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Paradox reconsidered: Methane oversaturation in well-oxygenated lake waters
Tang, KW McGinnis, DF Frindte, K Bruchert, V Grossart, HP
Tang, KW
McGinnis, DF
Frindte, K
Bruchert, V
Grossart, HP
Abstract
The widely reported paradox of methane oversaturation in oxygenated water challenges the prevailing paradigm that microbial methanogenesis only occurs under anoxic conditions. Using a combination of field sampling, incubation experiments, and modeling, we show that the recurring mid-water methane peak in Lake Stechlin, northeast Germany, was not dependent on methane input from the littoral zone or bottom sediment or on the presence of known micro-anoxic zones. The methane peak repeatedly overlapped with oxygen oversaturation in the seasonal thermocline. Incubation experiments and isotope analysis indicated active methane production, which was likely linked to photosynthesis and/or nitrogen fixation within the oxygenated water, whereas lessening of methane oxidation by light allowed accumulation of methane in the oxygen-rich upper layer. Estimated methane efflux from the surface water was up to 5 mmol m(-2) d(-1). Mid-water methane oversaturation was also observed in nine other lakes that collectively showed a strongly negative gradient of methane concentration within 0-20% dissolved oxygen (DO) in the bottom water, and a positive gradient within >= 20% DO in the upper water column. Further investigation into the responsible organisms and biochemical pathways will help improve our understanding of the global methane cycle.
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2014-01-01
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lo.2014.59.1.0275.pdf
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Biological Sciences Peer-Reviewed Articles, Carbon-Isotope Fractionation; Methanosarcina-Barkeri; Fresh-Water; Methanogenesis; Emissions; Hydrogen; Oxidation; Acetate; Column; Budget
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Virginia Institute of Marine Science
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https://doi.org/10.4319/lo.2014.59.1.0275