Climate-driven shifts in sediment chemistry enhance methane production in northern lakes

Freshwater ecosystems are a major source of methane (CH4), contributing 0.65 Pg (in CO2 equivalents) yr-1 towards global carbon (C) emissions and thereby offsetting [~]25% of the terrestrial carbon sink. Most CH4 emissions come from littoral sediments, where large quantities of plant material are decomposed. As climate change is predicted to shift plant community composition, and thus change the quality of inputs into detrital food webs, this can affect CH4 production and have far-reaching consequences for global C emissions. Here we find that variation in polyphenol availability from decomposing organic matter underlies large differences in CH4 production in lake sediments. Production was at least 400-times higher from sediments composed of macrophyte litter compared to terrestrial sources (coniferous and deciduous), which we link to the inhibition of methanogenesis by polyphenol leachates. Applying our estimates to projected northward advances in the distribution of Typha latifolia, a widespread and dominant macrophyte, we find that CH4 production could increase by at least 73% in the lake-rich Boreal Shield ecozone solely due to increases in this one macrophyte species. Our results now suggest that earth system models and carbon budgets should consider the effects of plant communities on sediment chemistry and ultimately CH4 emissions at a global scale.\n\nOne-sentence summaryProduction of methane from lakes is at least 400-times lower when 24 sediments receive forest- as opposed to macrophyte-derived (Typha latifolia) litterfall.