Date of Award

Spring 1-1-2017

Document Type

Thesis

Degree Name

Master of Science (MS)

First Advisor

Diane M. McKnight

Second Advisor

Diane M. McKnight

Third Advisor

Pieter Johnson

Fourth Advisor

Patrick Kociolek

Abstract

Much like in the arctic, organisms inhabiting alpine ecosystems are living at the edge of their environmental tolerances, and are thus sensitive to small changes in climate. Algal communities of alpine lakes are particularly useful as indicators of environmental change due to the fact that they are typically diverse and rapidly respond to environmental changes over short time scales. During the summer of 2014, an aquatic mesocosm experiment was conducted using cattle tanks at the Niwot Ridge Long Term Ecological Research Site (NWTLTER) in the Colorado Front Range. The purpose of the experiment was to examine the effects of increased temperature and nitrogen deposition on alpine phytoplankton communities and dissolved organic matter (DOM). Phytoplankton communities from the mesocosms were characterized using Flow Cytometer and Microscope, and the DOM produced in the mesocosms was analyzed using fluorescence spectroscopy and parallel factor analysis (PARAFAC) modeling. The results of the experiment suggest that the temperature treatment, the nitrogen additions, and combinations of both treatments, had no significant effects on the algal communities in the mesocosms. In our experiment, the abundance of Daphnia increased significantly in the low temperature mesocosms, and only slightly in the high temperature mesocosms. The PARAFAC results indicate that the DOM in the mesocosm is terrestrial in origin, with fluorescence index (FI) vales ranging from just over 1.5 to just below 1.3. In the low temperature mesocosms, the FI decreased as the experiment progressed. This decrease in FI in the low temperature mesocosms may be explained by a top-down control by Daphnia on microzooplankton, which feed on the bacteria that consume the DOM that is released by phytoplankton. This likely limited the accumulation of extracellular quinone-containing organic compounds that can contribute to a more microbial FI signal. The top-down control by the Daphnia on the microbial loop could explain the shift in DOM quality, the predominantly terrestrial FI values, and the increased freshness observed in the low temperature mesocosms. It is important to understand the dynamics of DOM in alpine watersheds because DOM is potential precursors for the formation of disinfection byproducts (DBPs) resulting from water treatment practices

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