Geochemistry of the upper Han River basin, China, 1: Spatial distribution of major ion compositions and their controlling factors

The upper Han River basin (approximately 95,200 km2) is the water source area of China's South-to-North Water Transfer Project. Over the period from 2005 to 2006, a total of 292 grab samples collected from 47 sites in the upper Han River were analyzed for major ions (Cl−, NO3-, SO42-, HCO3-, Na+, K+, Ca2+ and Mg2+), Si, T, pH, EC and TDS. Correlation matrix and principal component analysis were used to quantify the geochemical and anthropogenic processes and identify factors influencing the ionic concentrations. The results reveal that the waters are slightly alkaline with low ionic strength, and all ions show remarkable spatial variations. The lowest solute concentrations are observed in catchment with higher vegetation cover, with higher Cl−, NO3- and SO42- concentrations occur in catchments with industrial establishments. The major ion chemistry of the upper Han River basin is mainly controlled by rock weathering with HCO3- and Ca2− dominating the major ion composition. The spatial variation in overall water quality as well as comparison with WHO and Chinese standards for drinking water indicates that the basin has high-water quality, yet it is possible that NO3- enrichment will occur in the near future. This research will help water conservation in the basin for the interbasin water transfer project.