Factors controlling methane oxidation in shield lakes: The role of nitrogen fixation and oxygen concentration1

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Abstract
During summer stratification methane‐oxidizing bacteria in Lake 227 are confined to a narrow zone within the thermocline because of their sensitivity to high epilimnetic oxygen concentrations. This oxygen sensitivity is based on the dependence of the oxidizers on an oxygen‐sensitive nitrogen fixation process. Thus epilimnetic methane oxidation is absent during periods of nitrogen limitation, since high epilimnetic oxygen concentrations prevent nitrogen fixation. During periods of overturn and throughout the winter, the methane oxidizers become oxygen insensitive and oxidation occurs rapidly throughout the water column. This oxygen insensitivity likely occurs as a result of high in situ concentrations of dissolved inorganic nitrogen, which replaces nitrogen fixation as a source for fixed nitrogen. Under ice‐cover, rapid methane oxidation throughout the water column can be a major cause of total anoxia.

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