Wednesday, June 6, 2007 - 5:00 PM
325

Nitrous Oxide Production Via Denitrification in 71 Headwater Streams Measured with Stable Isotope Additions

Jake J. Beaulieu1, Walter K. Dodds2, Nancy B. Grimm3, Robert O. Hall4, Stephen K. Hamilton5, William H. McDowell6, Patrick J. Mulholland7, Bruce J. Peterson8, Jennifer L. Tank1, H. Maurice Valett9, Jackson R. Webster10, Clay Arango1, Melody J. Bernot11, Amy J. Burgin12, Chelsea Crenshaw13, Bobbie Niederlehner9, Jonathan M. O'Brien14, Jody D. Potter6, Richard W. Sheibley3, Daniel J. Sobota15, and Suzanne M. Thomas8. (1) Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556, (2) Division of Biology, Kansas State University, 116 Ackert Hall, Manhattan, KS 66506, (3) School of Life Sciences, Arizona State University, Tempe, AZ 85287, (4) Department of Zoology and Physiology, University of Wyoming, Laramie, WY 82071, (5) Kellogg Biological Station, 3700 East Gull Lake Drive, Hickory Corners, MI 49060, (6) Department of Natural Resources, University of New Hampshire, Durham, NH 03824, (7) Environmental Sciences Division, Oak Ridge National Laboratory, Bethel Valley Road, PO Box 2008, Oak Ridge, TN 37831-6036, (8) Ecosystems Center, Marine Biological Laboratory, Woods Hole, MA 02543, (9) Department of Biological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, (10) Department of Biological Sciences, Virginia Tech, 2119 Derring Hall, Blacksburg, VA 24061, (11) Department of Biological Sciences, Murray State University, Murray, KY 42071, (12) Kellogg Biological Station and Michigan State University, 3700 Gull Lake Dr., Hickory Corners, MI 49060, (13) Department of Biology, University of New Mexico, Albuquerque, NM 87131, (14) Kellogg Biological Station, Michigan State University, 3700 East Gull Lake Drive, Hickory Corners, MI 49060, (15) Department of Fisheries and Wildlife, Oregon State University, 104 Nash Hall, Corvallis, OR 97331

The production of nitrous oxide (N2O) in streams is of interest because N2O is a potent greenhouse gas and atmospheric concentrations are currently increasing.  As part of the LINX II project we measured N2O emission rates and the relative production of N2O and N2 via denitrification in 71 streams using whole stream isotopic tracer (15N) additions.  Most streams were supersaturated with N2O with a mean emission rate of 4.99 ng N cm-2 hr-1 The best predictor of emission rates was stream nitrate concentrations (r2=0.20, p<0.001).  N2O production via denitrification was detectable in 56 streams and ranged from 0.004-9.2 ng N cm-2 hr-1 (mean 0.86 ng N cm-2 hr-1) and was also positively related to nitrate concentrations (r2=0.66, p<0.001).  N2O production ranged from 0.02-5.8% (median 0.58%) of N2 production and was also positively related to nitrate concentrations (r2=0.27, p<0.001).  On average, N2O produced via in-stream denitrification accounted for 26% of whole-stream N2O emissions, but was highly variable across the 56 sites where it was measurable, ranging from 0-100%.  These data demonstrate that headwater streams can function as a source of N2O to the atmosphere and that nitrate concentration is a key driver of in-stream N2O dynamics.

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