Date of Award

5-2011

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Ecology and Environmental Sciences

Advisor

Jasmine E. Saros

Second Committee Member

Aria Amirbahman

Third Committee Member

Kevin Simon

Abstract

Boreal lake ecosystems in the U.S. have experienced enhanced nitrogen (N) deposition and increasing dissolved organic carbon concentrations. These changes can lead to N enrichment as well as affect water transparency and nutrient influx. To investigate the combined effects of N enrichment and changing DOM influx on phytoplankton in boreal lakes, we conducted a series of experiments in which we established a gradient of N concentrations, and tested the shading versus nutrient addition effects of DOM additions in a factorial design with the N gradient. Experiments were conducted in two lakes, one N limited and one N&P co-limited, both N&P additions are required to observe phytoplankton growth. As expected, N additions increased chlorophyll concentrations in the N limited lake, but not the N&P co-limited lake. While the shading effects of DOM did not alter chlorophyll concentrations, the nutrient enrichment effects of DOM strongly stimulated phytoplankton growth in both lakes, with chlorophyll concentrations more than double those in control treatments. Our results suggest that DOM influx will have widespread effects on phytoplankton biomass across boreal lakes and increases in atmospheric N deposition will only affect N-limited boreal lake ecosystems.

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