Changes in High Elevation Lake Ecosystems of the Sierra Nevada during the 20th Century: Combining Long-term Monitoring with Paleolimnology

Monday, 15 December 2014
James O Sickman1, Andrea M Heard2, Neil L Rose3, Danuta M Bennett4, Delores M Lucero1, John M. Melack5 and Jason H Curtis6, (1)University of California Riverside, Riverside, CA, United States, (2)Sequoia and Kings Canyon National Parks, Three Rivers, United States, (3)University College London, London, United Kingdom, (4)University of California, Santa Barbara, CA, United States, (5)University of California Santa Barbara, Santa Barbara, CA, United States, (6)University of Florida, Gainesville, United States
High mountain lakes of the Sierra Nevada are excellent indicators of anthropogenic global change due to their limited capacity to buffer acid deposition, their sensitivity to changes in snowpack dynamics and their oligotrophic nutrient status. In this presentation, we examine long-term records of hydrochemistry and biological monitoring at the Emerald Lake watershed to assess whether high elevation lakes of the Sierra Nevada are changing in response to climate change or changes in atmospheric deposition of nutrients and acid. To provide a broader context for these changes, we augment these long-term records with results from paleolimnological analysis that examines changes in nutrient status and acid buffering capacity of Sierra Nevada lakes over the past two millennia. Our research suggests that, although atmospheric deposition is the dominant driver of twentieth century ANC trends, aquatic communities in the Sierra Nevada are responding to combined effects from acidification, climate change, and eutrophication. Early in the twentieth century the primary stressor effecting Sierra Nevada lakes was acid deposition driven by SO2 emissions. As the century and industrialization progressed, NOx levels increased adding a eutrophication stressor while simultaneously contributing to acidification. Effects were further complicated by a warming climate in the late twentieth century, as warmer temperatures may have contributed to the recovery of ANC in lakes via increased weathering rates, while simultaneously enhancing eutrophication effects.