The distance that a nutrient travels as a solute before its removal from the stream water column is known as the uptake length (S_W), which is a functional indicator of environmental quality and integrity. Among nutrient enrichment methods, instantaneous nutrient addition (e.g., slug or pulse) have been proposed as an alternative to plateau and labeled nutrient approaches. Two approaches have been commonly used to estimate S_W and its associated metrics (i.e., areal uptake rate, U; and uptake velocity, V_f) from pulse additions: the spiraling approach, based on the longitudinal variation in nutrient concentrations, and the transport modeling approach, based on the advective and dispersive transport of solutes. However, little is known in how the choice of such analytical methods impacts the estimation of stream uptake parameters and the conclusions we draw from them. Here, we estimated the S_W and V_f of ammonium-nitrogen (NH₄-N) and soluble reactive phosphorus (SRP) from 16 pulsed additions conducted in four low-order streams in southeastern Brazil. We compared metrics estimated by the Tracer Additions for Spiraling Curve Characterization (TASCC) and the One-Dimensional Transport with Inflow and Storage (OTIS) methods, based on the spiraling- and transport-based approaches, respectively. The TASCC:OTIS S_W ratio averaged 0.71 for NH₄-N and 1.01 for SRP, whereas the mean of TASCC:OTIS V_f ratio was 2.04 for NH₄-N and 1.03 for SRP. The results showed that both S_W and V_f estimates differed significantly between methods for NH₄-N, but no statistical differences were observed in SRP estimates. In our study, we highlighted the significant effects of transient storage and variable nutrient concentration on pulsed enrichments. Such information should be considered when choosing which method is appropriate to use for a particular site. Differences between modeling approaches must be addressed when comparing methods to expand our knowledge on broad temporal and spatial patterns of in-stream nutrient uptake.

中文翻译：

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比较基于螺旋和运输的方法来估计来自脉冲添加的河内养分吸收长度

该营养行进作为从流水柱其移除之前的溶质被称为吸收长度（距离小号_{w ^}），这是环境质量和完整性的功能指示器。在营养丰富的方法中，瞬时营养添加（例如，slug 或脉冲）已被提议作为高原和标记营养方法的替代方法。两种方法已被广泛用于估计小号_W¯¯及其相关联的度量（即，分布区吸收速率，ù ;和摄取速度，V _˚F) 来自脉冲添加：螺旋方法，基于养分浓度的纵向变化，以及传输建模方法，基于溶质的平流和分散传输。然而，对于此类分析方法的选择如何影响流吸收参数的估计以及我们从中得出的结论知之甚少。在这里，我们估计小号_W¯¯和V _˚F铵氮（NH ₄-N) 和可溶性活性磷 (SRP) 来自在巴西东南部的四个低阶河流中进行的 16 次脉冲添加。我们分别基于螺旋曲线和基于传输的方法，比较了由 Tracer Additions for Spiring Curve Characterization (TASCC) 和具有流入和存储的一维传输 (OTIS) 方法估计的指标。所述TASCC：OTIS小号_W¯¯比例平均为0.71 NH ₄ -N和1.01 SRP，而TASCC的平均值：OTIS V _˚F比为2.04 NH ₄ -N和1.03 SRP。结果表明，二者小号_W¯¯和V _˚F估计方法之间显著差异为NH ₄-N，但在 SRP 估计中没有观察到统计差异。在我们的研究中，我们强调了瞬时储存和可变营养浓度对脉冲富集的显着影响。在选择适合特定站点使用的方法时，应考虑此类信息。在比较方法以扩展我们对河内养分吸收的广泛时间和空间模式的知识时，必须解决建模方法之间的差异。