One hundred and four caddisfly species within 42 genera and 17 families were collected from 93 stream sites in the xeric landscape of the lower Colorado River Basin, USA. Species richness showed a significant negative correlation with channel embeddedness. Forestland had higher species richness than grassland, desert, or urban caddisfly assemblages, and fewer caddisfly species occurred in the salt-cedar (Tamarix) than in willow-alder (Salix-Alnus) and cottonwood-sycamore (Populus-Plantanus) riparian communities. Hydroptilidae comprised nearly 35% of the average relative abundance of caddisflies and were generally tolerant of impaired stream environments. Hydroptila arctia composed the greatest relative proportion of species. Adjusted specific conductance and channel embeddedness metrics showed close agreement with published tolerance values for caddisfly species listed by the U.S. Environmental Protection Agency; genera were in less agreement. Amphicosmoecus canax, Brachycentrus americanus, Culoptila moselyi, Glossosoma ventrale, Ochrotrichia ildria, Psychoglypha schuhi, and Ylodes reuteri were most commonly associated with streams with low salinities and low embeddedness, whereas Cheumatopsyche enonis, Hydropsyche auricolor, Hydroptila ajax, Hydroptila arctia, Neotrichia okopa, Smicridea signata, and Smicridea fasciatella reached highest numeric importance in streams with high salinities and embeddedness.
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Vol. 51 • No. 3