Advances in researches on ammonia, nitrite and nitrate on migration and transformation in the groundwater level fluctuation zone

Ammonia, nitrite and nitrate are typical pollutants in shallow groundwater and in the vadose zone, and their migration and transformation processes are highly concerned. In recent years, new studies have focused on the three-nitrogen in the groundwater level fluctuation zone. This paper comprehensively uses the literature measurement analysis method to quantitatively analyze the related research trends, and systematically summaries the latest research results of the formation and characteristics of the groundwater level fluctuation zone, the migration and transformation process of the three-nitrogen and their biogeochemical processes in the fluctuation zone. The results show that environmental indicators such as soil moisture content, redox potential, contents of dissolved oxygen and organic matter in the groundwater level fluctuation zone have remarkable zoning rules, and the microbial community structure and functional genes are more diversified with obvious layers. As the groundwater levels fluctuate, the three-nitrogen in the vadose zone is easy to leach into the groundwater and migrate. As the groundwater levels rise, nitrification weakens, denitrification enhances, and as the groundwater levels drop, nitrification enhances, and denitrification weakens. Finally, this paper prospects the research hotspots and directions in the future: (1) the groundwater chemical evolution analysis is combined with the high-throughput sequencing method of molecular biology to explore the three-nitrogen transformation and microbial action mechanism in the groundwater level fluctuation zone. (2) In addition to nitrification and denitrification, the researches on dissimilation reduction, assimilation reduction and anaerobic ammonia oxidation processes are increased. (3) The groundwater level fluctuation process with more scenarios and influencing factors are analyzed, and the key influencing factors of the three nitrogen transformation in the groundwater level fluctuation zone are identified.