Opposing Effects of Climate and Permafrost Thaw on CH₄ and CO₂ Emissions From Northern Lakes

Abstract

Abstract Small, organic‐rich lakes are important sources of methane (CH 4 ) and carbon dioxide (CO 2 ) to the atmosphere, yet the sensitivity of emissions to climate warming is poorly constrained and potentially influenced by permafrost thaw. Here, we monitored emissions from 20 peatland lakes across a 1,600 km permafrost transect in boreal western Canada. Contrary to expectations, we observed a shift from source to sink of CO 2 for lakes warmer regions, driven by greater primary productivity associated with greater hydrological connectivity to lakes and nutrient availability in the absence of permafrost. Conversely, an 8‐fold increase in CH 4 emissions in warmer regions was associated with water temperature and shifts in microbial communities and dominant anaerobic processes. Our results suggest that the net radiative forcing from altered greenhouse gas emissions of northern peatland lakes this century will be dominated by increasing CH 4 emissions and only partially offset by reduced CO 2 emissions.