No Longer a Paradox: The Interaction Between Physical Transport and Biological Processes Explains th

The majority of lakes worldwide are oversaturated with methane (CH4) relative to the atmosphere, meaning that inland waters are a constant source of CH4, a potent greenhouse gas. In November 2017, the final manuscript for this oversaturation project was published in Ecosystems. We have found that the ubiquitous CH4 oversaturation seen in lakes globally should not be considered a paradox any longer! We developed a model that describes the physical transport of CH4 via horizontal dispersion and gas exchange from the littoral zone towards the center of lakes. Using data from a diverse set of Quebec lakes, as well as Lakes Ontario and Champlain, we found that physics alone can explain the majority of the spatial trend observed in surface water CH4, but the models tend to under predict the true concentrations towards the center of lakes, particularly large ones. Coupling the stable carbon isotopic (δ13C) changes of surface CH4 with concentration trends allowed us to determine the net impact of the biological processes modulating surface CH4. Ultimately, both CH4 oxidation and CH4 production in oxic waters contributes to surface CH4 trends and we found that 70% of our lakes exhibited a net productive signal. Thus, CH4 production in oxic surface waters appears to be a prevalent process in lakes of North America. This project has been conducted in collaboration with Yves Prairie and Paul del Giorgio at the University of Quebec at Montreal. You can find the paper here.