Tuesday, June 5, 2007
442

Denitrification Potential along a Nitrate gradient within Mink Creek

Christopher P. Wilhelm1, Amy M. Marcarelli2, Colden V. Baxter3, and Richard S. Inouye2. (1) Center for Ecological Research and Education, Idaho State University, Department of Biological Sciences, Pocatello, ID 83209, (2) Center for Ecological Research and Education, Idaho State University, Department of Biological Sciences, Pocatello, ID 83209-8007, (3) Stream Ecology Center, Department of Biological Sciences, Idaho State University, Box 8007, Pocatello, ID 83209

We measured denitrification potential in lower Mink Creek, a stream in southeast Idaho with a down-stream gradient of NO3-N (0.1 - 0.5 mg/L) believed to be caused by septic system contamination. Denitrification potential (mg N m-2 s-1) and a modified nutrient spiraling metric, denitrification length (Sw,dn), were used to assess the removal of N by denitrification at two sites, one above the elevated N concentrations (Cherry) and one in the region with elevated N concentration (T4).  Limitations to denitrification potential were assessed using C (C6H12O6), N (NaNO3), and N + C amendments.  Ambient denitrification potential was 0 mg N m-2 s-1 at Cherry and 2.3 mg N m-2 s-1 at T4.  Ambient Sw,dn was 0 km at Cherry and 71.4 km at T4.  Nutrient amendment responses were site specific. At Cherry, there were significant responses to all amendments, while at T4 there were significant responses only to C. Our results show that denitrification in the N-enriched portion of Mink Creek is high and not N limited. However, due to the high ambient N concentrations at this site, denitrification does not appear to be removing a large proportion of the N load in the stream reach with higher nitrate concentrations.

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