Identifying the provenance of bottom sediments in the Three Gorges Reservoir using stable Pb isotopes

Abstract Sediment deposition is considered a potential risk to the operation of the Three Gorges Reservoir (TGR). In this study, the bottom sediments of the TGR and its main tributaries were sampled during the flood, dry, and even periods, for 2017–2018, together with the surrounding hillslope soils. These samples were analyzed for Pb isotopes, and major and trace elements. Through the Pb isotopic comparison, it was understood that the TGR sediments originated from the weathering of rocks in the Qiangtang, Songpan–Ganzi, and Regional Yangtze tectonic blocks. Combined with the hydrological data, the TGR sediments were isotopically determined to be primarily fed by upstream input, the hillslope soil erosion, and the catchment weathering of regional tributaries. The geochemical data were in agreement with the results of the Pb isotope analyses. Using the IsoSource model, proportional contributions from distal (e.g., Jinshajiang), regional (surrounding tributaries), and proximal (hillslope soils) sources were calculated to be 50%, 20%, and 30%, respectively, in the flood period, 40%, 30%, and 30%, respectively, in the dry period, and 40%, 25%, and 35%, respectively, in the even period. Thus, the considerable input of hillslope and tributary erosion in recent years should be of concern. This study provides deep insight into the provenance of the bottom sediments in the TGR and will help prevent excessive sediment deposition in this reservoir.