UC Merced

Methane (CH4) is the second most important greenhouse gas after CO2 contributing to climate change. Some ecosystems, such as high-elevation lakes, have been overlooked in their contribution to the CH4 budget and require additional study as they may be disproportionately affected by climate change via increases in average temperatures and changes in seasonal variability. Through extensive sampling and experimentation, this research examined how environmental variation influenced microbial CH4 production and oxidation in the surface waters of high-elevation lakes in the Sierra Nevada, and identified potential sources of aerobic CH4 production. Main findings include that seasonality in CH4 concentrations and fluxes is substantial in freshwater lakes such that predicted increases in temperature, and changes in nutrient loading and dissolved organic carbon may affect overall CH4 emissions from high-elevation lakes. Aerobic CH4 production was carried out in its majority by members of the Comamonadaceae family through the lysis of the C-P bond of methyl phosphonate and through a new potential mechanism by Proteobacteria and Cyanobacteria during (bacterio)chlorophyll metabolism. Moreover, these potential aerobic CH4 mechanisms can be sensitive to warming as shown by the upregulation of functional genes involved in these processes, but the magnitude of the response varied among experiments which suggests that warming alone cannot explain disparities in aerobic CH4 cycling. Overall, these results indicate that CH4 cycling in high-elevation lakes is highly dynamic and heavily influenced by environmental variations, which highlights the importance of further studying these lake ecosystems as our planet changes.