Impacts of Dry Atmospheric Deposition on Aquatic Systems - Nutrients, Trace Metals and Lead Isotopes
Atmospheric deposition is a source of new N, P and trace metals to the ocean and water bodies on land. Nutrient and trace metal inputs from atmospheric deposition have been shown to induce phytoplankton growth and impact water chemistry. The three chapters presented in this thesis examine dry atmospheric deposition impacts on phytoplankton and water chemistry including: (1) How African dust impact phytoplankton growth at the low nutrient low chlorophyll (LNLC) ocean off Barbados; (2) Evaluate the contribution of Pb from Asian dust to the western Philippine Sea, and (3) Evaluate the contributions of nutrients and trace metals from aerosol to Lake Tahoe. In the first study, a bioassay incubation experiment conducted with nutrients and local atmospheric aerosol amendments indicates that phosphorus (P) availability limited phytoplankton growth in the low nutrient low chlorophyll (LNLC) ocean off Barbados. The results also suggest that atmospheric deposition induces P limitation in this LNLC region by adding more N and iron (Fe) relative to P. This favors the growths of Prochlorococcus, a genus characterized by low P requirements and highly efficient P acquisition mechanisms. In the second study, the dissolved lead (Pb) concentrations and isotopic compositions in seawater of the western Philippine Sea (WPS) were determined to investigate sources and sinks of Pb. The results suggest sedimentary inputs are a major source of dissolved Pb in deep water and Asian aerosols in surface water. Differences in Pb concentrations and isotopic signatures between water samples collected from the Pacific Deep Water water-mass during this study and those collected a decade ago suggest that the anthropogenic input of Pb changes even in deep water on decadal scales. In the third study, the trace metal concentrations and Pb isotopic composition in aerosols and in lake water were determined. The results show a seasonal trend of trace metal concentrations and solubilities. Pb isotopes indicate atmospheric deposition is not a major source of Pb to the lake, or that the turn-over rate of lake water is faster than the Pb residence time.