ASSESSMENT OF STREAMS OF THE EASTERN UNITED STATES USING A PERIPHYTON INDEX OF BIOTIC INTEGRITY.

B.H. Hill¹, A.T. Herlihy², P.R. Kaufmann³, S.J. DeCelles⁴, and M.A. Vander Borgh⁵. ¹Mid-Continent Ecology Division, US Environmental Protection Agency, Duluth, Minnesota USA 55804, ²Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon, USA 97333, ³Western Ecology Division, US Environmental Protection Agency, Corvallis, Oregon USA 97333, ⁴SoBran, Inc., c/o US Environmental Protection Agency, Cincinnati, Ohio, USA 45268, ⁵North Carolina Department of Environment and Natural Resources, Raleigh, North Carolina, USA 27699

Benthic algae collected from 286 eastern United States streams were analyzed for diatom species richness and dominance, the relative abundance of acidobiontic, eutraphentic, and motile diatoms, standing crops of chlorophyll and biomass, and alkaline phosphatase activity; and used to calculate periphyton indices of biotic integrity (PIBI) for reference, moderately impacted, and disturbed streams. PIBI were significantly higher in reference streams for all classifications. The PIBI and its metrics were correlated with many of the chemistry and habitat variables, and canonical correlation analysis revealed three significant environmental gradients which explained 77% of the variance in the PIBI and its metrics. We used the mean 75^th, 25^th, and 5^th percentile scores from the reference sites to set thresholds for excellent, good, fair, or poor condition. Applying these criteria to the cumulative distribution of total stream length in the region, we found that 6% of the stream length was in excellent condition; 25% in good condition; 42% in fair condition; and 27% in poor condition. The sensitivity of the PIBI and its component metrics to environmental stressors supports the use of this index for monitoring ecological conditions in streams in the eastern United States and diagnosing the causes of their impairment.