The evolution of hydrochemistry at a cold alpine basin in the Qilian Mountains

Investigation on water chemistry would provide the crucial information to the hydrological study. Hydrochemical analyses of precipitation, river water, well water, and spring water have been made in this study based on 62 samples from Babao river basin, China. The results indicated that the evaporation and dissolution of rocks and soil are the primary factors on the variation of ionic composition. Precipitation is of the SO4 2−Ca2+ type, whereas the main stream, tributaries, wells, and springs are of the SO4 2−Mg2+-Ca2+ type, confirming the chemical composition primarily determined by terrigenous material. All ions except NO3 − appear to represent contributions of natural sources, with most of the Ca2+ and SO4 2− coming from the soil and Na+ exhibiting a clear marine origin. Specifically, the water chemistry of underground water is influenced mainly by the weathering and dissolution of dolomite and sulfate minerals, while the main stream water may be dominated by the dissolution of calcite and dolomite. In addition, the dissolution of rock salt and silicate minerals has some contributions. These characteristics displayed that regional runoff is dominated by precipitation in summer and autumn, while it is sourced from underground water in winter and spring.