Changes in Diatom Taxa in Sierra Nevada Lakes during the 20th Century:
Implications for Critical Loads Development

Dr. James O. Sickman1*, Dr. Danuta Bennett2, Andrea Heard1 and Delores Lucero

The main objective of our study is to establish critical loads for nitrogen deposition in aquatic ecosystems of the Sierra Nevada, using reconstructions of past lake chemistry based on diatoms preserved in lake sediments. Using diatom and water quality data from an extensive survey of highelevation lakes, we are developing diatom-based models of past nutrient and trophic conditions and applying these models to sediment cores collected from two high elevations, Moat Lake (Hoover Wilderness) and Hamilton Lake (Sequoia National Park). We will present initial water quality models derived from the lake survey, describe changes and trends in diatom flora over the past 100 years and discuss these findings in the context of critical loads development.

1* Email: , Phone (951) 827-4552
1 Department of Environmental Sciences, University of California, Riverside, CA 92521
2 Marine Science Institute, University of California, Santa Barbara CA 93106,