Hydrogeochemical Characteristics and Quality Assessment of Groundwater in an Irrigated Region, Northwest China

Groundwater is one of the most important sources of water for drinking and irrigation in arid and semi-arid regions of the world. In this study, 50 groundwater samples were collected and analyzed for various chemical constituents (pH, TDS, Na+, K+, Ca2+, Mg2+, SO42-, Cl-, HCO3-, NO3-, and F-) to identify the hydrogeochemical characteristics, and to evaluate its suitability for drinking and irrigation uses in Zhongning area of Northwest China. Results showed that groundwater was slightly alkaline in nature. Fluoride and nitrate concentrations in the groundwater of the study region were much higher than its prescribed limits for drinking purposes. A factor analysis (FA) was implemented to understand the contamination source of groundwater in the region, and the results indicated that rock-water interaction, geogenic, and human-induced contamination were the major factors influencing groundwater chemistry. An entropy-weighted water quality index (EWQI) was employed to evaluate the water quality for drinking purpose. Mg2+, Ca2+, SO42-, HCO3-, and TDS played the leading roles in influencing the groundwater quality with high weights. Forty-eight percent of groundwater samples were unfit for drinking purpose in the study area, due to poor quality. Elevated concentrations of SO42-, Cl- and NO3--N in groundwater caused poor quality and extremely poor quality water, which may be attributed to human activities. According to the calculation of sodium percentage (Na%), sodium adsorption ration (SAR), and permeability index (PI), the majority of the groundwater samples were suitable for irrigation. However, it should be noted that 26% of the samples were unfit for irrigation because of the high salinity in the groundwater. This is mainly attributed to the intense evaporation and the intensified irrigation activities in the region. The findings in this study contribute to a better understanding of groundwater sustainability for supporting water management and protection in the future.