Urbanization increases stormwater runoff into streams, resulting in channel erosion, and increases in sediment and nutrient delivery to receiving water bodies. Stream restoration is widely used as a Best Management Practice to stabilize banks and reduce sediment and nutrient loads. While most instream nutrient retention measurements are often limited to low flow conditions, most of the nutrient load is mobilized at high stream flows in urban settings. We, therefore, use a process-based stream ecosystem model in conjunction with measurements at low flows and focus on estimation of stream nitrogen retention over the full streamflow distribution. The model provides a theoretical framework to evaluate the geomorphic, hydrologic, and ecological factors that are manipulated by stream restoration, and drive nitrogen retention. We set a model for a pool-riffle sequence restored stream (190 m) in Baltimore County, Maryland and calibrated the model to the in situ measured primary production (Nash–Sutcliffe model efficiency coefficient [NSE] NSE = 0.89), respiration (NSE = 0.74), and nitrate uptake lengths (R² = 0.88). At the daily scale, simulations showed low nitrogen retention during high flows due to high transport rates, mobilization of stored hyporheic nitrogen, and scouring of periphyton biomass. This result underscores the need to reduce contributing watershed runoff flashiness to promote aquatic nutrient cycling and retention. At monthly and yearly time scale, model predicted a higher percent reduction in summer than in winter and estimated 5.7%–9.5% of annual nitrate reductions. While the model was tested in a pool-riffle sequence restoration design, the approach can be adapted to evaluate a range of channel restoration design characteristics, and the effects of upland watershed restoration to mitigate stormwater loading through both restored and unrestored streams.

中文翻译：

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使用数据模型方法评估河道恢复在减少城市集水区氮排放方面的有效性

城市化增加了流入河流的雨水径流，导致河道侵蚀，并增加了向接收水体输送的沉积物和养分。河流恢复被广泛用作最佳管理实践，以稳定河岸并减少沉积物和养分负荷。虽然大多数河内养分保留测量通常仅限于低流量条件，但大部分养分负荷在城市环境中的高流量条件下被动员。因此，我们将基于过程的河流生态系统模型与低流量测量结合使用，并专注于估计整个河流分布中的河流氮保留。该模型提供了一个理论框架来评估由河流恢复操纵的地貌、水文和生态因素，并驱动氮保留。原位测量初级生产（Nash-Sutcliffe 模型效率系数 [NSE] NSE = 0.89）、呼吸作用 (NSE = 0.74) 和硝酸盐吸收长度 ( R ² = 0.88）。在日常规模上，模拟显示由于高传输速率、储存的低流态氮的移动和附着生物生物量的冲刷，在高流量期间氮保留率低。这一结果强调需要减少造成流域径流的闪蒸，以促进水生养分循环和保留。在每月和每年的时间尺度上，模型预测夏季的减少百分比高于冬季，估计每年减少 5.7%–9.5% 的硝酸盐。虽然该模型在水池-浅滩序列修复设计中进行了测试，但该方法可适用于评估一系列渠道修复设计特征，以及高地流域修复对减轻通过修复和未修复河流产生的雨水负荷的影响。