Date of Award

4-2018

Degree Name

Master of Science

Department

Biological Sciences

First Advisor

Kathryn M. Docherty, Ph.D

Second Advisor

Carla M. Koretsky, Ph.D

Third Advisor

Steve Kohler, Ph.D

Access Setting

Masters Thesis-Abstract Only

Restricted to Campus until

4-15-2028

Abstract

The use of road salt deicers is increasing in northern regions that experience icy winters. Saline runoff can enter bodies of freshwater such as lakes and change the geochemistry within the water column by interfering with seasonal turnover and extending periods of hypolimnetic anoxia. This extended anoxia can cause shifts in the location of various taxa. In this study, we examined the vertical microbial community profiles of three lakes with different mixing regimes in southwest Michigan. We took samples during all four seasons, and compared community composition with geochemical and physical parameters related to stratification. The communities of all three lakes differed from each other, and within each lake the oxic zone, anoxic zone, and sediment communities were also significantly different. Differences between the lakes increased with depth; sediment communities were the most endemic to each lake, while oxic zone communities were the most similar across lakes. Seasonal changes in lake oxygen stratification resulted in seasonal differences in microbial community structure, including several functional groups of taxa related to carbon and nitrogen cycling, within each lake. Sediment methanogen relative abundances and methane production were highest in the meromictic lake and lowest in the dimictic lake, suggesting that road salt inputs which impact stratification can result in increases in greenhouse gas production through microbially-mediated processes.

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