Date of Award

12-2013

Level of Access Assigned by Author

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ecology and Environmental Sciences

Advisor

Jasmine Saros

Second Committee Member

Ivan Fernandez

Third Committee Member

Brian McGill

Abstract

Climate change is expected to have profound effects on boreal lakes; however, the nature and magnitude of these effects across broad spatial and temporal scales is poorly understood. Here, I used neo- and paleo-limnological tools to decipher the extent to which climate-mediated changes in energy (irradiance, heat, and wind) or mass (water, suspended particles, and dissolved substances) are contributing to broad changes in boreal lakes. I selected lakes in two regions of boreal forest in the United States that are experiencing changes in either energy (air temperature and wind changes in Isle Royale National Park (ISRO) in the Upper Midwest) or mass (changes in the amount and chemical characteristics of precipitation in the Northeast). To assess long-term variability in lake response to changes in heat and wind in ISRO, high frequency monitoring of lake temperature was paired with paleolimnological analyses of diatom- inferred mixing depth and fossil algal pigments in two lakes in ISRO during the 20th century. To determine the effects of extreme weather on surface water chemistry in the northeastern U.S., a 30-year database of surface water geochemistry for 84 lakes was combined with newly developed landscape data and watershed-specific weather data to model lake chemical response during an extreme wet and an extreme dry year as a function of watershed features. A separate dataset that included lakes in Acadia National Park in Maine and the Pocono Mountains in Pennsylvania was used to evaluate water clarity as a sentinel of environmental changes that modified mass influx across the region.

Broad patterns in lake response to climate were consistent with expected changes in both regions; however, the magnitude of change was dependent on watershed and lake- specific characteristics. Lake mixing depth deepened as wind strength increased in ISRO. This had a greater effect on physical lake habitat in the shallower and more productive lake. Episodic changes in lake chemistry occurred in response to extreme weather in the northeastern U.S. Episodic acidification was observed during drought and episodic brownification was observed during wet years. This change may be contributing to accelerated recovery from acidification and reduced water clarity in recent decades.

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