{"title":"水生系统中溶解态氮同位素的高精度分析技术：生物地球化学应用和溶解度平衡同位素效应的测定","authors":"Katelyn McPaul, Scott D. Wankel, Alan M. Seltzer","doi":"10.1002/rcm.10094","DOIUrl":null,"url":null,"abstract":"<div>\n \n \n <section>\n \n <h3> Rationale</h3>\n \n <p>The isotopic composition of dissolved dinitrogen gas (δ<sup>15</sup>N-N<sub>2</sub>) in water can offer a powerful constraint on the sources and pathways of nitrogen cycling in aquatic systems. However, because of the large presence of atmosphere-derived dissolved N<sub>2</sub> in these systems, high-precision (on the order of 0.001‰) measurements of N<sub>2</sub> isotopes paired with inert gas measurements are required to disentangle atmospheric and biogeochemical signals. Additionally, the solubility equilibrium isotope fractionation of N<sub>2</sub> and its temperature and salinity dependence are underconstrained at this level of precision.</p>\n </section>\n \n <section>\n \n <h3> Methods</h3>\n \n <p>We introduce a new technique for sample collection, processing, and dynamic dual-inlet mass spectrometry allowing for high-precision measurement of δ<sup>15</sup>N-N<sub>2</sub> and δ(N<sub>2</sub>/Ar) with simultaneous measurement of δ(<sup>40</sup>Ar/<sup>36</sup>Ar) and δ(Kr/N<sub>2</sub>) in water. We evaluate the reproducibility of this technique and employ it to redetermine the solubility equilibrium isotope effects for dissolved N<sub>2</sub> across a range of temperatures and salinities.</p>\n </section>\n \n <section>\n \n <h3> Results</h3>\n \n <p>Our technique achieves measurement reproducibility (1σ) for δ<sup>15</sup>N-N<sub>2</sub> (0.006‰) and δ(N<sub>2</sub>/Ar) (0.41‰) suitable for tracing biogeochemical nitrogen cycling in aquatic environments. Through a series of air–water equilibration experiments, we find a N<sub>2</sub> solubility equilibrium isotope effect (ε = α/1000 − 1, where α = (<sup>29</sup>N<sub>2</sub>/<sup>28</sup>N<sub>2</sub>)<sub>dissolved</sub>/(<sup>29</sup>N<sub>2</sub>/<sup>28</sup>N<sub>2</sub>)<sub>gas</sub>) in water of ε(‰) = 0.753 − 0.004•<i>T</i> where <i>T</i> is the temperature (°C), with uncertainties on the order of 0.001‰ over the temperature range of ~2°C–23°C and salinity range of ~0–30 psu. We find no apparent dependence of ε on salinity.</p>\n </section>\n \n <section>\n \n <h3> Conclusions</h3>\n \n <p>Our new method allows for high-precision measurements of the isotopic composition of dissolved N<sub>2</sub> and Ar, and dissolved N<sub>2</sub>/Ar and Kr/N<sub>2</sub> ratios, within the same sample. Pairing measurements of N<sub>2</sub> with inert gases facilitates the quantification of excess N<sub>2</sub> from biogeochemical sources and its isotopic composition. This method allows for a wide range of applications in marine, coastal, and freshwater environments to characterize and quantitatively constrain potential nitrogen-cycling sources and pathways and to differentiate between physical and biological isotope signals in these systems.</p>\n </section>\n </div>","PeriodicalId":225,"journal":{"name":"Rapid Communications in Mass Spectrometry","volume":"39 19","pages":""},"PeriodicalIF":1.7000,"publicationDate":"2025-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/rcm.10094","citationCount":"0","resultStr":"{\"title\":\"A High-Precision Analytical Technique for Dissolved N2 Isotopes in Aquatic Systems: Biogeochemical Applications and Determination of Solubility Equilibrium Isotope Effects\",\"authors\":\"Katelyn McPaul, Scott D. Wankel, Alan M. Seltzer\",\"doi\":\"10.1002/rcm.10094\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div>\\n \\n \\n <section>\\n \\n <h3> Rationale</h3>\\n \\n <p>The isotopic composition of dissolved dinitrogen gas (δ<sup>15</sup>N-N<sub>2</sub>) in water can offer a powerful constraint on the sources and pathways of nitrogen cycling in aquatic systems. However, because of the large presence of atmosphere-derived dissolved N<sub>2</sub> in these systems, high-precision (on the order of 0.001‰) measurements of N<sub>2</sub> isotopes paired with inert gas measurements are required to disentangle atmospheric and biogeochemical signals. Additionally, the solubility equilibrium isotope fractionation of N<sub>2</sub> and its temperature and salinity dependence are underconstrained at this level of precision.</p>\\n </section>\\n \\n <section>\\n \\n <h3> Methods</h3>\\n \\n <p>We introduce a new technique for sample collection, processing, and dynamic dual-inlet mass spectrometry allowing for high-precision measurement of δ<sup>15</sup>N-N<sub>2</sub> and δ(N<sub>2</sub>/Ar) with simultaneous measurement of δ(<sup>40</sup>Ar/<sup>36</sup>Ar) and δ(Kr/N<sub>2</sub>) in water. We evaluate the reproducibility of this technique and employ it to redetermine the solubility equilibrium isotope effects for dissolved N<sub>2</sub> across a range of temperatures and salinities.</p>\\n </section>\\n \\n <section>\\n \\n <h3> Results</h3>\\n \\n <p>Our technique achieves measurement reproducibility (1σ) for δ<sup>15</sup>N-N<sub>2</sub> (0.006‰) and δ(N<sub>2</sub>/Ar) (0.41‰) suitable for tracing biogeochemical nitrogen cycling in aquatic environments. Through a series of air–water equilibration experiments, we find a N<sub>2</sub> solubility equilibrium isotope effect (ε = α/1000 − 1, where α = (<sup>29</sup>N<sub>2</sub>/<sup>28</sup>N<sub>2</sub>)<sub>dissolved</sub>/(<sup>29</sup>N<sub>2</sub>/<sup>28</sup>N<sub>2</sub>)<sub>gas</sub>) in water of ε(‰) = 0.753 − 0.004•<i>T</i> where <i>T</i> is the temperature (°C), with uncertainties on the order of 0.001‰ over the temperature range of ~2°C–23°C and salinity range of ~0–30 psu. We find no apparent dependence of ε on salinity.