Assessment of streams of the eastern United States using a periphyton index of biotic integrity

Benthic algae were collected from 272 eastern United States streams and rivers and 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. These data were used to calculate a periphyton index of biotic integrity (PIBI), and values of the index were compared among reference, moderately impacted, and disturbed streams. The level of disturbance was based on stream chemistry, riparian disturbance, or a combined classification. Analyses of variance showed that PIBI was 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 extracted 84% of the variance in the PIBI and its metrics. We used the mean 75th, 25th, and 5th 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 4.3% of the stream length was in excellent condition; 20.8% in good condition; 56.4% in fair condition; and 18.5% 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 as a tool to aid in diagnosing the causes of their impairment.