Abstract
Stream classifications are important for understanding stream ecosystem diversity while also serving as tools for aquatic conservation and management. With current rates of land and riverscape modification within the United States (US), a comprehensive inventory and evaluation of naturally occurring stream habitats is needed, as this provides a physical template upon which stream biodiversity is organized and maintained. To adequately represent the heterogeneity of stream ecosystems, such a classification needs to be spatially extensive where multiple stream habitat components are represented at the highest resolution possible. Herein, we present a multi-layered empirically-driven stream classification system for the conterminous US, constructed from over 2.6 million stream reaches within the NHDPlus V2 stream network. The classification is based on emergent natural variation in six habitat layers meaningful at the stream-reach resolution: size, gradient, hydrology, temperature, network bifurcation, and valley confinement. To support flexibility of use, we provide multiple alternative approaches to developing classes and report uncertainty in classes assigned to stream reaches. The stream classification and underlying data provide valuable resources for stream conservation and research.
Highlights
Background & SummaryClassification systems reveal the structure and relationships among groups of objects, and in doing so, they help us understand complex systems by drawing inferences about the laws that govern those relationships[1]
We evaluated the degree of upstream regulation by impoundments using the degree of regulation (DOR) (% of annual discharge stored by upstream dams)[44], provided by StreamCat
“Moderately confined” stream reaches had valley bottoms with widths >4X river width but only covered 25–50% of the stream reach length, or if greater than 50% coverage of stream length, Mixture Model Classes Intermittent Flashy 1 Late Timing Runoff Perennial Runoff 1 Perennial Runoff 2 Super Stable Groundwater Stable High Baseflow Intermittent Flashy SW Snowmelt 2 Perennial Flashy Intermittent Flashy 2 Western Coastal Runoff Stable High Runoff Harsh Intermittent Snowmelt 1 Glacial High Runoff
Summary
Classification systems reveal the structure and relationships among groups of objects, and in doing so, they help us understand complex systems by drawing inferences about the laws that govern those relationships[1]. The above principles are a stark contrast to the many previous national-scale stream classification efforts, which have either classified discrete observations (e.g., stream monitoring points)[2], used deductive approaches for grouping streams[10,24], and/or classified singular, as opposed to multiple, habitat components, primarily hydrology[22] While these approaches have enriched our understanding of stream function, they are limited in their ability to comprehensively represent the emergent properties of stream ecosystems and their habitat components across large regions[6,7]. A comparable stream classification of this scope and resolution has not been documented in the literature, but provides a valuable resource for stream management, conservation, and research applications
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