| To seek the geological tracers of environmental radionuclide for fingerprinting suspended sediment sources、 the surface (c. top 5 cm) soil samples were collected from stream bank in 13 subcatchments、 where the geology was categorized by era (4 types) and period (8 types) in the Mukawa River and Sarugawa River watersheds in Hokkaido、 northern Japan. Gamma ray spectrometry was conducted to determine the activities of environmental radionuclides associated with each soil samples using HP Ge well-type detector. Gamma ray spectrometry could determine 15 environmental radionuclides、 including U-series、 Th-series、 cesium-137 and potassium-40. Lead-210 excess was also determined by subtracting the activities of Pb-214 from that of Pb-210. The Kruskal-Wallis H test was conducted to assess the ability of each tracer property to discriminate between surface soil samples from the categories divided by subcatchment、 geological era and period、 suggesting that more than 11 tracer properties were available. Subsequently、 the stepwise discriminant function analysis was conducted to identify which combination of tracer properties provides the best composite fingerprint for differentiating source materials on the basis of subcatchment and geology (era and period) source groups. This analysis suggested that the composite fingerprints of more than 4 tracer properties can classify the source groups correctly with 75% to 95%. Principal component analysis showed that Pb-212、 organic matter content and K-40 were important tracer properties to discriminate source groups in this study area. These results indicate that the environmental radionuclides determined by gamma ray spectrometry can be used as fingerprint to estimate the contribution of geological source groups. |
