@article {KNZ00806,
	title = {N uptake as a function of concentration in streams},
	journal = {Journal of the North American Benthological Society},
	volume = {21},
	year = {2002},
	pages = {206 -220},
	abstract = {Detailed studies of stream N uptake were conducted in a prairie reach and gallery forest reach of Kings Creek on the Konza Prairie Biological Station. Nutrient uptake rates were measured with multiple short-term enrichments of NO3- and NH4+ at constant addition rates in the spring and summer of 1998. NH4+ uptake was also measured with 15N-NH4+ tracer additions and short-term unlabeled NH4+ additions at 12 stream sites across North America. Concurrent addition of a conservative tracer was used to account for dilution in all experiments. NH4+ uptake rate per unit area (Ut) was positively correlated to nutrient concentration across all sites (r2 = 0.41, log{\textendash}log relationship). Relationships between concentration and Ut were used to determine whether the uptake was nonlinear (i.e., kinetic uptake primarily limited by the biotic capacity of microorganisms to accumulate nutrients) or linear (e.g., limited by mass transport into stream biofilms). In all systems, Ut was lower at ambient concentrations than at elevated concentrations. Extrapolation from uptake measured from a series of increasing enrichments could be used to estimate ambient Ut. Linear extrapolation of Ut assuming the relationship passes through the origin and rates measured at 1 elevated nutrient concentration underestimated ambient Ut by \~{}3-fold. Uptake rates were saturated under some but not all conditions of enrichment; in some cases there was no saturation up to 50 μmol/L. The absolute concentration at which Ut was saturated in Kings Creek varied among reaches and nutrients. Uptake rates of NH4+ at ambient concentrations in all streams were higher than would be expected, assuming Ut does not saturate with increasing concentrations. At ambient nutrient concentrations in unpolluted streams, Ut is probably limited to some degree by the kinetic uptake capacity of stream biota. Mass transfer velocity from the water column is generally greater than would be expected given typical diffusion rates, underscoring the importance of advective transport. Given the short-term spikes in nutrient concentrations that can occur in streams (e.g., in response to storm events), Ut may not saturate, even at high concentrations.},
	keywords = {LTER-KNZ, advective transport, ammonium, areal uptake, benthos, kinetics, mass transport, Nitrate, nitrogen},
	doi = {10.2307/1468410},
	author = {W. K. Dodds and L{\'o}pez, A.J. and W.B. Bowden and Gregory, S. and Grimm, N.B. and Hamilton, S.K. and Hershey, A.E. and Marti, E. and W.B. McDowell and Meyer, J.L. and Morrall, D. and Mulholland, P.J. and Peterson, B.J. and Tank, J.L. and van der Hoek, D.C.J. and Webster, J.R. and Wollheim, W.}
}
@article {KNZ00783,
	title = {Control of nitrogen export from watersheds by headwater streams},
	journal = {Science},
	volume = {292},
	year = {2001},
	pages = {86 -90},
	abstract = {A comparative 15N-tracer study of nitrogen dynamics in headwater streams from biomes throughout North America demonstrates that streams exert control over nutrient exports to rivers, lakes, and estuaries. The most rapid uptake and transformation of inorganic nitrogen occurred in the smallest streams. Ammonium entering these streams was removed from the water within a few tens to hundreds of meters. Nitrate was also removed from stream water but traveled a distance 5 to 10 times as long, on average, as ammonium. Despite low ammonium concentration in stream water, nitrification rates were high, indicating that small streams are potentially important sources of atmospheric nitrous oxide. During seasons of high biological activity, the reaches of headwater streams typically export downstream less than half of the input of dissolved inorganic nitrogen from their watersheds.},
	keywords = {LTER-KNZ},
	doi = {10.1126/science.1056874},
	author = {Peterson, B.J. and Wollheim, W.M. and Mulholland, P.J. and Webster, J.R. and Meyer, J.L. and Tank, J.L. and Marti, E. and W.B. Bowden and Valett, H.M. and Hershey, A.E. and W.H. McDowell and W. K. Dodds and Hamilton, S.K. and Gregory, S. and Morrall, D.D.}
}
