Correspondence between stream macroinvertebrate assemblages and 4 ecoregions of the southeastern USA

Benthic invertebrates were quantified at summer baseflow from 30 streams dr aining largely forested watersheds within 7 river catchments (Coosa, Tallap oosa, Tennessee, Black Warrior, Conecuh, Altamaha, Chattahoochee) of 4 Leve l III ecoregions (Blue Ridge, Southwestern [SW] Appalachians, Piedmont, Sou theastern [SE] Plains) of the southeastern USA. The study 1) compared inver tebrate distributions classified by large-scale ecoregions against those of small-scale river catchments, and 2) assessed if taxonomic resolution of i nvertebrate identification (family vs genus/morphospecies) influenced relat ive classification strength of ecoregions and catchments. Principal compone nts analysis indicated that environmental differences across catchments and ecoregions were associated more with variation in baseflow water chemistry leg., total alkalinity, conductivity) than with geomorphic or geographic v ariables. Using simple community presence/absence measures, richness of Eph emeroptera, Plecoptera, and Trichoptera (EPT richness) followed the pattern Blue Ridge > SW Appalachians = Piedmont = SE Plains. When grouped by catch ment total and EPT richness tended to be lower in lowland than in upland re gions. However, Bray-Curtis presence/absence similarities coupled with flex ible UPGMA (unweighted pair-group method using arithmetic averages) analyse s revealed that invertebrate assemblages were distinctive among ecoregions both at the genus/morphospecies and family levels. Differences in overall s imilarity among ecoregions were highly significant, with upland Blue Ridge and lowland SE Plains streams displaying the lowest interecoregional simila rity, and Piedmont and SW Appalachians streams displaying the highest simil arity. Faunal similarity within a given ecoregion approximated that observe d within individual catchments. Family-level groupings were almost as robus t at discriminating catchments and ecoregions as were classifications deriv ed from genus/morphospecies. The ecoregion concept appears to be as useful a classification scheme as that derived from smaller river catchments in th e delineation of stream invertebrate distributions in the southeastern USA.