Groundwater pollution mechanisms in karst critical zone of western mountain of the Jinci Spring area

ObjectiveKarst groundwater resources are vital water sources in China. Due to the combined effects of global climate change and intense human activities, such as coal mining, groundwater quality in the Jinci Spring area has deteriorated. Identifying water environmental issues and understanding the groundwater pollution mechanisms in the karst critical zone of this area are crucial for the protection of karst groundwater resources. MethodsThe groundwater quality in the spring area was evaluated using the entropy weight method and water quality index. Based on the water quality assessment, isotopic tracing of sulfate oxygen and nitrate nitrogen in groundwater was further performed to trace pollution sources. Additionally, the pollution pathways in karst groundwater were identified through the analysis of inorganic carbon isotopes, strontium isotopes, and sulfur isotopes. ResultsThe results showed that the average sulfate concentration in karst groundwater was 582.07 mg/L, while the nitrate concentration in pore water reached 424.72 mg/L, indicating obvious sulfate and nitrate pollution in the groundwater from the study area. Sulfur isotopes in the polluted karst water exhibited a remarkable negative deviation, and the strontium and carbon isotopic characteristics of nitrate-polluted karst water resemble to those of deep pore water. The primary source of excessive sulfate in groundwater is sulfide oxidation and gypsum dissolution, while sewage discharge and manure input are the important sources of nitrate pollution. The main pollution pathways in karst aquifers include reverse recharge from pore water and cascade recharge from upper-layer goaf water. ConclusionThis study provides important scientific evidence for the control of karst groundwater pollution and the rational development and utilization of karst water resources in the Jinci Spring area.