PARENT SESSION
Poster Session 6: Arctic and Alpine Ecology
Tuesday, August 9, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Patterns of Change in the Green Lakes Valley Phytoplankton Communities.

Roche, Amber ^{*,1, 2}, McKnight, Diane ^{*,1, 2}, Flanagan, Colleen¹, Gardner, Eileen¹, ¹ Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO² Niwot Ridge Long Term Ecological Research Project, Boulder, CO

ABSTRACT- Spatial and temporal monitoring of phytoplankton communities in an alpine lake in the Green Lakes Valley, Colorado, indicates that the ecosystem responds to interannual variation in hydrologic regime. The Green Lakes Valley, located along the Front Range of the Rocky Mountains, is part of the Niwot Ridge Long Term Ecological Research (LTER) site and contains several alpine and subalpine lakes. Species composition data at various depths has been compiled over the summers (June-August) of 5 years (2000-2004) and then integrated with hydrological, climatic, and experimental data. Statistical analysis (PCA) indicates a progressive change in the algal species composition during each summer, and even greater population shifts among summers. Our results show the algal communities throughout the water column during the drought year (2002) were dramatically different from communities in previous and subsequent years. Chlorophyta and Cyanophyta underwent the most significant changes. This response suggests that the ecosystem is highly sensitive to changes in physical conditions in the lake, such as flushing rate. Separation was also observed between years of similar climate patterns suggesting the influence of additional factors affecting these communities. One such factor could be nutrient limitation of algal productivity; experimental data shows that an increase in nitrogen input as a result of anthropogenic deposition can cause similar shifts in the phytoplankton community. These observed trends are not only important for the health of the watershed but can provide insight into the impact of climate change on lakes elsewhere.

Key words: phytoplankton, lakes, climate, alpine