[Chemical Characteristics and Causes of Groups Water in Niangziguan Spring]

Discharge in Niangziguan Spring is 7.19 m³·s^-1, which is the main water supply source for Yangquan City and Pingding County. Every year, Yangquan municipal government take water from the mouth of Niangziguan Spring to supply drinking water to urban residents at a rate of approximately 1.7 m³·s^-1. It is of great significance to determine the characteristics and causes of variations in spring water flow conditions for the appropriate utilization of water resources and pollution prevention. Here, sample collection and hydrochemical isotope analyses were undertaken for the Niangziguan Spring area to chemically characterize the water environment and genesis. The pH of the karst spring is 7.2-7.5 with an average of 7.36; the calcium content of the water is 112.1-135.2 mg·L^-1 with a mean value of 131.4 mg·L^-1; the concentration of magnesium ions is 34.8-42.3 mg·L^-1 with an average of 40.8 mg·L^-1; the concentration of K⁺+Na^- ions is 41.6-46.7 mg·L^-1 with an average of 45.2 mg·L^-1; and the sulfate ion concentration is 185.6-271.8 mg·L^-1 with a mean value of 255.4 mg·L^-1. The hydrochemical type of the aquifer is classified as HCO₃·SO₄-Ca·Mg. The spring water is characterized by high Ca²⁺, Mg²⁺, and SO₄^2- concentrations, and low Na⁺, K⁺, and Cl^- concentrations. The supply path of Chengxi Spring is shortest followed by Wulong Spring. The supply paths of the remaining five spring are much longer. The Niangziguan Spring water environment is characterized by increasing pollution from coal mine acid drainage alongside decreasing inputs from domestic sewage. Environmental isotope tracing shows that sulfate in Chengxi Spring mainly derives from precipitation and gypsum dissolution, and the concentrations of sulfate in Wulong Spring are increasing. These changes are mainly driven by the amount of coal mine acid water pollution in the area.