01856nas a2200181   4500008004100000245009500041210006900136300001300205490000700218520128100225653002001506653001601526653001801542653001901560100001801579700001801597856005901615       2010                        eng d00aSaturation of NO3- uptake in prairie streams as a function of acute and chronic N exposure0 aSaturation of NO3 uptake in prairie streams as a function of acu  a627 -6350 v293 a<p>We conducted a series of stepwise NO3&minus; additions to investigate the response of NO3&minus; uptake to short-term (acute) changes in N concentration in 3 prairie streams. Observed NO3&minus; uptake rates increased with short-term elevations in NO3&minus; concentration and were consistent with linear and Michaelis&ndash;Menten kinetics models. We compiled these data with uptake rates from additional published studies to calculate robust estimates of N uptake kinetics for prairie streams. Half-saturation coefficients based on compiled data were 6.7 &micro;g/L for NH4+ and 67 &micro;g/L for NO3&minus;-N. This difference in half-saturation coefficients suggests that NH4+ is more efficiently assimilated than NO3&minus;, indicating a preference for NH4+ as an N source. Similarly, ambient concentrations of NH4+ and NO3&minus; were less than their respective half-saturation coefficients, and aerial uptake rates were generally &lt;5% of the maximum, suggesting severe limitation of N uptake at ambient conditions. The observed pattern of uptake kinetics suggests that physiological constraints limit biotic N uptake in these low-N streams and contrasts with the pattern of uptake observed in streams with chronically elevated ambient NO3&minus; concentrations.</p>10aBiogeochemistry10aKings Creek10aKonza Prairie10anitrate uptake1 aO'Brien, J.M.1 aDodds, W., K.  uhttps://www.journals.uchicago.edu/doi/10.1899/09-021.1