Abstract
Nitrate pollution in surface water has become an environmental problem of global concern. The effective way for controlling the nitrate pollution of surface water is to identify the pollution source and reduce the input of nitrate. In recent decades, nitrogen (δ15N) and oxygen (δ18O) isotopes of nitrate has been used as an effective approach for identifying the source and fate of nitrate pollution in surface water. However, owing to the complexity of nitrate pollution source and the influence of isotopic fractionation, the application of this method has some limitations. In this work, we systematically discussed the fundamental principle of using nitrogen and oxygen isotopes to trace the nitrate source, the fate identification of nitrate, and the major testing techniques. Subsequently, the applications of nitrogen and oxygen isotopes for source identification of surface water were illustrated. However, there are still significant gaps in the application of the source identification and transformation mechanisms to nitrate and many research questions on these topics need to be addressed.
Highlights
Growing nitrate pollution has become a common environmental problem worldwide [1].Rivers are important channels which connect the nitrogen pools of mainland and ocean.The ever-increasing nutrient substances in rivers are the key changing factors of the global water quality and biodiversity
The results of researches conducted on nitrogen and oxygen isotopes technique and geochemical methods show that the high-concentration of nitrate in farmland wastewater and in rivers is directly correlated with the use of massive chemical fertilizers [4,48]
Hydrogeology, other isotopes, and mathematical models, the δ15 N and δ18 O of nitrate are able to solve such problems as the partial overlapping of isotopic composition of various sources and isotopic composition reduced by isotopic fractionation
Summary
Growing nitrate pollution has become a common environmental problem worldwide [1]. Rivers are important channels which connect the nitrogen pools of mainland and ocean. It is of significance to identify the sources of nitrate, and analyze the nitrate transformation mechanism for water environmental protection. The human activity, hydrologic process, and migration and transformation mechanisms of nitrate vary within different land uses [6]. The major source of nitrate pollution is generally determined by the geographic position, scale, land-use type, and hydrological conditions of the watershed. Because the nitrogen isotopic compositions of nitrate and the fractionation mechanisms of nitrogenous substances are different, the value of δ15 N has been used to identify nitrate. There is no review that systematically summarizes present limitations and future prospects of application of nitrogen and oxygen isotopes. The application cases of stable isotope technique under different land-use types and basin conditions were summarized. 2. Fundamental Principle of Using Nitrogen and Oxygen Stable Isotopes to Identify the Pollution
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