Development of a stream habitat index for use with an Index of Biotic Integrity in the St. Croix River Basin, Minnesota

More than 70 streams in the St. Croix River Basin in Minnesota were sampled for fish community composition and physical habitat during 1996–98. A habitat index was developed based on measurements, field observations, and land use. The objective was to develope a habitat index for use to evaluate water quality and the effects of nonpoint-source effects not associated with habitat degradation. Core habitat variables were determined with a concurrence analysis using principal components of two subsets of sites with pristine or least affected habitat. Although core habitat variables differed slightly between data sets, sufficient similarities allowed development of an index. The index (the sum of pluses or minuses dependent on the variable’s correlation to biotic integrity), composed of 12 core habitat variables in 5 classification groups (hydrology, geomorphology, substrate, instream habitat, and riparian/land use), was able to distinguish sites with low Index of Biotic Integrity scores not related to habitat degradation.