Impervious surface cover increases peak flows and degrades stream health, contributing to a variety of hydrologic, water quality, and ecological symptoms, collectively known as the urban stream syndrome. Strategies to combat the urban stream syndrome often employ engineering approaches to enhance stream-floodplain reconnection, dissipate erosive forces from urban runoff, and enhance contaminant retention, but it is not always clear how effective such practices are or how to monitor for their effectiveness. In this study, we explore applications of longitudinal stream synoptic (LSS) monitoring (an approach where multiple samples are collected along stream flowpaths across both space and time) to narrow this knowledge gap. Specifically, we investigate (1) whether LSS monitoring can be used to detect changes in water chemistry along longitudinal flowpaths in response to stream-floodplain reconnection and (2) what is the scale over which restoration efforts improve stream quality. We present results for four different classes of water quality constituents (carbon, nutrients, salt ions, and metals) across five watersheds with varying degrees of stream-floodplain reconnection. Our work suggests that LSS monitoring can be used to evaluate stream restoration strategies when implemented at meter to kilometer scales. As streams flow through restoration features, concentrations of nutrients, salts, and metals significantly decline (p < 0.05) or remain unchanged. This same pattern is not evident in unrestored streams, where salt ion concentrations (e.g., Na⁺, Ca²⁺, K⁺) significantly increase with increasing impervious cover. When used in concert with statistical approaches like principal component analysis, we find that LSS monitoring reveals changes in entire chemical mixtures (e.g., salts, metals, and nutrients), not just individual water quality constituents. These chemical mixtures are locally responsive to restoration projects, but can be obscured at the watershed scale and overwhelmed during storm events.

不透水的地表覆盖物增加了峰值流量并降低了河流的健康状况，导致各种水文、水质和生态症状，统称为城市河流综合症。对抗城市河流综合症的策略通常采用工程方法来加强河流与洪泛区的重新连接，消散城市径流的侵蚀力，并增强污染物的滞留，但这些做法的效果如何或如何监测其有效性并不总是清楚的。在这项研究中，我们探索了纵向流天气（LSS）监测（一种沿着空间和时间的流路收集多个样本的方法）的应用，以缩小这一知识差距。具体来说，我们研究了（1）LSS 监测是否可用于检测沿纵向流径的水化学变化，以响应河流-洪泛区重新连接，以及（2）恢复工作改善河流质量的规模有多大。我们展示了五个流域的四种不同类别的水质成分（碳、营养物、盐离子和金属）的结果，这些流域具有不同程度的溪流-洪泛区重新连接。我们的工作表明，LSS 监测可用于评估在米到公里尺度上实施的河流恢复策略。当溪流流经恢复地物时，营养物、盐和金属的浓度显着下降 ( p  < 0.05) 或保持不变。这种相同的模式在未恢复的河流中并不明显，其中盐离子浓度（例如，Na ⁺、Ca ²⁺、K ⁺）随着不渗透覆盖层的增加而显着增加。当与主成分分析等统计方法结合使用时，我们发现 LSS 监测揭示了整个化学混合物（例如盐、金属和营养物）的变化，而不仅仅是单个水质成分的变化。这些化学混合物对当地的恢复项目有反应，但在流域范围内可能会被掩盖，并在风暴事件期间被淹没。