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Abstract
The concentration of dissolved ions, including K+, Na+, Ca2+, Mg2+, Cl−, SO4 2−, HCO3 −, CO3 2−, is an important index for river water quality. By employing the data of measured ions in the Weihe River basin, relationships between the concentration of ions and water discharge and sediment loads are revealed. Generally one of the most important factors affecting the concentration of ions is water dilution, which results in a continuous reduction in the concentration of ions following increasing flow discharge. In a dry season, the concentration of ions decreases with water discharge and sediment concentration; whereas in a wet season, however, the relationships are more complex because the soil erosion can be extremely intensive and sources of ions are rather diverse. Lithology and climate are the two most important influencing factors for these relationships. The Jinghe River and Bahe River are two typical tributaries of the Weihe River. The Jinghe River is from the Loess Plateau and carries extremely high sediment loads, and the Bahe River is from the south rocky mountains and carries a low sediment load. Since there are a multitude of sources of ions and influencing factors in the Jinghe River basin, compared with the Bahe River, the concentration of ions is higher, and relationships between the concentration of ions and water discharge and sediment concentration are much more diverse. The large‐scale soil and water conservation strategies performed in the late 1960s have reduced the water and sediment yield from the basin, which have changed the relationships between the concentration of ions and water and sediment. Hyperconcentrated floods happen less and surface erosion becomes the major resource of ions, consequently the relationships between the concentration of ions and sediment and water are more regular. This paper also reveals that if the sediment concentration is higher than a critical value, then the concentration of ions increases greatly, because of intensive soil erosion and especially hyperconcentrated floods, introducing a deeper soil and higher ions into the river system.