Date of Award

12-2016

Level of Access

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ecology and Environmental Sciences

Advisor

Jasmine E. Saros

Second Committee Member

Hamish Greig

Third Committee Member

Michael Kinnison

Additional Committee Members

Zoe Finkel

Lee Karp Boss

Abstract

In many lakes across arctic, alpine, boreal and temperate regions of the Northern Hemisphere, paleolimnological records have revealed that the relative abundances of the centric diatom Cyclotella sensu lato taxa have changed over the past century. Cyclotella sensu lato taxa are a key group of diatoms that are very sensitive to environmental change and may serve as early indicators of ecosystem effects of global change. Yet patterns of change in Cyclotella species are not synchronous across, or even within, regions, raising the question of mechanisms behind these widespread changes in diatom community structure. Changes in Cyclotella taxa have been attributed to an indirect link with temperature-driven changes in lake thermal stratification, specifically in terms of changes in water column stability that lead to altered light penetration and nutrient availability. In the first chapter, I conducted experiments to test the effects of temperature, light, and nutrients on Lindavia intermedia, Lindavia radiosa, Lindavia comensis, Lindavia ocellata and Discostella stelligera. I found that interactive effects of temperature, light, and nutrients affected all the species except L. radiosa. Responses to these factors varied across taxa. For example, when nutrients were provided, L. radiosa was more abundant under high light conditions, whereas L. ocellata was more abundant under low light conditions. I also determined whether different phytoplankton communities (one dominated by diatoms and the other by a mixed assemblage) altered the response of D. stelligera to abiotic factors. High temperature, light and nutrients only increased cell densities of D. stelligera when this species occurred in the diatom- dominated community. In the second chapter, to further understand the mechanisms behind these species changes, I investigated how the nutrient limitation status of a lake alters the responses of three common Cyclotella sensu lato taxa to light. I found that light affected Cyclotella growth rates, cell densities, and distribution patterns differently depending on lake nutrient limitation status. Lindavia intermedia fared best at low light under P-limitation, and at high light under N&P co- limitation, while the pattern was generally opposite for D. stelligera. For L. radiosa, regardless of nutrient limitation status, moderate to high light was important for this species. In the third chapter, I investigated how a difference in the timing of ice off affected Cyclotella cell densities over the ice-free season. I found that L. intermedia cell densities were abundant in deep waters in late summer during the early ice off year (2012), whereas the abundance of D. stelligera was greater during the later ice off year (2015) and was uniformally distributed in the water column. My study provides further ecological insight into Cyclotella species that serve as important indicators of environmental change. My study reveals that environmental change affects these species via complex interactions between nutrient and light availability, and helps to clarify some of the complex distribution patterns of planktonic diatom taxa found in lakes of many areas around the Arctic as well as at lower latitudes.

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