Flanagan, Colleen MÌý1Ìý;ÌýMcKnight, Diane MÌý2Ìý;ÌýRoche, AmberÌý3Ìý;ÌýGardner, Eileen MÌý4Ìý;ÌýWeber, Lindsay RÌý5
5ÌýPresenting Author
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Because the hydrologic regime of alpine catchments is dominated by snow melt, these aquatic ecosystems are sensitive to fluctuations in the amount of snow, the chemical nature of snow, and timing of snowmelt. Investigations of an alpine step lake, Green Lake 4, located in the Niwot Ridge Long Term Ecological Research (NWTLTER) site in the Front Range of Colorado, have shown that earlier, warmer springs, thinner ice cover, and increased atmospheric nitrogen deposition have occurred over the past 20 years. In context of the 2002 drought, the lowest discharge on record, I examined how these environmental processes drive the variability of the phytoplankton population based upon NWTLTER climate data from the 1981–2005. Throughout the summers of 2000–2005, algal biomass was quantified, samples for community composition were analyzed, and the water column chemistry was characterized. It was hypothesized that changes in precipitation and temperature would shift the phytoplankton community composition. A Principal Components Analysis (PCA) confirmed taxon-specific shifts in the community composition during the drought of 2002 in Colorado, while a Redundancy Analysis (RDA) depicted the importance of temperature, silica, andÌýSynedraÌýsp. Further, increased phosphate concentrations during the post-drought period shifted the dominance of Chlorophytes, suggesting the influence of nitrogen deposition on P limitation. Although based on only six seasons of monitoring data, including the driest year on record, these results may foreshadow climate change and implicate subsequent biological effects in high altitude watersheds.