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 |
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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. |
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ISSN: | 2296-665X 2296-665X |
DOI: | 10.3389/fenvs.2022.833688 |