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The Extent and Regulation of Summer Methane Oxidation in Northern Lakes
Author(s) -
Thottathil Shoji D.,
Reis Paula C. J.,
Giorgio Paul A.,
Prairie Yves T.
Publication year - 2018
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1029/2018jg004464
Subject(s) - epilimnion , sink (geography) , dissolved organic carbon , water column , environmental chemistry , environmental science , anaerobic oxidation of methane , methane , aquatic ecosystem , chemistry , ecology , nutrient , hypolimnion , eutrophication , biology , geography , cartography , organic chemistry
Inland waters have a significant influence on atmospheric methane (CH 4 ) levels. However, processes determining the strength of CH 4 emissions from these systems are not well defined. Aerobic oxidation is a major sink of CH 4 in freshwater environments and thus an important determinant of aquatic CH 4 emissions, yet strikingly little is known about its drivers. Here we assessed the extent of water column CH 4 oxidation at the whole ecosystem scale using stable carbon isotopic (δ 13 C) mass balance of CH 4 in 14 northern lakes spanning wide range of dissolved organic carbon (DOC) concentrations. We show that the extent of oxidation can vary from near zero to near complete, and for concentrations of 1.9–11 mg/L, DOC is a key modulator of CH 4 oxidation during the summer stratification period. Increasing DOC concentrations enhances oxidation in the upper layers by reducing light inhibition on methanotrophic activity, while reducing oxygen available for oxidation in the deeper layers. The effect of this light inhibition was also observable over the diurnal cycle. We developed simple predictive empirical models ( r 2 > 0.82) to estimate the extent of oxidation in the different layers of lakes for the summer period. Applying our surface layer model to a larger data set suggests that about 30% of CH 4 transported to or generated within the epilimnion of Québec lakes is oxidized during summer. Our results imply that DOC concentration, through its effect on the light regime of lakes, has the potential to affect strongly the magnitude and patterns of summer CH 4 emissions.