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

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 (V f ) 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 V f . Nitrate V f was controlled by GPP, not CR, with GPP explaining 75% of variation in NO − 3 V f . 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.