Constraining methane emissions and sources in the North American Great Lakes system

University Of Rochester, Rochester NY

Investigators

Abstract

In this project the source of methane from the North American Great lakes to the atmosphere will be estimated. Three ship excursions into all five lakes are planned. Methane levels and physical and biological properties will be measured in the surface water. These data will be combined with earlier measurements to capture water-to-air methane transfer from the whole Great Lakes system. Machine Learning will be used to predict methane fluxes from physical and biological properties, many of which are observable from space using satellites. The amount of methane leaking into Lake Erie from natural seeps and gas and oil wells will also be estimated from its radiocarbon content. The proposed work will combine new and existing datasets to estimate diffusive methane emissions from the North American Great Lakes – the largest liquid freshwater system on Earth. This will provide a critical test for models that are used to estimate global freshwater methane emissions, which may significantly overestimate emissions from large lakes. This project will make high-resolution measurements of dissolved methane in surface waters of all five Great Lakes on three proposed research cruises using a novel underway system. The new measurements will be merged with existing data collected using a similar system on previous cruises, yielding a combined methane dataset that captures the seasonal cycle and potential flux hotspots associated with river discharge, natural seeps, and gas wells. Machine learning models will be trained with this data to map methane disequilibrium between the lake surface and air, allowing the lake-atmosphere methane flux to be calculated at high resolution. Researchers will also conduct incubation experiments and stable isotope analyses to construct mixed layer methane budgets for each Great Lake and employ radiocarbon fingerprinting to trace the contribution of fossil methane through the Lake Erie water column. These analyses will allow researchers to distinguish the roles of in situ aerobic methanogenesis, leakage from oil and gas wells, and other external methane sources in driving methane emissions from the Great Lakes. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.