[Characteristics and Causes of Groundwater Salinization in the Plain Area of the Lower Kashgar River]

This study revealed the distribution characteristics and formation mechanism of groundwater salinization in the plain area of the lower Kashgar River in Xinjiang, which can provide scientific basis for a local sustainable groundwater exploitation plan and practical significance for local water supply security and social stability. Fifteen phreatic water samples, 38 shallow confined groundwater samples, and 16 deep confined groundwater samples were collected in September 2018. Mathematical statistics, a Duorv diagram, PCA-APCS-MLR model, ion ratios, and hydrogeochemical simulations were comprehensively used for sample analysis. The results showed that groundwater was weakly alkaline in general (pH ranged between 6.48 and 8.60 with an average of 7.57), with total dissolved solids (TDS) ranging from 573.0 to 16700.0 mg·L^-1. Groundwater was mainly composed of Cl^-, SO₄^2-, Na⁺, and Ca²⁺. The main groundwater hydrochemical types included were HCO₃·SO₄·Cl, SO₄, and SO₄·Cl. No brine was observed in the study area, phreatic water was mainly composed of brackish water and saline water, and confined groundwater was mainly composed of saline water. The salinization coefficient calculation results showed that the salinization degree gradually increased from phreatic water to deep confined groundwater. Evaporation concentration and lixiviation were the main factors leading to the salinization of groundwater. The dissolution and cation exchange of carbonate and silicate rocks gradually weakened from phreatic water to deep confined groundwater, whereas the dissolution of evaporite rock always dominated and was gradually strengthened, which was also the primary factor that caused the salinity of deep groundwater to be higher than that of shallow groundwater. Human activities such as agricultural fertilization, unreasonable use of surface water for irrigation, and improper treatment of domestic sewage had a certain impact on groundwater salinization. The leaking recharge of salt water from adjacent aquifers aggravated the groundwater salinization.