Thursday, May 29, 2008 - 9:30 AM
508

Do annual cycles of light availability and snow-melt drive ammonium uptake dynamics in an arctic spring stream?

Alexander D. Huryn1, J. P. Benstead2, Stephanie M. Parker1, and J. B. Ramsey2. (1) Department of Biological Sciences, University of Alabama, Box 870206, Tuscaloosa, AL 35487, (2) Department of Biological Sciences, The University of Alabama, Box 870206, Tuscaloosa, AL 35487

We investigated factors controlling the productivity of an Arctic spring stream.  Ivishak Spring (North Slope, Alaska) shows the stable discharge (~80 L/s) and temperature (~4-7°C) typical for spring streams.  It is unusual, however, in having an annual fluctuation of light incidence from 24 hrs/d (summer) to essentially 0 hrs/d (winter).  Consequently, Ivishak Spring is ideal for testing hypotheses addressing light availability, gross primary production (GPP), community respiration (CR), and nutrient cycling.  GPP and CR, from March to November 2007, were ~540 and 2800 g C/m2—similar to highly productive temperate and tropical stream systems.  Daily GPP ranged from 0.3 gC/m2/d (November) to 4.3 gC/m2/d (July); CR ranged from 2.1 gC/m2/d (November) to 25.0 gC/m2/d (May).  Areal uptake of ammonium-N (=U; 6.7 mg/m2/d, October; 174.4 mg/m2/d, May; ~17 g/m2 March-November), was correlated with ln-GPP (r=+0.60) and ln-CR (r=+0.92).  Month-to-month variation in GPP and CR is attributed to light fluctuation.  We suspect that the annual extreme of CR, however, is due to labile DOC entering the stream during May snowmelt.  Variation in ammonium-N uptake appears to be driven by processes associated with extreme levels of CR during snowmelt (33+% of annual uptake) and by elevated levels of CR and GPP during summer.


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