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.
Bibliographical noteFunding Information:
This research was funded by the US Environmental Protection Agency’s (US EPA) Environmental Monitoring and Assessment Program. Preparation of this manuscript was a joint effort of the US EPA’s National Health and Environmental Effects Laboratories in Duluth, Minnesota and Corvallis, Oregon; its cooperators (Oregon State University, CR824682) and contractors. The authors thank M. Arbogast, L. Fore, R. Hughes, Y. Pan, D. Peck, J. Stevenson and J. Stoddard for their considerable efforts checking the quality of the diatom dataset. The authors also appreciate comments on an earlier draft of this manuscript by J. Kingston and J. Thompson. This manuscript has been subjected to the Agency’s peer and administrative review and approved for publication. Approval does not signify that the contents reflect the views of the Agency.
- Eastern United States