Geochemical constraints on seasonal recharge of water and major dissolved solutes in the Huangshui River, China

The Huangshui River, an important tributary in the upper reaches of the Yellow River, has been regarded as a mother river which gestates Qinghai civilization in China. This paper presents the results of hydrogen and oxygen isotopic and water chemical analyses for the summer and winter Huangshui River water to study its seasonal recharge and major dissolved solutes. Characteristics of hydrogen and oxygen isotopes suggest that precipitation in the Qilian Mountains is the original recharge of the Huangshui River. However, in winter, the basic flow of the Huangshui River only depends on spring recharge and spring water originates from melt and infiltration of bottom layer glaciers. In summer, besides spring water, much rainfall directly recharges the Huangshui River, thus making its flux increase greatly. Water chemistry shows that the processes affecting dissolved solutes in the Huangshui River are also different between summer and winter. In summer, major ions in the river water are dominantly derived from carbonate and evaporate dissolution and anthropogenic inputs. In winter, carbonate dissolution decreases greatly while anthropogenic inputs play a much more important role for dissolved solutes in the river. Hence, further measures should be taken to lay stress on the winter Huangshui River water in order to protect the environment of the Huangshui River and reduce effects of dissolved solutes on, or prevent their pollution toward the upper Yellow River. Moreover, some measures also need to be introduced to prevent the possibility of water eutrophication caused by agricultural activities or stock raising in summer.