Claudia Frey, Weiyi Tang, Bess B. Ward, Moritz F. Lehmann
{"title":"Sample preservation methods for nitrous oxide concentration and isotope ratio measurements in aquatic environments","authors":"Claudia Frey, Weiyi Tang, Bess B. Ward, Moritz F. Lehmann","doi":"10.1002/lom3.10638","DOIUrl":null,"url":null,"abstract":"<p>The nitrogen (N) and oxygen (O) stable isotope analysis of dissolved nitrous oxide (N<sub>2</sub>O) can provide important constraints on the sources and cycling of N<sub>2</sub>O in aquatic environments. The isotopic composition of aqueous N<sub>2</sub>O, both in field (natural abundance) or experimental (<sup>15</sup>N-labeling) samples, however, may be altered by abiotic reactions involving nitrite (<span></span><math>\n <mrow>\n <msubsup>\n <mi>NO</mi>\n <mn>2</mn>\n <mo>−</mo>\n </msubsup>\n </mrow></math>) or hydroxylamine (NH<sub>2</sub>OH) and microbial activity during sample storage, if samples are not adequately preserved. Here we tested five different preservatives, mercuric chloride (HgCl<sub>2</sub>), copper sulfate (CuSO<sub>4</sub>), zinc chloride (ZnCl<sub>2</sub>), hydrochloric acid (HCl) mixed with sulfamic acid (SFA), and sodium hydroxide (NaOH), for fixing natural water samples from an estuary and a lake with different <span></span><math>\n <mrow>\n <msubsup>\n <mi>NO</mi>\n <mn>2</mn>\n <mo>−</mo>\n </msubsup>\n </mrow></math> concentrations over a range of different storage times for N<sub>2</sub>O analyses. ZnCl<sub>2</sub> and CuSO<sub>4</sub> decreased the pH, and led to abiotic N<sub>2</sub>O production from <span></span><math>\n <mrow>\n <msup>\n <mrow>\n <mo> </mo>\n </mrow>\n <mn>15</mn>\n </msup>\n <mi>N</mi>\n <msubsup>\n <mi>O</mi>\n <mn>2</mn>\n <mo>−</mo>\n </msubsup>\n </mrow></math>, shifting the N<sub>2</sub>O isotopic composition significantly. Removal of <span></span><math>\n <mrow>\n <msubsup>\n <mi>NO</mi>\n <mn>2</mn>\n <mo>−</mo>\n </msubsup>\n </mrow></math> with a mixture of SFA and HCl did not always prevent the alteration of the original N and O isotope composition of N<sub>2</sub>O, confirming the requirement for complete <span></span><math>\n <mrow>\n <msubsup>\n <mi>NO</mi>\n <mn>2</mn>\n <mo>−</mo>\n </msubsup>\n </mrow></math> removal, and underscoring the biasing effects of <span></span><math>\n <mrow>\n <msubsup>\n <mi>NO</mi>\n <mn>2</mn>\n <mo>−</mo>\n </msubsup>\n </mrow></math> at very low pH, even at trace levels. At low <span></span><math>\n <mrow>\n <msubsup>\n <mi>NO</mi>\n <mn>2</mn>\n <mo>−</mo>\n </msubsup>\n </mrow></math> background, HgCl<sub>2</sub> preservation led to robust and accurate results. However, in light of its toxicity and bioaccumulation potential in food webs, this fixative should be avoided. The addition of NaOH reduced abiotic side reactions involving <span></span><math>\n <mrow>\n <msubsup>\n <mi>NO</mi>\n <mn>2</mn>\n <mo>−</mo>\n </msubsup>\n </mrow></math>, and yielded the most reliable and reproducible results for N<sub>2</sub>O concentration and isotope ratio measurements across tested settings and storage times.</p>","PeriodicalId":18145,"journal":{"name":"Limnology and Oceanography: Methods","volume":null,"pages":null},"PeriodicalIF":2.1000,"publicationDate":"2024-07-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/lom3.10638","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Limnology and Oceanography: Methods","FirstCategoryId":"89","ListUrlMain":"https://onlinelibrary.wiley.com/doi/10.1002/lom3.10638","RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"LIMNOLOGY","Score":null,"Total":0}
引用次数: 0
Abstract
The nitrogen (N) and oxygen (O) stable isotope analysis of dissolved nitrous oxide (N2O) can provide important constraints on the sources and cycling of N2O in aquatic environments. The isotopic composition of aqueous N2O, both in field (natural abundance) or experimental (15N-labeling) samples, however, may be altered by abiotic reactions involving nitrite () or hydroxylamine (NH2OH) and microbial activity during sample storage, if samples are not adequately preserved. Here we tested five different preservatives, mercuric chloride (HgCl2), copper sulfate (CuSO4), zinc chloride (ZnCl2), hydrochloric acid (HCl) mixed with sulfamic acid (SFA), and sodium hydroxide (NaOH), for fixing natural water samples from an estuary and a lake with different concentrations over a range of different storage times for N2O analyses. ZnCl2 and CuSO4 decreased the pH, and led to abiotic N2O production from , shifting the N2O isotopic composition significantly. Removal of with a mixture of SFA and HCl did not always prevent the alteration of the original N and O isotope composition of N2O, confirming the requirement for complete removal, and underscoring the biasing effects of at very low pH, even at trace levels. At low background, HgCl2 preservation led to robust and accurate results. However, in light of its toxicity and bioaccumulation potential in food webs, this fixative should be avoided. The addition of NaOH reduced abiotic side reactions involving , and yielded the most reliable and reproducible results for N2O concentration and isotope ratio measurements across tested settings and storage times.
期刊介绍:
Limnology and Oceanography: Methods (ISSN 1541-5856) is a companion to ASLO''s top-rated journal Limnology and Oceanography, and articles are held to the same high standards. In order to provide the most rapid publication consistent with high standards, Limnology and Oceanography: Methods appears in electronic format only, and the entire submission and review system is online. Articles are posted as soon as they are accepted and formatted for publication.
Limnology and Oceanography: Methods will consider manuscripts whose primary focus is methodological, and that deal with problems in the aquatic sciences. Manuscripts may present new measurement equipment, techniques for analyzing observations or samples, methods for understanding and interpreting information, analyses of metadata to examine the effectiveness of approaches, invited and contributed reviews and syntheses, and techniques for communicating and teaching in the aquatic sciences.