Collaborative Research: Consequences of changing oxygen availability for carbon cycling in freshwater ecosystems

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The amount of oxygen in many lakes and reservoirs is changing globally. These changes may threaten ecosystem services lakes provide. In addition to degrading drinking water and fisheries, changes in oxygen can change how much carbon is buried in lake bottoms. Since human-made reservoirs store more carbon annually than the ocean, these changes may have a major impact on global carbon cycling. The magnitude of changes in oxygen, and consequences for water quality, are unknown. This project will take advantage of an unprecedented opportunity to switch an entire reservoir from low to high oxygen. The study includes several experiments that involve changing oxygen levels, and examining the impacts on carbon cycling. This research will improve predictions of how environmental changes will affect carbon burial in lakes. The project results will help managers meet goals to improve reservoir water quality. It will also contribute to understanding long-term effects of management on carbon burial in lakes. This project will produce educational tools and lesson plans for undergraduate courses on reservoir ecology. Project scientists will work with water utilities and the broader research community to share knowledge to improve policy. Finally, graduate and undergraduate students will be trained in subjects spanning ecology, geosciences, and engineering. Freshwaters, especially human-made reservoirs, receive and process a vast amount of carbon, which can be emitted as carbon dioxide and methane or buried in sediments. Increasingly variable oxygen concentrations may have global implications for freshwater carbon cycling because high oxygen conditions promote not only the mineralization of new carbon that has recently entered an ecosystem, but also legacy carbon accumulated over years of sedimentation. This project will address the overarching question: How will changes in oxygen alter carbon processing and carbon dioxide and methane emissions in freshwater ecosystems? To answer these questions, carbon mineralization and electron acceptor pathways will be measured with new sensor technology at the time scale of minutes under different oxygen and temperature conditions in whole-ecosystem oxygen experiments to quantify rates of carbon processing. Additional sampling across a suite of reservoirs on a gradient of oxygen availability will be used in open-source ecosystem models to improve predictions of long-term carbon burial in freshwater ecosystems. In sum, integrating whole-ecosystem manipulations of oxygen with modeling will determine how dynamic oxygen conditions alter carbon cycling in aquatic 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.