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Flanagan, Colleen MÌý¹Ìý;ÌýMcKnight, Diane MÌý²Ìý;ÌýRoche, AmberÌý³Ìý;ÌýGardner, EileenÌý⁴Ìý;ÌýMcDougall, SarahÌý⁵

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⁵ÌýPenn State University

Because the hydrologic regime of alpine catchments is dominated by snow melt, these aquatic ecosystems are sensitive to fluctuations in the amount of snow, chemical nature of snow, and timing of snowmelt. The drought of 2002 in Colorado was the most extreme drought of the past 100 years of record for the state. Measured at the outflow of Green Lake 4, an alpine lake in Green Lake Valley, located within the Niwot Ridge Long Term Ecological Research (LTER) site in the Front Range of Colorado, the 2002 drought resulted in snowmelt discharge that was just 60% of recent historical averages for stream discharge. We examined how the drought affected the phytoplankton population in this alpine lake. Algal biomass was quantified, and samples for community composition were analyzed throughout the summers of 2000–2004. Species in two divisions, Bacillariophyta and Chlorophyta, showed significant responses in abundance and distribution. A principal components analysis confirmed a shift in the community composition during the drought. Drought-induced factors such as earlier ice-out and hence higher irradiance, higher hydraulic residence time and lower wash-outs, plus higher surface water temperatures may have driven the change. Although based on only five seasons of monitoring data, these results may foreshadow climate change and implicate subsequent biological effects in high altitude watersheds.

Doesken, Nolen J. and Pielke, Roger A. Sr., 2004, The Drought of 2002 in Colorado, Presented at the 84th AMS Annual Meeting, 14th Conference on Applied Meteorology, Seattle, Washington, 7-16 January.

Gardner, E.M., W.M. Lewis, Jr., D.M. McKnight, 2003, Effects of Nutrient Enrichment on Phytoplankton in an Alpine Lake, Colorado, U.S.A. A thesis submitted to the University of Colorado, Â鶹ӰԺ.

Kolesar, S.E., D.M. McKnight, S.B. Waters, 2002, Late fall phytoplankton dynamics in three lakes, Rocky Mountain National Park: Hydrobiologia, v. 472 (1-3), p. 249-263.

NWT-LTER Database. .

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