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Olivier, Matthew R ¹

¹ INSTAAR

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 a mesocosm experiment was conducted using cattle tanks at the Niwot Ridge Long Term Ecological Research Site (NWTLTER) in the Colorado Front Range. 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. Preliminary results of the mesocosm experiment seem to suggest that the temperature treatment, the nitrogen additions and combinations of both treatments had no significant impacts on the community composition of the algal communities in the mesocosm. Our PARAFAC results indicate that the majority of the DOM in the tanks is terrestrial in origin with fluorescence index (FI) vales ranging from just over 1.5 to just below 1.3. In the mesocosms were the temperature was not increased there is a negative trend through time in FI across all nitrogen treatments.