Geochemistry of the upper Han River basin, China. 2: Seasonal variations in major ion compositions and contribution of precipitation chemistry to the dissolved load.

A total of 252 water samples were collected from 42 sites across the upper Han River basin during the time period from 2005-2006. Major ions (Cl(-), NO3(-), SO4(2-), HCO3(-), Na+, K+, Ca2+ and Mg2+), Si, water temperature, pH, EC and TDS were determined and consequently correlation matrix, analysis of variance, factor analysis and principal component analysis were performed in order to identify their seasonal variations and atmospheric inputs into river solutes. The results reveal that pH, EC, TDS, Cl(-), SO4(2-), HCO3(-), Ca2+ and Mg2+, K+ and Si generally tend to show the minimum compositions in months belong to the rainy season, while the dry season for NO3(-) and Na+. NO3(-), Mg2+ and Si have the maximum concentrations in months belong to the rainy season. By comparing the major ions relating to hydrological regime, NO3(-), contrary to other elements, has higher concentration in the rainy season. The overall water quality is non-polluted, while there are indications of enrichment of inorganic anions including NO3(-) causing water entrophication in the near future. The atmospheric inputs contribute to river solutes is limited with a mean inputs of approximate 1% in the basin. The understanding of the major ion dynamics would help water quality conservation in the basin for China's interbasin water transfer project.