Methane and nitrous oxide measured throughout Lake Erie over all seasons indicate highest emissions from the eutrophic Western Basin

Eutrophication has been linked to increased greenhouse gas emissions from inland waters. Phytoplankton blooms in Lake Erie have increased since the 1990s, although its greenhouse gas emissions are not well characterized. We measured CH4 and N2O concentrations and diffusive fluxes in four seasons around the entire lake, and CO2 fluxes in one summer season. Lake Erie is a source of CH4 all year across the lake, concentrated in spring and summer in the Western Basin. Methane emissions ranged from 0.03 to 14.87 mg C m(-2) d(-1). Methane is predominantly biogenic, and natural gas leaks are an insignificant source. While Lake Erie is an overall N2O source, it is an N2O sink in winter and occasionally during summer. Emissions of N2O ranged from -0.08 to 1.22 mg N m(-2) d(-1). We also measured CO2 fluxes in summer only, when Lake Erie is a small atmospheric CO2 sink. While areal fluxes of CH4 and N2O are similar to those observed elsewhere, total fluxes from Lake Erie are higher due to its surface area. Lake Erie emits similar to 6300 (+/- 19%) metric tons of CH4-C yr(-1) and similar to 600 (+/- 37%) metric tons N2O-N yr(-1): almost 500,000 metric tons CO2-eq yr(-1) total. This is the first comprehensive dataset of CH4 and N2O concentrations and diffusive emissions in a very large lake. More measurements and monitoring are needed to determine whether increased eutrophication in the Great Lakes is tied to increased emissions of these powerful climate forcers in a possible positive feedback to climate warming. (C) 2020 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved.