Treated wastewater, also known as effluent, is discharged into streambeds where it can augment or create aquatic habitat in arid regions. However, discharge fluctuations can result in daily stream drying and rewetting. In this study, we documented flow intermittence and resulting fish stranding and mortality over a 12-week period on an effluent-dependent reach of the lower Santa Cruz River in Tucson, Arizona, USA. We hypothesized that fish stranding would be positively related to the duration of flow prior to drying (increased recolonization potential) and flow recession rates (increased stranding likelihood). Using trail cameras, we monitored drying duration and extent along a 2.1-km reach of river known to experience flow intermittence and counted stranded fish once a week. Drying extent varied widely (range: 0–1.88 km) and averaged 0.79 km ± 0.14 SE. We observed a total of 323 fish strandings across the 12 weeks (range: 0–74 individuals per day; mean: 26.9 ± 8.3 SE). Ninety-nine percent of observed fish were Poeciliidae (63% of which were fry), including non-native western mosquitofish (Gambusia affinis). The recession rate was a positive predictor for the daily stranding count of poeciliids (p = .008). Flow duration was not significant (p = .100) but was included in the top model (R² = 0.782). As urban development continues, the discharge of effluent into rivers and streams will become more common throughout the world. Continued research is needed to understand the benefits and challenges presented by these effluent-driven flow regimes, including their impacts on aquatic taxa.

中文翻译：

---

依赖污水的河流中的每日流量间歇性：流量持续时间和衰退率对鱼类搁浅的影响

处理过的废水，也称为污水，被排放到河床中，在那里它可以增加或创造干旱地区的水生栖息地。然而，流量波动会导致每天的河流干燥和再润湿。在这项研究中，我们记录了美国亚利桑那州图森市圣克鲁斯河下游依赖污水的河段 12 周内的水流间歇性以及由此导致的鱼类搁浅和死亡率。我们假设鱼搁浅与干燥前的水流持续时间（重新定植潜力增加）和水流衰退率（搁浅可能性增加）呈正相关。我们使用跟踪摄像头监测了一条 2.1 公里长的河流的干燥持续时间和范围，该河段已知会经历水流间歇性并每周计算一次搁浅的鱼。干燥程度变化很大（范围：0-1.88 公里），平均为 0.79 公里 ± 0。14 东南。我们在 12 周内共观察到 323 条鱼搁浅（范围：每天 0-74 条；平均值：26.9 ± 8.3 SE）。99% 的观察到的鱼是 Poeciliidae（其中 63% 是鱼苗），包括非本地的西方蚊鱼（Gambusia affinis )。衰退率是 poeciliids 每日搁浅计数的正预测因子 ( p  = .008 )。流动持续时间不显着 ( p  = .100)，但包含在顶级模型中 (R ²  = 0.782)。随着城市发展的继续，污水排放到河流和溪流中将在世界范围内变得更加普遍。需要继续研究以了解这些由污水驱动的流态带来的好处和挑战，包括它们对水生分类群的影响。