Chemical characteristics, formation mechanism and exploiting suggestions of surface water and shallow groundwater in the Maqinqu River Basin, Ritu County, Xizang

Objective In order to clarify the chemical characteristics of surface water and shallow groundwater and their controlling factors in the Maqinqu River Basin, Ritu County, Ngari Prefecture, Xizang,

Methods a total of 22 surface river water, lake water and well water samples were systematically collected in July 2021 and July 2022 in the Maqinqu River Basin. The hydrochemical characteristics of surface water and shallow groundwater and their controlling factors in the Maqinqu River Basin were comprehensively analyzed by applying mathematical statistics, WQI water quality evaluation, Piper's trilinear diagram, Gibbs' diagram, and ionic scale factor method.

Results The results showed that the pH value of surface river water and shallow groundwater bodies in the Maqinqu River Basin was 7.4~8.4, which was weakly alkaline, and the water quality types of the other water bodies were Class I except for the Spanguer water body, which was Class Ⅲ, and the water quality of the water bodies in the area was excellent. The chemical type of surface river water and shallow groundwater is HCO₃−Ca type, the water chemistry type of shaerda Lake water is HCO₃−Mg−Ca type, and the water chemistry type of Spanguer Lake water is Cl·HCO₃−SO₄−Na−K type, and the relationship between the stable isotope composition of hydroxide and oxygen indicates that the glacial meltwater is an important recharge source of the surface river water and shallow groundwater in the Maqinqu River Basin, where the glacial meltwater, surface river water and atmospheric precipitation to shallow groundwater is 38.5%, 24.4% and 37.1%, respectively.

Conclusions The main chemical composition of shallow groundwater and surface river water in the Maqinqu River Basin is controlled by the weathering and dissolution of saline and silicate rocks. The ionic composition of the water in Spanguer lake is controlled by evaporation and crystallization. Some of the shallow groundwater and surface river water is enriched in Na⁺ relative to Cl⁻, and surface river water is poor in Ca²⁺ and Mg²⁺ relative to HCO₃⁻, which is mainly controlled by cation exchange. The quality of shallow groundwater in the area is excellent, which can be used for the living of the local people by digging shallow wells. The maximum daily water flow of the spring point of Spanguer Lake can be used for the living water of about 5000 people. We should pay attention to strengthening the ecological protection of surface water in the area.