{"title":"Methane Clumped Isotopologue Variability from Ebullition in a Mid-latitude Lake","authors":"Ellen Lalk*, Amber Velez and Shuhei Ono, ","doi":"10.1021/acsearthspacechem.3c00282","DOIUrl":null,"url":null,"abstract":"<p >Methane is a greenhouse gas and is an important component of carbon cycling in freshwater environments. Isotope ratios of methane (<sup>13</sup>C/<sup>12</sup>C and D/H) are used extensively as tracers to identify methane sources. Recent advances in the measurement of clumped methane isotopologues (<sup>13</sup>CH<sub>3</sub>D, <sup>12</sup>CH<sub>2</sub>D<sub>2</sub>) offer new opportunities to constrain sources and sinks of atmospheric methane. Previous measurements of clumped methane isotopologues from freshwater environments have been spatially and temporally limited. The abundance of <sup>13</sup>CH<sub>3</sub>D and methane flux from ebullition in the deep basin of Upper Mystic Lake were measured from May to November 2021 to characterize the source isotopologue signatures and methane fluxes for mid-latitude lakes. The trends in δ<sup>13</sup>C and δD values support decreased methane oxidation in the early summer compared to fall. The Δ<sup>13</sup>CH<sub>3</sub>D values from this study range from 2.0 to 4.2‰, reflecting methane oxidation occurring anaerobically in lake sediments and euxinic bottom waters at sample sites. The relatively large variation in the Δ<sup>13</sup>CH<sub>3</sub>D values observed within this lake basin aligns with previous observations of bubbles from arctic lakes. The values of Δ<sup>13</sup>CH<sub>3</sub>D do not correlate with methane flux, suggesting that Δ<sup>13</sup>CH<sub>3</sub>D measurements from background ebullition are not sensitive as a proxy for ebullition rates. This study presents a uniquely large (<i>n</i> = 40) set of freshwater Δ<sup>13</sup>CH<sub>3</sub>D values from a single lake basin, which we use to recommend a sampling strategy of ≥9 samples to constrain the Δ<sup>13</sup>CH<sub>3</sub>D source signal within ∼0.5‰ from similar environments. This data demonstrates the utility of clumped methane isotopologues to gain insights into local biogeochemical processes from field studies and points to the challenge of using clumped isotopologue measurements to constrain global freshwater–methane sources to the atmosphere.</p>","PeriodicalId":15,"journal":{"name":"ACS Earth and Space Chemistry","volume":null,"pages":null},"PeriodicalIF":2.9000,"publicationDate":"2024-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"ACS Earth and Space Chemistry","FirstCategoryId":"92","ListUrlMain":"https://pubs.acs.org/doi/10.1021/acsearthspacechem.3c00282","RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"CHEMISTRY, MULTIDISCIPLINARY","Score":null,"Total":0}
引用次数: 0
Abstract
Methane is a greenhouse gas and is an important component of carbon cycling in freshwater environments. Isotope ratios of methane (13C/12C and D/H) are used extensively as tracers to identify methane sources. Recent advances in the measurement of clumped methane isotopologues (13CH3D, 12CH2D2) offer new opportunities to constrain sources and sinks of atmospheric methane. Previous measurements of clumped methane isotopologues from freshwater environments have been spatially and temporally limited. The abundance of 13CH3D and methane flux from ebullition in the deep basin of Upper Mystic Lake were measured from May to November 2021 to characterize the source isotopologue signatures and methane fluxes for mid-latitude lakes. The trends in δ13C and δD values support decreased methane oxidation in the early summer compared to fall. The Δ13CH3D values from this study range from 2.0 to 4.2‰, reflecting methane oxidation occurring anaerobically in lake sediments and euxinic bottom waters at sample sites. The relatively large variation in the Δ13CH3D values observed within this lake basin aligns with previous observations of bubbles from arctic lakes. The values of Δ13CH3D do not correlate with methane flux, suggesting that Δ13CH3D measurements from background ebullition are not sensitive as a proxy for ebullition rates. This study presents a uniquely large (n = 40) set of freshwater Δ13CH3D values from a single lake basin, which we use to recommend a sampling strategy of ≥9 samples to constrain the Δ13CH3D source signal within ∼0.5‰ from similar environments. This data demonstrates the utility of clumped methane isotopologues to gain insights into local biogeochemical processes from field studies and points to the challenge of using clumped isotopologue measurements to constrain global freshwater–methane sources to the atmosphere.
期刊介绍:
The scope of ACS Earth and Space Chemistry includes the application of analytical, experimental and theoretical chemistry to investigate research questions relevant to the Earth and Space. The journal encompasses the highly interdisciplinary nature of research in this area, while emphasizing chemistry and chemical research tools as the unifying theme. The journal publishes broadly in the domains of high- and low-temperature geochemistry, atmospheric chemistry, marine chemistry, planetary chemistry, astrochemistry, and analytical geochemistry. ACS Earth and Space Chemistry publishes Articles, Letters, Reviews, and Features to provide flexible formats to readily communicate all aspects of research in these fields.