Hydro-geochemistry and genesis of major ions in the Yangtze River, China

Based on the data of 76 water samples of the Yangtze River (36 of them located in the main stream and 40 of them in major tributaries and anabranches), the effect of lithology and main weathering process of the river water have been studied by means of statistical approaches such as Gibbs figure, Triangle plot and principal component analysis (PCA). The results show that the geochemistry of major ions in the Yangtze River are mainly controlled by rock weathering. Among them, carbonates and evaporates account for 43.6% and 37.9% of total ion equivalent concentration for the main stream, while the contribution for tributaries are 33.1% and 39.1%, respectively. The primary weathering process in the main stream of the Yangtze River is the solution of dolomite and calcite. The ratio of Cl-/(Na++K+) in the main stream is close to 1∶1, reflecting the significance of evaporite weathering. The lower Si/K ratio indicates that the weathering reactions took place in superficial environment and its products are cation-rich secondary minerals.