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Presented at the NABS Annual meeting, Pittsburgh, Pennsylvania, 2002
in Biogeochemistry
NITROGEN RETENTION IN STREAMS SPANNING A GRADIENT OF AMBIENT STREAMWATER NITROGEN CONCENTRATION.
S.R. Earl1, H.M. Valett1, and C.G. Peterson2. 1Department of Biology, Virginia Tech, Blacksburg, Virginia, USA 24061, 2Department of Natural Science, Loyola University Chicago, Chicago, Illinois, USA 60626
We conducted multiple, short-term injections during which streamwater dissolved inorganic nitrogen (DIN) concentration was incrementally elevated. We hypothesized that streams would exhibit a characteristic saturation response type (SRT) in relation to the stream’s proximity to nitrogen (N) saturation, and that indices of whole-stream N retention (i.e., uptake length SW, uptake rate U, uptake velocity vf) would reflect ambient streamwater N availability. Degree of saturation was estimated by the response to multiple injections (N enrichment concentration versus U), where a positive, linear slope indicates a stream that is not saturated, a Michaelis-Menten type response indicates a stream approaching saturation, and a slope not different from 0 indicates a stream saturated with respect to N. Injections were conducted in streams where ambient, background DIN concentrations ranged from 0.11 to >1.0 mg DIN L-1. SW and U typically increased with increasing N availability across streams, where SW ranged from 1365 to 3363 m and U ranged from 0.09 to 0.15 mg m-2 sec-1, while vf decreased (259 to 59 cm h-1). Our initial survey indicates that these streams exhibited a Michaelis-Menten type response to incremental N enrichment injections. Incorporating streams with a broader range of N availability will help elucidate SRTs.
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