A simple headspace equilibration method for measuring dissolved methane

Magen, Cédric; Lapham, L.; Pohlman, John W.; Marshall, Kathleen; Bosman, Samantha; Casso, M.; Chanton, Jeffrey P.

doi:10.4319/lom.2014.12.637

Cited by 122 publications

(118 citation statements)

References 42 publications

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“…Vials were stored inverted until shorebased analysis via gas chromatography. A complete description of our analytical techniques can be found in Magen et al (2014).…”

Section: Methanementioning

confidence: 99%

Methane and microbial dynamics in the Gulf of Mexico water column

et al. 2015

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In contrast to other oligotrophic water bodies the Gulf of Mexico (GOM) hosts an abundance of hydrocarbon seeps, which likely influences the microbial assemblages it hosts particularly regarding the availability of labile carbon in the aphotic GOM. The aphotic zone receives direct injection of seep methane (CH 4 ), but CH 4 from an unknown source has been reported at supersaturated concentrations relative to the atmosphere in the GOM photic zone. Here we used iTag sequencing of 16S rRNA genes to characterize GOM microbial communities and to relate changes in microbial community structure to the properties inherent to their oceanic province-seafloor to the photic zone, seep and non-seep. Along this trajectory water column communities were distinct in the euphotic zone compared to the mesopelagic and deep-sea. In the euphotic zone the relative abundance of a cyanobacterial species (Prochlorococcus) was significantly correlated with both CH 4 and chlorophyll a concentrations and was abundant in some deep-chlorophyll maximum (DCM) samples. The relative abundance of microorganisms related to known hydrocarbon degraders were also significantly correlated with CH 4 in the euphotic zone, but no canonical methanotrophs were observed. In the mesopelagic to the seafloor canonical methanotrophs were identified, but only a Marine Group II Euryarchaeota was significantly correlated with CH 4 . Overall, depth and the associated environmental conditions were the primary drivers in structuring microbial communities over the GOM water column. Further, CH 4 concentrations and relative microbial abundances covaried significantly from the seafloor to the photic zone in the GOM. The lack of a significant relationship between canonical methanotrophs and CH 4 in the aphotic zone, even when sampling at seep sites, may suggest methane-oxidation by unknown microorganisms. Similarly their absence in the CH 4 maximum and DCM suggested that CH 4 is either oxidized by unrecognized methanotrophs or escapes the CH 4 biofilter and fluxes to the atmosphere.

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“…Vials were stored inverted until shorebased analysis via gas chromatography. A complete description of our analytical techniques can be found in Magen et al (2014).…”

Section: Methanementioning

confidence: 99%

Methane and microbial dynamics in the Gulf of Mexico water column

et al. 2015

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“…Samples were poisoned with 0.3 mL of 25 % H 2 SO 4 , stored upside down at temperatures < 15 • C, and analysed after 4 months. Glass bottles and butyl stoppers are relatively methane tight and acidification of water samples results in good long-term sample preservation (Magen et al, 2014;Taipale and Sonninen, 2009). However, we cannot exclude the possibility that some methane was lost from the samples.…”

Section: Water Sampling and Gas Analysismentioning

confidence: 99%

“…Gas standards (Air Liquide) with methane concentrations of 10 and 100 ppm were used for calibration. The calculation of the methane concentration was performed according to Magen et al (2014), taking into account the different methane solubilities at the wide range of salinities (1-33). The precision of the calibration line was r 2 = 0.99 and the reproducibility of the samples was 7 %.…”

