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

Benthic invertebrates were quantified at summer baseflow from 30 streams draining largely forested watersheds within 7 river catchments (Coosa, Tallapoosa, Tennessee, Black Warrior, Conecuh, Altamaha, Chattahoochee) of 4 Level III ecoregions (Blue Ridge, Southwestern [SW] Appalachians, Piedmont, Southeastern [SE] Plains) of the southeastern USA. The study 1) compared invertebrate distributions classified by large-scale ecoregions against those of small-scale river catchments, and 2) assessed if taxonomic resolution of invertebrate identification (family vs genus/morphospecies) influenced relative classification strength of ecoregions and catchments. Principal components 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 variables. Using simple community presence/absence measures, richness of Ephemeroptera, Plecoptera, and Trichoptera (EPT richness) followed the pattern Blue Ridge > SW Appalachians = Piedmont = SE Plains. When grouped by catchment total and EPT richness tended to be lower in lowland than in upland regions. However, Bray-Curtis presence/absence similarities coupled with flexible UPGMA (unweighted pair-group method using arithmetic averages) analyses revealed that invertebrate assemblages were distinctive among ecoregions both at the genus/morphospecies and family levels. Differences in overall similarity among ecoregions were highly significant, with upland Blue Ridge and lowland SE Plains streams displaying the lowest interecoregional similarity, and Piedmont and SW Appalachians streams displaying the highest similarity. Faunal similarity within a given ecoregion approximated that observed within individual catchments. Family-level groupings were almost as robust at discriminating catchments and ecoregions as were classifications derived from genus/morphospecies. The ecoregion concept appears to be as useful a classification scheme as that derived from smaller river catchments in the delineation of stream invertebrate distributions in the southeastern USA.