Investigating potential effects of the agricultural contaminants nitrogen and copper on high-elevation lake ecosystems in Sequoia National Park, California
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Benthic algae blooms in remote mountain lakes are an emerging concern, but there are many questions regarding what factors influence this phenomenon. In Sequoia National Park in the Sierra Nevada mountains of California, previous research has shown that atmospheric deposition of the macronutrient nitrogen can increase algae growth. Drift modeling also indicates that this region likely receives deposition of copper, a micronutrient, from nearby agricultural pesticide use. As such, we designed a series of studies in the Tokopah Basin with the following objectives: 1) quantify concentrations of nitrogen and copper in high elevation lakes, and evaluate relationships with landscape variables and periphyton growth metrics, 2) investigate the potential for nitrogen and copper to fuel periphyton growth and modify community structure using an in-situ experiment, and 3) evaluate interactions of copper with Pacific chorus frog (Pseudacris regilla) tadpole development. We observed spatiotemporal trends in nitrogen and copper concentrations in lake media, but no detectable effect of these elements on periphyton growth. However, our in situ experimental study revealed that greater copper concentrations reduced periphyton growth and diversity, and that nitrogen and copper worked interactively to alter the algae community. Finally, we found that copper concentrations in tadpoles declined as they developed. This research provides baseline copper concentration and periphyton growth data for future studies, evidence that high nitrogen and low copper concentrations can promote the abundance of specific benthic algae taxa of concern, and evidence that developing tadpoles are unlikely to accumulate and transport copper from aquatic to terrestrial ecosystems.
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Ph. D.