Study on nitrogen pollution types and isotopic tracing of urban water bodies

The emission of various nitrogen-containing pollutants in cities causes various hazards in the environment. Clarifying the source and circulation law of nitrogen pollution can provide a series of supports for environmental governance. In this paper, not only the mechanism and harm of nitrogen pollution but also the status and types of nitrogen pollution in urban water environment were described. The latest progress in the research on the traceability of nitrogen pollution in urban water was reviewed. The surface waters were mainly affected by total nitrogen, nitrate nitrogen, and ammonia nitrogen pollutions. Most of the water environment only met the class Ⅳ-Ⅴ water quality standards, and human activities were the main contributor to the nitrogen pollution in urban water environment. In addition, the source tracing technology of nitrogen pollution in water （hydrochemistry analysis, isotope tracing, microbial source tracing, isotope source analytical model, etc.） and the characteristic values of nitrate-nitrogen and oxygen isotopes in end-member substances were further summarized, which provided a reliable way to trace the source of nitrogen pollution and clarify the migration law of nitrogen pollution. This review is of great significance for the traceability and prevention of nitrogen pollution in urban water environment.