[Major ionic features and their sources in the Nam Co Basin over the Tibetan Plateau].

A preliminary study of major ions in water of three rivers (Niyaqu, Qugaqie, Angqu) in the Nam Co Basin has been carried out in June-October 2006. An obvious difference is found among these rivers, whose ionic characteristics are mainly influenced by the length of rivers and their supply sources. Among the three rivers, the contents of total dissolve solids (TDS) is 79.48 mg/L, 23.44 mg/L, and 111 mg/L in the Niyaqu, Qugaqie, and Angqu, respectively. The hydro-chemical type is CCa for the Qugaqie, between CNa and CCa for the Angqu, and between the Angqu and Qugaqie for the Qugaqie. Changes in ionic concentrations are also related with discharges of the rivers. According to principal component analysis and correlation analysis, the main chemical contents derive from Ca2+ and HCO3(-) in carbonate for the Niyaqu, glacier meltwater and carbonate for the Qugaqie, and Na+, Mg2+ and Cl(-) in evaporates for the Angqu.