Methane oxidation in African lakes increases with phytoplankton and outweighs photosynthesis-driven oxic methane production

Lakes are large natural sources of methane (CH4), a potent greenhouse gas, resulting from the net balance of inputs from anaerobic and oxic methane production (OMP) and removal by methane oxidation (MOX). Here we investigate spatial patterns and causes of MOX variability in 79 African lakes. MOX is highest in the most productive lakes presumably due to methanotrophs attached to phytoplankton, as well as in lakes draining the wetlands of the Congo basin presumably due to inputs of methanotrophs from flooded forest soils. MOX represents the largest sink of dissolved CH4 in the mixed layer (>70%) compared to the diffusive emission to the atmosphere (FCH4). Photosynthesis-driven OMP estimated from literature data represents a small fraction of both MOX and FCH4, and this fraction decreases with lake productivity and FCH4 intensity. Available evidence suggests that photosynthesis-driven OMP increase supported by eutrophication can be compensated by a stronger increase in MOX.