Analysis of Water Chemistry Characteristics and Main Ion Controlling Factors of Lakes in the Nagqu Area of the Qinghai–Tibet Plateau in Summer

Abstract

The Nagqu area is in the northern part of the Qinghai–Tibet Plateau, and its average altitude is above 4000 m. Due to the area’s high altitude, there is relatively little information about its lakes. Therefore, to supplement the basic information of lakes in the area, this study collected surface water samples from 12 lakes, including Gangtang Co, Pusaier Co, Guojialin Co, Dagze Co, Yangnapeng Co, Bankog Co, Dangqung Co, Chaxiabu Co, Angdar Co, Bengze Co, Guogen Co, and Yibug Caka from July to August 2020. Furthermore, the factors controlling the lake water chemistry characteristics and the main ion sources were explored using the Piper, Gibbs, and ion ratio methods. The results were as follows: (1) The lakes had high levels of salt, alkalinity, and mineralization, and all the lakes except Bengze Co were salt lakes. The 12 lakes met the Class V water standard. (2) Dangqung Co, Bankog Co, Guojialin Co, Daze Co, and Yangnapeng Co were in the initial stage of lake succession, while the others were in the later stages of lake succession. (3) Evaporation–crystallization was the most important factor controlling the water chemistry of the 12 lakes, and most of the ions in the lakes come from the dissolution of evaporite.