Date of Award

Spring 1-1-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Geological Sciences

First Advisor

Jason C. Neff

Second Advisor

Gifford H. Miller

Third Advisor

Alexis S. Templeton

Fourth Advisor

Patrick Kociolek

Fifth Advisor

Richard L. Reynolds

Abstract

Human activities have significantly altered the chemistry of the atmosphere, changing the global mobility of key macronutrients. The availability of nitrogen and phosphorus is of particular importance because they are often the most limiting nutrients in many terrestrial and freshwater ecosystems (Vitousek and Howarth 1991, Vitousek et al. 2010). Alpine lakes typically receive a large fraction of their nutrients from atmospheric deposition, thus shifts in deposition rates and composition have the potential to impart changes to aquatic biogeochemistry. Gaseous nitrogen is emitted from industrial and agricultural processes (Galloway et al. 2003), and particulate phosphorus is emitted associated with soil dust and biomass burning emissions (Mahowald et al. 2008). Mineral aerosols associated with dusts also have the potential to neutralize airborne acids and contribute alkalinity to depositional environments (Sequiera 1993). A combination of modern and historical environmental data is used in this thesis to 1) examine dust deposition histories across the western US and 2) examine the effects of the atmospheric deposition of nutrients on alpine lake chemistry and ecology. National scale data on precipitation chemistry revealed large increases in dust emissions over broad regions of the western US. Increased dust emissions were tied to significant increases in precipitation alkalinity and to elevated nutrients in downwind ecosystems. Spatially I found that the global, regional, and local patterns of nutrient emissions and deposition were reflected in the water chemistry of alpine lakes. Lakes in affected areas have altered species communities, and higher levels of nutrients and heavy metal concentrations. Collectively this research has demonstrated the extent to which human activities have influenced aquatic chemistry and nutrient availability and illustrate the sensitivity of alpine lakes to changing atmospheric deposition. Because national scale monitoring networks are not set up to capture dust related nutrient deposition, the scope and impacts of this large-scale biogeochemical perturbation is not well understood. Based on the results presented here, we can expect alpine lake nutrient status to evolve alongside anthropogenic and climate related increases in dust and nitrogen emissions. The sensitivity of all aquatic ecosystems to nutrient inputs emphasizes the need to measure dust and phosphorus deposition in order to better protect our freshwater ecosystems.

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