</p>\\n </section>\\n \\n <section>\\n \\n <h3> Conclusions</h3>\\n \\n <p>Our new method allows for high-precision measurements of the isotopic composition of dissolved N<sub>2</sub> and Ar, and dissolved N<sub>2</sub>/Ar and Kr/N<sub>2</sub> ratios, within the same sample. Pairing measurements of N<sub>2</sub> with inert gases facilitates the quantification of excess N<sub>2</sub> from biogeochemical sources and its isotopic composition. This method allows for a wide range of applications in marine, coastal, and freshwater environments to characterize and quantitatively constrain potential nitrogen-cycling sources and pathways and to differentiate between physical and biological isotope signals in these systems.</p>\\n </section>\\n </div>\",\"PeriodicalId\":225,\"journal\":{\"name\":\"Rapid Communications in Mass Spectrometry\",\"volume\":\"39 19\",\"pages\":\"\"},\"PeriodicalIF\":1.7000,\"publicationDate\":\"2025-06-17\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"https://onlinelibrary.wiley.com/doi/epdf/10.1002/rcm.10094\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Rapid Communications in Mass Spectrometry\",\"FirstCategoryId\":\"92\",\"ListUrlMain\":\"https://onlinelibrary.wiley.com/doi/10.1002/rcm.10094\",\"RegionNum\":3,\"RegionCategory\":\"化学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q4\",\"JCRName\":\"BIOCHEMICAL RESEARCH METHODS\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Rapid Communications in Mass Spectrometry","FirstCategoryId":"92","ListUrlMain":"https://onlinelibrary.wiley.com/doi/10.1002/rcm.10094","RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q4","JCRName":"BIOCHEMICAL RESEARCH METHODS","Score":null,"Total":0}
A High-Precision Analytical Technique for Dissolved N2 Isotopes in Aquatic Systems: Biogeochemical Applications and Determination of Solubility Equilibrium Isotope Effects
Rationale
The isotopic composition of dissolved dinitrogen gas (δ15N-N2) in water can offer a powerful constraint on the sources and pathways of nitrogen cycling in aquatic systems. However, because of the large presence of atmosphere-derived dissolved N2 in these systems, high-precision (on the order of 0.001‰) measurements of N2 isotopes paired with inert gas measurements are required to disentangle atmospheric and biogeochemical signals. Additionally, the solubility equilibrium isotope fractionation of N2 and its temperature and salinity dependence are underconstrained at this level of precision.
Methods
We introduce a new technique for sample collection, processing, and dynamic dual-inlet mass spectrometry allowing for high-precision measurement of δ15N-N2 and δ(N2/Ar) with simultaneous measurement of δ(40Ar/36Ar) and δ(Kr/N2) in water. We evaluate the reproducibility of this technique and employ it to redetermine the solubility equilibrium isotope effects for dissolved N2 across a range of temperatures and salinities.
Results
Our technique achieves measurement reproducibility (1σ) for δ15N-N2 (0.006‰) and δ(N2/Ar) (0.41‰) suitable for tracing biogeochemical nitrogen cycling in aquatic environments. Through a series of air–water equilibration experiments, we find a N2 solubility equilibrium isotope effect (ε = α/1000 − 1, where α = (29N2/28N2)dissolved/(29N2/28N2)gas) in water of ε(‰) = 0.753 − 0.004•T where T is the temperature (°C), with uncertainties on the order of 0.001‰ over the temperature range of ~2°C–23°C and salinity range of ~0–30 psu. We find no apparent dependence of ε on salinity.
Conclusions
Our new method allows for high-precision measurements of the isotopic composition of dissolved N2 and Ar, and dissolved N2/Ar and Kr/N2 ratios, within the same sample. Pairing measurements of N2 with inert gases facilitates the quantification of excess N2 from biogeochemical sources and its isotopic composition. This method allows for a wide range of applications in marine, coastal, and freshwater environments to characterize and quantitatively constrain potential nitrogen-cycling sources and pathways and to differentiate between physical and biological isotope signals in these systems.
期刊介绍：
Rapid Communications in Mass Spectrometry is a journal whose aim is the rapid publication of original research results and ideas on all aspects of the science of gas-phase ions; it covers all the associated scientific disciplines. There is no formal limit on paper length ("rapid" is not synonymous with "brief"), but papers should be of a length that is commensurate with the importance and complexity of the results being reported. Contributions may be theoretical or practical in nature; they may deal with methods, techniques and applications, or with the interpretation of results; they may cover any area in science that depends directly on measurements made upon gaseous ions or that is associated with such measurements.
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