The iconic Yosemite National Park (YNP) extends from the foothills of California’s Sierra Nevada Mountains to their 4,000 m crest, encompassing >3,000 km2 and hosting ca. 5 million visitors annually. Within its boundaries, YNP protects many unique organisms and ecosystems, including river systems that supply drinking water and irrigation water to California’s millions of citizens and multibillion dollar agricultural industry. Our research is focused on the microbial ecology of high mountain lakes—which form part of this freshwater network, and are also a naturally beautiful highlight of Yosemite.
However, YNP is located upstream and downwind from the Central Valley of California, an intensive agricultural area that suffers poor air quality and presents a stark contrast—with feedlots, factories, and freeways located ~100 km from the Sierra. As a consequence, the National Park Service is concerned about transport of atmospheric pollutants into YNP (http://www.nps.gov/yose/naturescience/airquality.htm). High elevations are also rapidly warming, and lakes are considered climate ‘sentinels’ that are sensitive to rising temperatures (Williamson et al. 2009 and references therein). Changes in carbon fluxes into and out of lakes are a major concern, as lakes are carbon ‘sinks’ that effectively ‘store’ material that is transported into them from surrounding watersheds.
We began sampling along a lake elevation gradient in YNP in 2010, examining multiple aspects of lake biogeochemistry and microbial ecology on a regular basis. We published our work on nitrogen cycling in 2014 (Hayden and Beman 2014, PLOS ONE) and found relatively little evidence for the influence of atmospheric nitrogen deposition. Our work on lake microbial community ecology was published in 2015 (Hayden and Beman 2015, Environmental Microbiology). One interesting aspect of this research was finding high abundances of methane (CH4)-cycling organisms in our sequence data, as CH4 is an important greenhouse gas. Lakes are a large natural source of CH4 to the atmosphere, but our understanding of lake CH4 cycling—and global sources of CH4 in general—is poor.
As a result, our current focus is on CH4 production and consumption in these lakes. We received a Joint Genome Institute Community Science Program in early 2015, and are conducing metagenomic analysis of the microbial communities involved in CH4 cycling in high altitude lakes. We are also quantifying rates of CH4 production and consumption, and determining the sensitivity of these processes to different forms of environmental change. Work by Ph.D. student Eli Perez-Coronel shows clear evidence for CH4 production in high elevation lakes, and implicates multiple biological processes.
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Mike is also a co-PI for the Yosemite REU program funded by NSF. Contact him if you are undergraduate interested in summer research in the Park.
REU program and press release: