RAPID: Quantifying the response of oxic methane production to biogeochemical changes in aquatic ecosystems: record Sierra Nevada snowmelt as a natural experiment

Methane is a fascinating gas that can be burned in appliances and rockets, yet also acts as a powerful greenhouse gas in the atmosphere. A wide range of biological and geological processes produce methane, making it challenging to figure out how methane moves between land, water, organisms, and the atmosphere. Some of these processes have been altered by human activity, leading to increasing methane concentrations in the atmosphere that contribute to climate change. However, recent discoveries have made things even more complicated by showing that methane is produced unexpectedly in surface waters of lakes and the ocean. How and why this occurs is still not fully understood, but it may be linked to the supply of nutrients and carbon to aquatic ecosystems. This research project addresses the role of nutrients and carbon in methane production by using a natural experiment provided by record snowpack in California’s Sierra Nevada mountains. As snow melts and eventually enters high elevation freshwater lakes, it can bring nutrients and carbon with it. Researchers will determine whether this influx of nutrients and carbon leads to oxic methane production by tiny organisms living in these lakes. The researchers are regularly sampling five lakes spread across the higher elevations of Yosemite National Park in California. These lakes typically show a peak in methane concentrations and production in late summer or early fall, and these peaks are hypothesized to be particularly high following increased snowpack and snow melt. The researchers will determine which mechanisms and organisms produce methane, and how they are affected by nutrients and carbon, through a combination of biogeochemical measurements and techniques from molecular biology applied to samples collected in the lakes and lab-based experiments. The research will determine (1) whether oxic methane production is affected by nutrients and carbon, (2) which processes produce methane, and (3) how processes may change due to natural or human-caused changes in nutrient and carbon fluxes. 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.