A stable isotope approach and its application for identifying nitrate source and transformation process in water

Abstract

Nitrate contamination of water is a worldwide environmental problem. Recent studies have demonstrated that the nitrogen (N) and oxygen (O) isotopes of nitrate (NO3(-)) can be used to trace nitrogen dynamics including identifying nitrate sources and nitrogen transformation processes. This paper analyzes the current state of identifying nitrate sources and nitrogen transformation processes using N and O isotopes of nitrate. With regard to nitrate sources, δ(15)N-NO3(-) and δ(18)O-NO3(-) values typically vary between sources, allowing the sources to be isotopically fingerprinted. δ(15)N-NO3(-) is often effective at tracing NO(-)3 sources from areas with different land use. δ(18)O-NO3(-) is more useful to identify NO3(-) from atmospheric sources. Isotopic data can be combined with statistical mixing models to quantify the relative contributions of NO3(-) from multiple delineated sources. With regard to N transformation processes, N and O isotopes of nitrate can be used to decipher the degree of nitrogen transformation by such processes as nitrification, assimilation, and denitrification. In some cases, however, isotopic fractionation may alter the isotopic fingerprint associated with the delineated NO3(-) source(s). This problem may be addressed by combining the N and O isotopic data with other types of, including the concentration of selected conservative elements, e.g., chloride (Cl(-)), boron isotope (δ(11)B), and sulfur isotope (δ(35)S) data. Future studies should focus on improving stable isotope mixing models and furthering our understanding of isotopic fractionation by conducting laboratory and field experiments in different environments.

Variation in nitrate isotopic signatures in sewage for source apportionment with urbanization: a case study in Beijing, China

“…It should be noted that there were different patterns of NO 3 − isotopic characteristics in sewage processed by WWTP or not. -H 2 O enrichment in aerobic condition since oxygen isotope fractionation was complex during nitrification (Xu et al 2016). In China, the treatment of sewage with higher TN concentrations (>30 mg/L) would usually cause the incomplete denitrification in A 2 /O technological process (Jiang et al 2014), and the average TN concentrations of raw sewage samples in this study were all above 30 mg/L across the months.…”

“…1 Site map of the study area. were significantly related to the amount of runoff from impervious areas in urban watersheds (Xu et al 2016). Normally, NO 3 − produced during subsequent nitrification was reported to contain two thirds of the δ…”

“…For example, the temperature would significantly affect the isotopic fractionation by microbial nitrification and denitrification during sewage treatment processes. To our knowledge, the δ can be advantageous to sample and analyze them (Nestler et al 2011;Xu et al 2016). Our δ 15 N and δ…”

“…Sources of N pollution in urban surface and groundwater should be identified before an efficient remediation measure is devised (Xu et al 2016), and sewage is supported as the typical urban N source (Yue et al 2010;Xue et al 2012;Ren et al 2014;Zhang et al 2015b). Nitrate (NO 3 − ) is the main form of N embedded in the discharged effluents in Chinese cities.…”

“…As with the stable isotope analysis in R language (SIAR) model, which was supposed to produce more precise results about NO 3 − source contributions, its outputs could be further improved by using more narrow ranges of NO 3 − sources provided by original source material (Xue et al 2012). Ding et al (2014) and Zhang et al (2015b) (Xing and Liu 2016;Xu et al 2016). Therefore, seasonal isotope data on various sewage sources could be used as better SIAR input data, and tighter ranges of NO 3 − isotope data may contribute to more precise results from SIAR.…”