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Jennifer Lynn Klug

Advisor: Tony Ives

PhD Abstract: Complex effects of colored dissolved organic matter on algal growth and community composition.

Colored dissolved organic matter (CDOM) is a mixture of organic compunds that give brown water lakes their characteristic color. Common constituents of CDOM include organic acids such as humic and fulvic acids. CDOM may affect algal growth in several ways. A major negative effect is the reduction of algal growth by shading from absorbance of light by CDOM. In addition, CDOM may change the availability of inorganic nutrients directly, since it contains nitrogen and phosphorus. CDOM may also affect nutrient availability indirectly by stimulating bacterial growth, which in turn may change the availability of nitrogen, phosphorus, and carbon. This dissertation explores the complex effects of CDOM on algae in several ways. In Chapters 1 and 2, I describe results from short-term experiments conducted with phytoplankton from West Long Lake. Chapter 1 contains experiments designed to descern between the positive and negative effects of CDOM on algae. Results from Chapter 1 suggest that positive effects of CDOM may outweigh negative effects for nutrient limited phytoplankton if CDOM contains nutrients which are available to phytoplankton. Chapter 2 contains experiments and a model designed to test whether interactions between algae and bacteria affect algal response to CDOM. Experimental results showed that the effect of CDOM on algal growth depended on the amount of phosphorus sequestered by bacteria, suggesting strong competition between algae and bacteria. Chapter 3 investigates the effects of changes in nutrient loading and CDOM on the dynamics of phytoplankton communities in two basins of Long Lake over a 7 year period. Results suggest that there was an interaction between the effects of CDOM and nutrients for many groups of phytoplankton, such that differences in CDOM concentration accounted for differences between basins in response to nutrient addition.

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