Review on the distribution and influencing factors of nitrate and ammonia in regional groundwater: current status, differences and analytic techniques
摘要
Excessive concentrations of nitrate (NO3-N) and ammonia (NH4-N) in groundwater have become a global water quality issue. Despite widespread research on NO3-N and NH4-N exceedances in groundwater, systematic comparisons of their pollution characteristics remain limited. This review examines the spatial distribution, controlling factors, and source identification techniques of NO3-N and NH4-N in regional groundwater, with an emphasis on comparing their differences. The results indicated that NO3-N contamination is prevalent in regional groundwater, with an average exceedance rate of 15%, evolving spatially from localized to widespread patterns. Due to its high mobility, NO3-N primarily accumulates in groundwater at depths of 50–150 m, with the exceedance rate reach up to 58.3%. In contrast, NH4-N exhibits limited distribution and lower diffusion capacity, primarily accumulating in shallow groundwater or soil layers, with the highest exceedance rate observed at approximately 25 m depth. These distributional differences are mainly controlled by four factors, including pollutant load, hydrogeological conditions, biogeochemical processes, and sedimentary environments, which collectively determine the distinct characteristics of NO3-N and NH4-N pollution. Numerous techniques are available for identifying influencing mechanisms, with numerical modeling and machine learning as the most widely adopted due to their efficiency and accuracy compared to traditional methods. These advanced approaches are frequently integrated with conventional techniques to enhance result reliability. The findings of this study effectively elucidate the distinct characteristics and behavioral differences of NO3-N and NH4-N pollution in regional groundwater, offering critical information for evidence-based water resource management decisions.