Abstract Stream channels in the American Southwest are misunderstood because they have been understudied and overgeneralized. This misunderstanding has serious consequences for environmental policy, particularly in defining the scope of jurisdiction under the Clean Water Act. While the current status of regulations defining the scope of jurisdictional waters is in flux, the currently-codified regulations require that jurisdictional tributaries must have a physical, chemical, or biological connection to downstream traditional navigable waters. The lack of consistent flow in arid stream channels causes misinterpretations of physio-chemical indicators that are commonly used in perennial streams of humid environments. Here we overview the use of riparian vegetation as a biological indicator of stream channel presence and connectivity in arid environments. Based on a thorough literature review and synthesis of arid region studies, we found key spatiotemporal patterns of arid riparian vegetation that could potentially be used to determine hydrologic connectivity. Much of the vegetation along arid stream channels is well-adapted to water scarcity and varies in response to differences in geomorphology, hydrology, and land use across multiple scales. Riparian vegetation in arid environments ranges from hydroriparian to xeroriparian and can include, or be made up exclusively, of upland species. Regardless of species type, plants near stream channels tend to be denser and larger than upland plants. Access to reliable water results in denser, larger plants and more water-dependent species. To demonstrate the potential of riparian vegetation as an indicator of connectivity, we conclude with a case study of Little Sycamore Wash in northern Arizona. We used the Normalized Difference Vegetation Index to (1) distinguish between riparian and upland vegetation, and (2) assess connectivity of patches of riparian vegetation. By understanding the spatiotemporal variability of riparian vegetation along arid stream channels, we can make better decisions on their regulation and management.

中文翻译：

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河岸植被作为干旱环境中河流通道存在和连通性的指标

摘要 美国西南部的溪流通道被误解，因为它们没有得到充分的研究和过度概括。这种误解对环境政策造成严重后果，特别是在根据《清洁水法》界定管辖范围方面。虽然目前界定管辖水域范围的法规状态不断变化，但目前编纂的法规要求管辖支流必须与下游传统通航水域有物理、化学或生物联系。干旱河流通道中缺乏一致的流动会导致对常用于潮湿环境的常年河流中的物理化学指标的误解。在这里，我们概述了河岸植被作为干旱环境中河流通道存在和连通性的生物指标的使用。基于对干旱地区研究的彻底文献回顾和综合，我们发现了干旱河岸植被的关键时空模式，这些模式可能用于确定水文连通性。干旱河道沿岸的大部分植被很好地适应了缺水，并随着地貌、水文和土地利用的不同尺度而变化。干旱环境中的河岸植被范围从水生植物到旱生植物，可以包括或完全由高地物种组成。无论物种类型如何，靠近河道的植物往往比陆地植物更密集、更大。获得可靠的水会导致更密集、更大的植物和更依赖水的物种。为了证明河岸植被作为连通性指标的潜力，我们以亚利桑那州北部的 Little Sycamore Wash 为例进行了总结。我们使用归一化差异植被指数 (1) 区分河岸和高地植被，以及 (2) 评估河岸植被斑块的连通性。通过了解干旱河道沿岸植被的时空变异性，我们可以更好地对其进行调控和管理。(2) 评估河岸植被斑块的连通性。通过了解干旱河道沿岸植被的时空变异性，我们可以更好地对其进行调控和管理。(2) 评估河岸植被斑块的连通性。通过了解干旱河道沿岸植被的时空变异性，我们可以更好地对其进行调控和管理。