CS34 River Dynamics
Date: Wednesday, June 12, 2002
Time: 2:45:00 PM
Location: View Royal
 
TankJL, University of Notre Dame, Notre Dame, IN 46556, USA, tank.1@nd.edu
Hall, R, O, University of Wyoming, Laramie, WY 82071, USA, bhall@uwyo.edu
 
PARTITIONING AUTOTROPHIC AND HETEROTROPHIC NUTRIENT UPTAKE IN HEADWATER STREAMS.
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We measured nutrient uptake and whole-stream metabolism in 7 streams in Grand Teton National Park during summers of 1999-2001. Streams were small (3-300 L/s), with low water-column ammonium (1-9 ug/L), nitrate (2-55 ug/L), and SRP (2-29 ug/L). To partition heterotrophic and autotrophic nutrient uptake, we conducted short-term (1-2 hr) diurnal and nocturnal nutrient additions in 4 high-light, alluvial streams. Nutrient demand was lower at night in all 4 streams and nutrient uptake velocities decreased up to 63, 80, and 88% for ammonium, nitrate, and SRP respectively. During Fall 2000, forests surrounding the other 3 shaded streams burned, opening the stream canopy, and both the demand for nitrate and ammonium subsequently increased during Summer 2001. Although organic matter and epilithon standing stocks showed no clear response to fires, using an open-channel method and SF6 to correct for reaeration, measurements of whole-stream metabolism indicated that GPP was 2-3 times higher than estimates prior to the fires. By linking nutrient uptake and whole-stream metabolism measurements, we show that uptake by primary producers can be a large component of nutrient retention in unshaded streams.