Methanotrophy in a boreal lake throughout winter and shoulder seasons

Climate change is shortening the duration and extent of ice cover on lakes, especially in boreal regions, and there is growing awareness about the impact of winters on the ecosystems. Methanotrophs are thought to play a crucial role in limiting CH4 emissions from the anoxic sediments into the atmosphere, in which its accumulation contributes to climate change, yet little is known on their seasonal dynamics or how they will respond to changing durations of ice cover and winter oxygen regimes due to warming. While hypoxic conditions under ice may slow microbial metabolism, the trapping of CH4 under ice preventing its diffusion into the atmosphere may allow for longer periods of time for methanotrophs to metabolize it - duration of ice may therefore promote CH4 oxidation. We present a 9-month temporal study of methanotrophs and dissolved GHG in a boreal lake, where we explored the impact of winter on CH4 accumulation and emission. Here, we present seasonal variations of microbial organisms, including methanotrophs and the gene encoding their methane-oxidization capability (pmoA) in Lake Simoncouche before, during and after the ice-cover period. We found that the ice cover impacted microbial communities and GHG concentrations. It was determined that CH4 and TN were drivers of methanotrophic activity in our study which happened mostly in oxygen depleted conditions with a peak in spring. Seasonal variations among methanotrophs genera were also present, notably for Methylobacter and Candidatus Methylacidiphilum. Signs of methanotrophy were also found in the lake ice.