A Biotic Index for the Southeastern United States: Derivation and List of Tolerance Values, with Criteria for Assigning Water-Quality Ratings

North Carolina's Division of Environmental Management has a large number of semiquantitative stream macroinvertebrate collections that have been assigned water-quality ratings. These semiquantitative data use abundance values of Rare = 1 Common = 3, and Abundant = 10, allowing the calculation of mean abundance (range = 0-10) for each taxon across five water-quality classes. This information was used to derive tolerance values and classification criteria for a south-eastern biotic index Classification criteria were adjusted for both season and ecoregion, but no corrections were required for stream size. Tolerance values are listed for >500 North Carolina taxa, and are compared with a similar Wisconsin data base.