized by high amounts of SS, was used as the case study. The basin was divided into 13 land groups with 18 sampling stations. The geochemical composition (Na2O, SiO2, Al2O3, CaO, Fe2O, MgO, P2O5, K2O and TiO2) of the soil samples collected from each land group and the deposited sediment at the downstream end was determined by XRF analysis. The detected geochemical components from each land group were analyzed using Structural Equation Modelling (SEM). The results suggested that most of the SS in the river originated from the agricultural field. It is mainly because the vegetation cover is cleared to create land for sowing crops, consequently exposing the soil surface to the effects of raindrop splash. Moreover, our data suggested that SEM analysis gives more reliable data than other methods.
