Abstract
Lakes are a major component of boreal landscapes, and whereas lake CO 2 emissions are recognized as a major component of regional C budgets, there is still much uncertainty associated to lake CH 4 fluxes. Here, we present a large‐scale study of the magnitude and regulation of boreal lake summer diffusive CH 4 fluxes, and their contribution to total lake carbon (C) emissions, based on in situ measurements of concentration and fluxes of CH 4 and CO 2 in 224 lakes across a wide range of lake type and environmental gradients in Québec. The diffusive CH 4 flux was highly variable (mean 11.6 ± 26.4 SD mg m −2 d −1 ), and it was positively correlated with temperature and lake nutrient status, and negatively correlated with lake area and colored dissolved organic matter ( CDOM ). The relationship between CH 4 and CO 2 concentrations fluxes was weak, suggesting major differences in their respective sources and/or regulation. For example, increasing water temperature leads to higher CH 4 flux but does not significantly affect CO 2 flux, whereas increasing CDOM concentration leads to higher CO 2 flux but lower CH 4 flux. CH 4 contributed to 8 ± 23% to the total lake C emissions ( CH 4 + CO 2 ), but 18 ± 25% to the total flux in terms of atmospheric warming potential, expressed as CO 2 ‐equivalents. The incorporation of ebullition and plant‐mediated CH 4 fluxes would further increase the importance of lake CH 4 . The average Q 10 of CH 4 flux was 3.7, once other covarying factors were accounted for, but this apparent Q 10 varied with lake morphometry and was higher for shallow lakes. We conclude that global climate change and the resulting shifts in temperature will strongly influence lake CH 4 fluxes across the boreal biome, but these climate effects may be altered by regional patterns in lake morphometry, nutrient status, and browning.