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Paradox reconsidered: Methane oversaturation in well‐oxygenated lake waters
Author(s) -
Tang Kam W.,
McGinnis Daniel F.,
Frindte Katharina,
Brüchert Volker,
Grossart Hans-Peter
Publication year - 2014
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.2014.59.1.0275
Subject(s) - methane , anoxic waters , anaerobic oxidation of methane , methanogenesis , water column , environmental chemistry , thermocline , oxygen , chemistry , bottom water , environmental science , geology , oceanography , organic chemistry
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.