EAGER: Discovering how geologic and fossil methane sources support a contemporary river ecosystem

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Carbon is a fundamental building block of life. For most animals (insects, fish, plankton) in streams and lakes the carbon starts out as carbon dioxide and then is captured by algae and plants. This carbon then passes on to plankton, insects, and fish. Recent studies suggest there might be other sources of carbon in rivers such as methane that are supporting aquatic plants and algae. However, little is known about the sources of this methane and how it gets incorporated into the life in rivers, streams, and lakes. Methane may be released to groundwater and streams in areas with high geologic or geothermal activity. This EAGER award will conduct the first study to explore the role of geologic and fossil methane as an alternative carbon source in supporting life in river floodplains. The award will also support research training of students and doctoral scholars, engage fish hatchery managers in citizen science research, and provide knowledge of how river systems function to the public. The underlying assumption for most ecosystems on Earth is that the fixation of modern carbon dioxide drives productivity and biodiversity, with little recognition or study of other potential carbon pathways (e.g., methane) as drivers of productivity and biodiversity. Despite the likely contribution of fossil and geologic methane to freshwater systems and the potential for methane to be transformed ecologically into less harmful forms, the freshwater biotic processes affecting this greenhouse gas source are poorly known. This EAGER award will investigate the role of abiotic, thermogenic, and fossil methanogenic methane subsidies in supporting freshwater floodplain ecosystems by providing a carbon source to the carbon-limited shallow aquifer food web (deep hyporheic zone). The objective of this award is to quantify contributions of carbon from various methane sources to the aquifer food web. Innovative stable isotope methods will be used to assess the carbon sources and trace them through the floodplain foodweb, then develop new approaches for discovering methane source contributions to freshwater ecosystems. This research could potentially shift the current carbon dioxide-based paradigm of driving productivity and biodiversity by demonstrating that shallow aquifer food webs below river floodplains are driven by geologic and fossil methane-derived carbon. Therefore, these floodplain aquifers would be the first to demonstrate a conceptually and ecologically analogous paradigm to oceanic hydrothermal vent ecosystems.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.