Fingerprint methods for suspended sediment transport processes by using X-ray fluorescence analysis

Suspended sediment (SS) can have significant impacts on ecological system, and high SS concentration can have significant impacts on human life. In the previous studies, radionuclide analysis has been applied to evaluate the production of SS in the river basins, which demonstrated that the surface soil erosion can be estimated by using radionuclide Pb-210ex. However, radionuclide analysis cannot indicate the relative amounts of SS transported from each individual sub-basin to the downstream end. Thus, X-ray Fluorescence Analysis (XRF Analysis) can be considered as an alternative method to radionuclide analysis because the XRF Analysis can measure 21 chemical compositions, Na₂O, MgO, Al₂O₃, SiO₂, P₂O₅, SO₃, Cl, K₂O, CaO, TiO₂, Cr₂O₃, MnO, Fe₂O₃, Co₂O₃, NiO, CuO, ZnO, Rb₂O, SrO, BaO, and Y₂O₃ by using X-ray Fluorescence Analyzer.

In June of 2007, high turbidity, which is more than 10,000 (NTU), was measured in the Oromushi River basin of Hokkaido in Japan. Therefore, this study aims to clarify the mechanism of the transport of SS in the Oromushi River basin. We measured chemical compositions of soil with diameter less than 63 μm in the Oromushi River basin in order to pay attention to SS by using XRF. The Principal Component Analysis revealed that SiO₂, Al₂O₃, Fe₂O₃, CaO and Na₂O are the dominant chemical compositions. Although the predominant composition was the same in a river basin including the downstream end, significant differences were found in the pattern of chemical compositions. Therefore, by using the chemical compositions of SiO₂, Al₂O₃, Fe₂O₃, CaO and Na₂O, the Mixing Stable Isotope Analysis in R model (MixSIAR) based on Bayesian statistics was applied to estimate the transportation rate of SS from each sub-basin to the downstream end, which agreed with the field experiment results very well. As a result, spatial patterns of SS transportation rate are found to be strongly related to surface soil type.