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<p>Nitrate contamination in groundwater poses a significant threat to drinking water safety and ecological health in rapidly urbanizing regions. Establishing the natural background levels of nitrate in groundwater is essential for effective pollution prevention and for distinguishing anthropogenic impacts from natural conditions. In this study, 166 groundwater samples and 12 isotope samples were collected from Zhuhai City, China. By integrating Cl<sup>−</sup>–NO<sub>3</sub><sup>−</sup>/Cl<sup>−</sup> ion ratio diagrams with the Grubbs method, we determined and validated the natural background levels of nitrate in groundwater. A qualitative analysis of the driving factors influencing these levels was conducted, and recommendations for groundwater nitrate pollution control were proposed. Results show that the environmental background concentrations of nitrate in the study area range from 1.51 to 57.78 mg/L. Overall, background levels in the porous aquifers of the plain areas are substantially higher than those in the fractured-bedrock aquifers of the hilly areas. In the validation analysis, anomalous samples from Unit S1 exhibit δ<sup>15</sup>N–NO<sub>3</sub><sup>−</sup> values exceeding 10‰, indicating significant sewage-derived contamination. In contrast, anomalous points in Unit S2 are concentrated in hilly areas and characterized by lower nitrate concentrations, reflecting limited human influence. The reliability of anomaly identification was confirmed through integration of land use patterns with isotopic data. Groundwater nitrate background levels are controlled by a combination of natural and anthropogenic factors. In the plains, organic-rich lacustrine-alluvial silt layers, poor hydrodynamic conditions conducive to solute accumulation, and shallow oxidizing aquifer environments collectively lead to background concentrations far exceeding drinking water standards. In the hilly areas, granite bedrock releases negligible amounts of nitrogen, resulting in inherently low background levels. These findings provide valuable insights for accurately identifying nitrate pollution in groundwater systems within rapidly urbanizing contexts, optimizing nitrogen management strategies, and safeguarding groundwater resources.</p>

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Natural background levels of nitrate in groundwater and the driving factors in rapidly urbanizing regions

  • 期刊论文

  • 发表日期：

    2026年5月21日

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  • Yuandong Deng,
  • Xueyan Ye,
  • Xinqiang Du

摘要

Nitrate contamination in groundwater poses a significant threat to drinking water safety and ecological health in rapidly urbanizing regions. Establishing the natural background levels of nitrate in groundwater is essential for effective pollution prevention and for distinguishing anthropogenic impacts from natural conditions. In this study, 166 groundwater samples and 12 isotope samples were collected from Zhuhai City, China. By integrating Cl−–NO3−/Cl− ion ratio diagrams with the Grubbs method, we determined and validated the natural background levels of nitrate in groundwater. A qualitative analysis of the driving factors influencing these levels was conducted, and recommendations for groundwater nitrate pollution control were proposed. Results show that the environmental background concentrations of nitrate in the study area range from 1.51 to 57.78 mg/L. Overall, background levels in the porous aquifers of the plain areas are substantially higher than those in the fractured-bedrock aquifers of the hilly areas. In the validation analysis, anomalous samples from Unit S1 exhibit δ15N–NO3− values exceeding 10‰, indicating significant sewage-derived contamination. In contrast, anomalous points in Unit S2 are concentrated in hilly areas and characterized by lower nitrate concentrations, reflecting limited human influence. The reliability of anomaly identification was confirmed through integration of land use patterns with isotopic data. Groundwater nitrate background levels are controlled by a combination of natural and anthropogenic factors. In the plains, organic-rich lacustrine-alluvial silt layers, poor hydrodynamic conditions conducive to solute accumulation, and shallow oxidizing aquifer environments collectively lead to background concentrations far exceeding drinking water standards. In the hilly areas, granite bedrock releases negligible amounts of nitrogen, resulting in inherently low background levels. These findings provide valuable insights for accurately identifying nitrate pollution in groundwater systems within rapidly urbanizing contexts, optimizing nitrogen management strategies, and safeguarding groundwater resources.