Section: Water Sampling and Gas Analysismentioning

confidence: 99%

Methane distribution and oxidation around the Lena Delta in summer 2013

et al. 2017

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Abstract. The Lena River is one of the largest Russian rivers draining into the Laptev Sea. The predicted increases in global temperatures are expected to cause the permafrost areas surrounding the Lena Delta to melt at increasing rates. This melting will result in high amounts of methane reaching the waters of the Lena and the adjacent Laptev Sea. The only biological sink that can lower methane concentrations within this system is methane oxidation by methanotrophic bacteria. However, the polar estuary of the Lena River, due to its strong fluctuations in salinity and temperature, is a challenging environment for bacteria. We determined the activity and abundance of aerobic methanotrophic bacteria by a tracer method and by the quantitative polymerase chain reaction. We described the methanotrophic population with a molecular fingerprinting method (monooxygenase intergenic spacer analysis), as well as the methane distribution (via a headspace method) and other abiotic parameters, in the Lena Delta in September 2013.The median methane concentrations were 22 nmol L −1 for riverine water (salinity (S) < 5), 19 nmol L −1 for mixed water (5 < S < 20) and 28 nmol L −1 for polar water (S > 20). The Lena River was not the source of methane in surface water, and the methane concentrations of the bottom water were mainly influenced by the methane concentration in surface sediments. However, the bacterial populations of the riverine and polar waters showed similar methane oxidation rates (0.419 and 0.400 nmol L −1 d −1 ), despite a higher relative abundance of methanotrophs and a higher estimated diversity in the riverine water than in the polar water. The methane turnover times ranged from 167 days in mixed water and 91 days in riverine water to only 36 days in polar water. The environmental parameters influencing the methane oxidation rate and the methanotrophic population also differed between the water masses. We postulate the presence of a riverine methanotrophic population that is limited by sub-optimal temperatures and substrate concentrations and a polar methanotrophic population that is well adapted to the cold and methane-poor polar environment but limited by a lack of nitrogen. The diffusive methane flux into the atmosphere ranged from 4 to 163 µmol m 2 d −1 (median 24). The diffusive methane flux accounted for a loss of 8 % of the total methane inventory of the investigated area, whereas the methanotrophic bacteria consumed only 1 % of this methane inventory. Our results underscore the importance of measuring the methane oxidation activities in polar estuaries, and they indicate a population-level differentiation between riverine and polar water methanotrophs.

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“…Dissolved gas analysis involves headspace, purge and tramp, microextraction, and stripping techniques which separate dissolved gases from a liquid matrix and use specialized instruments to measure their concentrations (Jones and Schuberth, 1989;Snow and Slack, 2002;Stashenko and Martínez, 2010;Magen et al, 2014). Gas chromatography (GC) is the most frequently used technique, due to its accuracy of gas measurements such as methane (CH 4 ) and nitrous oxide (N 2 O).…”

Section: Introductionmentioning

confidence: 99%

Toward High-Resolution Vertical Measurements of Dissolved Greenhouse Gases (Nitrous Oxide and Methane) and Nutrients in the Eastern South Pacific

2018

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In this study, in situ, real-time and high-resolution vertical measurements of dissolved greenhouse gases (GHGs) such as nitrous oxide (N 2 O) and methane (CH 4 ) and nutrients are reported for the eastern South Pacific (ESP); a region with marked zonal gradients, ranging from highly productive and suboxic conditions in coastal upwelling systems to oligotrophic and oxygenated conditions in the subtropical gyre. Four high-resolution vertical profiles for gases (N 2 O and CH 4 ) and nutrients (NO − 3 and PO 3− 4 ) were measured using a Pumped Profiling System (PPS), connected with a liquid degassing membrane coupled with Cavity Ring-Down Spectroscopy (CRDS) and a nutrient auto-analyzer, respectively. The membrane-CRDS system maintains a linear response over a wide range of gas concentrations, detecting N 2 O and CH 4 levels as low as 0.0774 ± 0.0004 and 0.1011 ± 0.001 ppm, respectively. Continuous profiles for gases and nutrients were similar to those reported throughout the ESP, with pronounced N 2 O and CH 4 peaks at the upper oxycline and at the base of the euphotic zone and pycnocline, respectively, in the coastal zone; but almost constant depth profiles in the subtropical gyre. Additionally, other vertical gas and nutrient structures were observed using continuous sampling, which would not have been detected by discrete sampling. Our results demonstrate that continuous measurements can be a potentially useful methodology for future GHGs cycle studies.

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A simple headspace equilibration method for measuring dissolved methane

Cited by 122 publications

References 42 publications

Methane and microbial dynamics in the Gulf of Mexico water column

Methane and microbial dynamics in the Gulf of Mexico water column

Methane distribution and oxidation around the Lena Delta in summer 2013

Toward High-Resolution Vertical Measurements of Dissolved Greenhouse Gases (Nitrous Oxide and Methane) and Nutrients in the Eastern South Pacific

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