External drivers of limnetic bacterial community composition and function

Bacteria are key components of biogeochemical processes that occur in lakes, and therefore we seek to understand factors that determine their community composition and function. A large majority of efforts to describe bacterial community dynamics has focused on chemical and biological drivers that originate within the lake. In this dissertation I attempt to characterize three factors originating outside the lakeshore (extrinsic factors) that structure lake bacterial community composition.;Extreme weather events can drive rapid change in the physical structure of the water column of a lake. I explored the influence of typhoons on the physical structure and microbial community dynamics of Yuan Yang Lake, Taiwan. Following typhoon-induced mixis, restratification of the water column occurred rapidly and drove surprisingly repeatable patterns of bacterial community succession.;Long distance atmospheric transport of bacterial cells is often cited as an explanation for the apparent cosmopolitan distribution of bacterial taxa. Surprisingly, efforts to measure immigration in bacterial communities are rare. I captured atmospherically deposited cells over two summer seasons, and found little overlap of bacterial taxonomic composition of 16S rRNA gene sequence databases from lakes and the atmosphere.;Transport of terrestrial organic carbon into lakes has become a key area of study within limnology over the last decade. As the primary users of dissolved organic carbon, bacteria can meet a large portion of their energy and nutrient demand using terrestrial-derived organic matter. I conducted a survey of bacterial 16S rRNA gene composition in fifteen lakes positioned along a color (absorbance at 440 nm) : chlorophyll a gradient. My survey supported the hypothesis that bacterial populations partition along a carbon substrate source gradient and suggests hypothetical carbon source-bacterial interactions that should be explored further.;Stable isotope tracers have been extremely useful in estimating the relative contribution of terrestrial- and aquatic-derived carbon used in aquatic secondary production. However, methods for estimating carbon stable isotope ratios in bacterial biomass or biomarkers are still under development. I attempted to develop a method combining fluorescent activated cell sorting, spooling wire micro-combustion, and isotope ratio mass spectrometry for estimation of carbon stable isotope ratios in bacterial biomass.