Ecosystem metabolism controls nitrogen uptake in streams in Grand Teton National Park, Wyoming

Hall, Robert O., Jennifer L. Tank

Limnol. Oceanogr., 48(3), 2003, 1120-1128 | DOI: 10.4319/lo.2003.48.3.1120

ABSTRACT: Streams and rivers regulate nitrogen transport (N) to downstream ecosystems. Rates of N uptake can be high in streams, but controls on the variation in uptake rates of N among streams are not known. We measured ammonium (NH+4) and nitrate (NO-3 ) uptake velocities (Vf) and compared these with whole-reach estimates of gross primary production (GPP) and community respiration (CR) in 11 low-nitrogen streams in Grand Teton National Park, Wyoming. We predicted that increased metabolism would positively relate to higher N demand because of stoichiometric N requirements associated with carbon fixation. Rates of GPP and CR explained 82% of variation in NH+4 Vf. Nitrate Vf was controlled by GPP, not CR, with GPP explaining 75% of variation in NO-3 Vf. Nitrate concentrations did not increase downstream during NH+4 addition in all streams, including streams with zero NO-3 uptake, suggesting low nitrification rates relative to NH+4 uptake. Using a stoichiometric model, we show that areal N uptake estimated from microbial and algal production was similar to measured areal N uptake. High primary production could be a prerequisite for streams exhibiting high NO-3 uptake rates.

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