Greenhouse gas emission from lakes and impoundments: upscaling in the face of global change

Now published in Limnology & Oceanography Letters (https://doi.org/10.1002/lol2.10073) is a manuscript I worked on with Jake Beaulieu of the EPA and John Downing, Director of Minnesota Sea Grant on upscaling CO2, CH4 and N2O emissions from lakes and impoundments globally. We collected gas flux, nutrient, chlorophyll, and lake size data from the literature to compile a database with >8000 measurements from hundreds to thousands of systems depending on the gas. Based on mounting evidence that trophic state, productivity and lake size play the most important roles in aquatic gas emissions, we derived empirical models for each gas using the collected data.

Next, we used 3 different lake size distributions (as an official consensus does not currently exist) and satellite data of chlorophyll (as a proxy for productivity) to upscale the emissions of all three greenhouse gases globally. Comparing our values to previous estimates, we found that CO2 emissions may have been overestimated previously, while CH4 emissions were underestimated. N2O emissions were minor compared to the other gases. We also found that CH4 had the highest atmospheric impact of the three gases, despite CO2 emissions being higher in absolute terms. As the radiative forcing of CH4 is ~34x that of CO2, we find that the 75% of the climatic impact of aquatic greenhouse gas emissions is due to CH4 alone. Ultimately, in terms of climatic impact, total global aquatic greenhouse gas emission is equivalent to nearly 20% of global CO2 fossil fuel emission. Considering that productivity played a large role in the emissions of all three gases, but especially CH4, we should consider the health of our inland waters as we mitigate against global climate change.