Wednesday, May 28, 2008 - 2:45 PM
432

Biogeochemical response of forested watersheds to wildfire

Lusha M. Tronstad, Department of Renwable Resources, University of Wyoming, 1000 E. University Ave., Laramie, WY 82071, Robert O. Hall, Jr., Department of Zoology and Physiology, University of Wyoming, 1000 E. University Ave., Laramie, WY 92071-3166, Todd M. Koel, Yellowstone National Park, PO Box 168, Yellowstone Park, WY 82190, and Christine F. Keep, Student, 3317 East 14th Street, The Dalles, OR 97058.

Disturbances that kill terrestrial plants can strongly alter cycling of ions within watersheds.  We investigated how wildfire changed stream concentration and export of ions in coniferous watersheds, which may differ from that of (well-studied) deciduous forests.  During fall 2003, wildfire consumed 95% of two watersheds and 40% of one watershed within the Yellowstone Lake drainage, Yellowstone National Park, Wyoming.  We collected water samples serendipitously in summer 2003 prior to the wildfire and during each of four summer after the fire.  We measured anion (ammonium, nitrate, total dissolved nitrogen, dissolved organic nitrogen, particulate organic nitrogen, total dissolved phosphorus, chloride, and sulfate) and cation (magnesium, potassium, sodium and calcium) concentrations, and discharge at the outlet of the watersheds.  Concentrations of cations (1.5x), ammonium (3x), sulfate (4x), total dissolved phosphorus (6x), total dissolved nitrogen (8x), particulate organic nitrogen (6x), chloride (13x), and nitrate (190x) increased after wildfire.  Export (mg ha-1 day-1) of ammonium (1.4x), cations (2.3x), sulfate (5x), total dissolved phosphorus (10x), total dissolved nitrogen (13x), particulate organic nitrogen (13x), chloride (23x), and nitrate (330x) increased after wildfire.  However, concentration and export of DON was similar before and after wildfire.  Coniferous forests can leak large fluxes of ions after wildfire.


Web Page: wildfire, nutrients, watershed

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