CS08 Biogeochemical Cycles
Date: Tuesday, June 11, 2002
Location: Poster Session - VCC
 
GardnerEM, University of Colorado, Boulder, USA, eileen.gardner@colorado.edu
Lewis, Jr., W, M, University of Colorado, Boulder, USA, lewis@spot.colorado.edu
McKnight, D, , University of Colorado, Boulder, USA, mcknight@snobear.colorado.edu
 
EFFECTS OF ATMOSPHERIC NITROGEN DEPOSITION ON SEASONAL PHYTOPLANKTON DYNAMICS IN AN ALPINE LAKE, COLORADO, U.S.A.
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Enrichment of aquatic ecosystems with nitrogen may alter seasonal changes in the productivity and composition of phytoplankton communities. The effect of nitrogen deposition on phytoplankton dynamics was investigated in an alpine lake located at the Niwot Ridge LTER site in northern Colorado. Primary production and species composition of phytoplankton were quantified during snowmelt and throughout the summer months. The chemical environment of the water column was characterized in order to interpret changes in algal communities. Samples were analyzed for major ions, pH, acid-neutralizing capacity (ANC), organic and inorganic fractions of nitrogen and phosphorous, and conductivity. Nitrate values were highest following snowmelt, and decreased throughout the summer. ANC and pH were lowest following snowmelt and increased throughout the summer. These results suggest that the majority of excess nitrogen in the system is released in a pulse during snowmelt. Primary production peaked following snowmelt and again in late summer. The rapid increase in nitrogen during snowmelt due to atmospheric nitrogen deposition introduces the potential for alterations in phytoplankton community composition due to changes in the chemical surroundings.