Variability and controls of stable carbon isotopic fractionation during aerobic methane oxidation in temperate lakes

The aerobic oxidation of methane (CH 4 ) by methanotrophic bacteria (MOB) is the major sink of this highly potent greenhouse gas in freshwater environments. Yet, CH 4 oxidation is one of the largest uncertain components in predicting the current and future CH 4 emissions from these systems. While st...

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Veröffentlicht in:Frontiers in environmental science 2022-09, Vol.10
Hauptverfasser: Thottathil, Shoji D., Reis, Paula C. J., Prairie, Yves T.
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Sprache:eng
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Zusammenfassung:The aerobic oxidation of methane (CH 4 ) by methanotrophic bacteria (MOB) is the major sink of this highly potent greenhouse gas in freshwater environments. Yet, CH 4 oxidation is one of the largest uncertain components in predicting the current and future CH 4 emissions from these systems. While stable carbon isotopic mass balance is a powerful approach to estimate the extent of CH 4 oxidation in situ , its applicability is constrained by the need of a reliable isotopic fractionation factor (α ox ), which depicts the slower reaction of the heavier stable isotope ( 13 C) during CH 4 oxidation. Here we explored the natural variability and the controls of α ox across the water column of six temperate lakes using experimental incubation of unamended water samples at different temperatures. We found a large variability of α ox (1.004–1.038) with a systematic increase from the surface to the deep layers of lake water columns. Moreover, α ox was strongly positively coupled to the abundance of MOB in the γ-proteobacteria class (γ-MOB), which in turn correlated to the concentrations of oxygen and CH 4 , and to the rates of CH 4 oxidation. To enable the applicability in future isotopic mass balance studies, we further developed a general model to predict α ox using routinely measured limnological variables. By applying this model to δ 13 C-CH 4 profiles obtained from the study lakes, we show that using a constant α ox value in isotopic mass balances can largely misrepresent and undermine patterns of the extent of CH 4 oxidation in lakes. Our α ox model thus contributes towards more reliable estimations of stable carbon isotope-based quantification of CH 4 oxidation and may help to elucidate large scale patterns and drivers of the oxidation-driven mitigation of CH 4 emission from lakes.
ISSN:2296-665X
2296-665X
DOI:10.3389/fenvs.2022.833688