02563nas a2200253   4500008004100000245017400041210006900215300001200284490000800296520173200304653002002036653002302056653001002079653001802089100001902107700001802126700001602144700001502160700001702175700001902192700001702211700001502228856006602243       2015                        eng d00aQuantifying ambient nitrogen uptake and functional relationships of uptake versus concentration in streams: a comparison of stable isotope, pulse, and plateau approaches0 aQuantifying ambient nitrogen uptake and functional relationships  a65 - 790 v1253 a<p>Nutrient releases and spiraling metrics are frequently used to quantify the downstream transport of nutrients and to better understand the effects of anthropogenic inputs to downstream waters. Ambient uptake rates in streams can be measured through stable isotope enrichments, while pulse and plateau additions can estimate such rates via extrapolation and modeling techniques, respectively. Data from these releases can be used to estimate ambient uptake rates from nutrient additions and possibly determine the functional relationships between nutrient concentrations and uptake rates. Here, we compared estimated ambient rates calculated from established pulse and plateau approaches, results obtained from new modeling approaches, and rates at ambient concentrations from stable isotope enrichments. Comparative releases of NH4Cl and 15NH4Cl were conducted in four experimental reaches across the grassland Kings Creek and urban Campus Creek, KS. Nutrient uptake was predominantly linear with increasing ammonium. Estimated ambient uptake rates varied among sites, release methods, and data analysis approaches. However, plateau ambient rates from new modeling approaches matched closely with measured ambient rates from isotope enrichments at three sites, suggesting that modeled plateau data may be best for a first look at determining nutrient uptake rates at an individual site. Limitations and benefits of each approach vary; however, baseflow discharge may be a key driver when choosing a method. If possible, multiple methods should be attempted at each location and under each novel set of conditions to determine the best approach prior to designing and implementing a more extensive series of measurements.</p>10aAmmonium uptake10anutrient spiraling10aTASCC10auptake length1 aTrentman, M.T.1 aDodds, W., K.1 aFencl, J.S.1 aGerber, K.1 aGuarneri, J.1 aHitchman, S.M.1 aPeterson, Z.1 aRüegg, J.  uhttps://link.springer.com/article/10.1007%2Fs10533-015-0112-5