Modification and Assessment of an Index of Biotic Integrity to Quantify Stream Quality in Southern Ontario

A multivariate measure of stream quality, the Index of Biotic Integrity (IBI), was adapted to southern Ontario and calibrated to watershed land use on a variety of spatial scales. The fish fauna at 209 stream locations on 10 watersheds near Toronto, Ontario, was sampled with a backpack electrofisher in the summers of 1984 and 1985 to provide biological information for the IBI. Watershed urbanization, forest cover, and riparian forest were measured from 1:50,000 scale topographic maps and related to IBI estimates by linear regression. Of the biological measures tested, species richness, local indicator species (brook trout (Salvelinus fontinalis) and Rhinichthys spp.), abundance of large piscivores, fish abundance, and incidence of blackspot disease were found to contribute significantly to IBI estimates. Variation in IBI estimates at the same location ranged from 0 to 8% within the sample season and from 0 to 24% between years. Linear models based on measures of watershed urbanization and forest cover accounted for 11–78% of the variation in IBI scores, depending on the spatial scale of the analysis. Significant IBI/land use relationships were found with whole-basin IBI estimates and for IBI estimates from individual stream reaches. Land use immediately upstream of sample stations was most strongly associated with stream quality as measured by the IBI.