Figure 2

Miles of habitat-impaired rivers and streams reported by the states to the U.S. Environmental Protection Agency. SOURCE: United States Environmental Protection Agency (1994). NOTE: Twenty-five states reported no miles of aquatic-life use impairment associated with habitat degradation.

Ohio's use of quantitative biological criteria had some additional ramifications that affect the statistics related to the Clean Water Act 305[b]. For example, the proportion of stream miles that failed to attain standards increased from 9 percent in 1986 (based on a mix of chemical water-quality and qualitative biological assessments) to 44 percent in 1988, primarily because quantitative biological criteria were included in the assessment process beginning in 1988 (Ohio Environmental Protection Agency, 1988). The nearly fivefold increase in nonattainment illustrates the significant differences that can exist between states that use different assessment methods, especially whether or not biological assessments are included.

These examples demonstrate that relying on chemical water-quality information alone is apt to result in underestimates of environmental degradation. Underestimates are especially likely when assessing watershed-level effects. This is because the interaction of aquatic and riparian habitats, land use, and nutrient dynamics is particularly difficult to measure and characterize without using robust biological assessment tools and indicators. Ironically, much of the concern expressed about using biological criteria has been over the risk of failing to detect water-quality impairment. This concern seems misplaced in light of the preceding examples.

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