Hydrogeochemical genesis mechanism and secondary environmental challenges of groundwater in southern Jingyang, Shaanxi Province

Objective The southern Jingyang, Shaanxi Province is a typical loess distribution area, population gathering area, agricultural activity intensive area, and geological disaster prone area. Thus, studying the hydrogeochemical genesis mechanism and secondary environmental challenges of groundwater in this area is of great significance for the development and utilization of groundwater resources, water safety guarantee, and ecological geological environment protection on the Chinese Loess Plateau.

Methods Based on groundwater investigation, water sample collection and analysis in the area, the main ion distribution characteristics of groundwater were identified; the hydrogeochemical genesis mechanism and its main controlling factors of groundwater were revealed by the comprehensive application of hydrochemical methods and isotope theory; the suitability of groundwater for drinking and irrigation was evaluated, and its secondary environmental challenges were explained, using the integrated−weight water quality index, magnesium hazard, soluble sodium percentage, Wilcox plot, and irrigation coefficient.

Results The groundwater in this area was weakly alkaline as a whole. The TDS range of groundwater in the south bank of Jing River was 752~2108 mg/L, belonging to freshwater and brackish water, while the TDS ranged from 1232 to 3768 mg/L and was classified as brackish to saline water in the north bank. The dominant cations in groundwater were Na⁺ and Mg²⁺, and the dominant anions were HCO₃⁻ and SO₄²⁻; The hydrochemical types were mainly HCO₃·SO₄−Na·Mg and HCO₃·SO₄·Cl−Na·Mg, and the hydrochemical types in the north bank were more complex. The hydrochemical characteristics of groundwater were mainly controlled by rock weathering, among which the weathering and dissolution of silicate rocks were dominant. Meanwhile, the evaporation and cation alternating adsorption promoted the salinization of groundwater. The groundwater in the south bank was significantly affected by agricultural activities, while the groundwater in the north bank was influenced by a combination of industrial activities, domestic sewage, and human and animal manure. The drinking water quality level was mainly moderate, and the primary factors causing health risks were total hardness, NO₃⁻, F⁻, and SO₄²⁻. Most groundwater was not suitable for direct irrigation and measures should be taken to prevent salt accumulation, otherwise soil salinization may occur.

Conclusions The hydrochemical characteristics of groundwater along the banks of Jing River in the south of Jingyang, Shaanxi Province, are mainly controlled by the weathering of silicate rocks, superimposed evaporation and concentration and the influence of human activities. There are health risk factors of groundwater such as total hardness, nitrate, fluoride exceeding the standard, and the salinization of groundwater is easy to induce soil salinization. It is suggested to carry out targeted prevention and control of groundwater pollution to avoid facing more severe secondary environmental challenges.