Quantifying ambient nitrogen uptake and functional relationships of uptake versus concentration in streams: a comparison of stable isotope, pulse, and plateau approaches
Quantifying ambient nitrogen uptake and functional relationships of uptake versus concentration in streams: a comparison of stable isotope, pulse, and plateau approaches
复制标题
量化环境氮吸收量以及吸收量与溪流中浓度的函数关系：稳定同位素、脉冲和平台方法的比较
作者：
Matt T. Trentman;W. Dodds;Jane S. Fencl;Kayla M. Gerber;J. Guarneri;Sean M Hitchman;Zachary J. Peterson;Janine Rüegg
养分释放和螺旋形指标经常用于量化养分的下游运输，并更好地了解人为输入对下游水域的影响。可以通过稳定同位素富集来测量河流中的环境吸收率，而脉冲和高原添加可以分别通过外推和建模技术来估计这种吸收率。来自这些释放的数据可用于估计营养添加的环境吸收率，并可能确定营养浓度与吸收率之间的功能关系。在这里，我们比较了根据已建立的脉冲和平台方法计算的估计环境速率，通过新的建模方法获得的结果，以及稳定同位素富集在环境浓度下的速率。在草地Kings Creek和城市Campus Creek的四个实验河段进行了NH4Cl和15NH4Cl的对比释放。养分吸收主要与铵的增加呈线性关系。估计的环境吸收率因地点、释放方法和数据分析方法而异。然而，从新的建模方法得到的高原环境速率与从三个地点的同位素富集得到的测量环境速率密切匹配，这表明建模的高原数据可能是确定单个地点营养吸收速率的最佳方法。每种方法的局限性和益处各不相同；然而，在选择方法时，基流排放可能是一个关键驱动因素。如果可能，在设计和实施更广泛的一系列测量之前，应在每个位置和每种新条件下尝试多种方法，以确定最佳方法。
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.