Wednesday, June 6, 2007 - 4:15 PM
322

The Contribution of Nitrogen Fixation to Nitrogen Cycling in Ditch Creek, WY Throughout the Summer Season

Lisa A. Kunza, Program in Ecology, Department of Zoology and Physiology, University of Wyoming, Laramie, WY 82071 and Robert O. Hall Jr., Department of Zoology and Physiology, University of Wyoming, Laramie, WY 82071.

Nitrogen (N) fixation is among the least studied processes of the N cycle in streams, despite its potentially dominant role in N-limited systems.  Many streams in NW Wyoming are N limited.  We hypothesize that N-fixation contributes to the N budgets of some streams.  Cyanobacteria control the extent to which N uptake or transport occurs and may be important suppliers of N to downstream areas within these watersheds.  To assess the importance of N-fixation to a stream N budget, we measured stream N fluxes throughout the summer season for Ditch Creek which is located in Grand Teton National Park, WY.  Ditch Creek had high N-fixation rates (2.53 mg N m-2 hr-1) measured in summer 2005.  We measured N-fixation regularly from June 2006 through September 2006 using the acetylene-reduction technique.   N-fixation was low (0.77mg N m-2 hr-1) in June, and peaked in late July at 4.06mg N m-2 hr-1.  N-fixation rates declined throughout the remainder of the summer until our last measurement in September (0.59mg N m-2 hr-1).  Nitrogen fixation rates throughout the summer season were 10 to 100 times greater than uptake rates.

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