Abstract
AbstractWinter methane (CH4) accumulation in seasonally ice‐covered lakes can contribute to large episodic emissions to the atmosphere during spring ice melt. Biological methane oxidation can significantly mitigate such CH4 emissions, but despite favorable CH4 and O2 concentrations, CH4 oxidation appears constrained in some lakes for unknown reasons. Here we experimentally test the hypothesis that phosphorus (P) availability is limiting CH4 oxidation, resulting in differences in ice‐out emissions among lakes. We observed a positive relationship between potential CH4 oxidation and P concentration across 12 studied lakes and found an increase in CH4 oxidation in response to P amendment, without any parallel change in the methanotrophic community composition. Hence, while an increase in sedimentary CH4 production and ebullitive emissions may happen with eutrophication, our study indicates that the increase in P associated with eutrophication may also enhance CH4 oxidation. The increase in CH4 oxidation may hence play an important role in nutrient‐rich ice‐covered lakes where bubbles trapped under the ice may to a greater extent be oxidized, reducing the ice‐out emissions of CH4. This may be an important factor regulating CH4 emissions from high latitude lakes.
Highlights
IntroductionEspecially in northern lakes, may increase CH4 emissions by up to 54% (Wik et al, 2016)
Lakes are important global sources of CH4 to the atmosphere
Based on the overall positive response of CH4 oxidation to phosphate addition observed in the experiment, we conclude that when CH4 and O2 are not limiting factors, CH4 oxidation in lakes could be constrained by P availability
Summary
Especially in northern lakes, may increase CH4 emissions by up to 54% (Wik et al, 2016). This increase may be exacerbated by eutrophication (Beaulieu et al, 2019; DelSontro et al, 2018). Half of the global lake surface area is located in temperate and boreal zones where lakes are ice-covered for some period in the winter (Downing et al, 2006; Matthews et al, 2020). The observations of CH4-rich bubbles under lake ice at the end of the winter and associated emissions upon ice-out are mysterious for several reasons. The observations of CH4-rich bubbles under lake ice at the end of the winter and associated emissions upon ice-out are mysterious for several reasons. (a) This CH4 is exposed to oxic water for extended periods, which should create favorable conditions for CH4 oxidation, known to have the capacity to deplete water column
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