Vegetative and geomorphic complexity at tributary junctions on the Colorado and Dolores Rivers: a blueprint for riparian restoration
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Habitat complexity in rivers is linked to dynamic fluvial conditions acting at various spatial scales. On regulated rivers in the western United States, tributaries are regions of high energy and disturbance, providing important resource inputs for riparian ecosystems.
This study investigated spatial patterns and extents of tributary influence on riparian habitat complexity in the near channel zone along regulated reaches of the Colorado (> 200 km) and Dolores Rivers (~ 300 km) in the western United States. Because tributary confluences are regions of increased dynamism, we hypothesized that: (1) geomorphic and land cover complexity would be greatest close to tributary junctions and decrease with distance from tributaries; and (2) patterns in complexity would vary across different sized spatial units.
Using a combination of remote sensing and spatial analysis, we classified fluvial features and land cover classes to investigate patterns longitudinally at 10-, 25-, and 100-m spatial units in the near channel zone of two regulated rivers.
Using change point analysis and randomization tests, we detected shifts in riparian habitat complexity closer to tributary junctions. Patterns varied across 10-, 25-, and 100-m spatial units in the near channel zone, with significance (p ≤ 0.05) recorded for 10- and 25-m spatial units.
Tributary junctions deliver critical resource inputs on regulated systems, providing for increased geomorphic and land cover diversity upstream and downstream of tributaries. We found that patterns of response were non-linear and discontinuous, varying across spatial units and potentially influenced by the degree of mainstem flow regulation.
KeywordsRiparian Complexity Tributary Channel class Cover class Spatial unit Randomization test Restoration
We thank C. Torgersen for his review and comments on an earlier version of this manuscript. We thank J. Rice and K. Johnson for their input and guidance on this research. Funding was provided by the United States Department of Interior Bureau of Reclamation Water Smart Grant Program through the Southern Rockies Landscape Conservation Cooperative. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
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