legitimizes their full use. Biological criteria are employed principally as an ambient monitoring and assessment tool through biological surveys. Biological and water-quality surveys, or biosurveys, are monitoring efforts on a water-body or watershed scale. They may range from a focus on a relatively simple setting with one or two small streams, one or two principal stressors, and a handful of sampling sites, to a much more complex effort that includes entire drainage basins, multiple and overlapping stressors, and dozens of sites. Each year, the Ohio Environmental Protection Agency conducts biosurveys in 10-15 different study areas with a total of 250-300 sampling sites.

The Ohio Environmental Protection Agency employs biological, chemical, and physical monitoring and assessment techniques in biosurveys to meet three major objectives:

  • determine the extent to which the habitat classification-specific biological criteria are met;
  • determine if habitat classification criteria assigned to each water body are appropriate and attainable; and
  • determine if any changes in biological, chemical, or physical indicators have occurred since earlier measurements, particularly before and after the implementation of point-source pollution controls or best-management practices for nonpoint sources.

Identifying the causes of observed impairments requires the interpretation of multiple lines of evidence, including water chemistry data, sediment data, habitat data, effluent data, biomonitoring results, and land-use data (Yoder and Rankin, 1995b). The assignment of principal causes of impairment represents the association of impairments with stressor and exposure indicators. The principal reporting venue for this process is a biological and water-quality report for each watershed or subbasin. These reports include summaries of major findings and recommendations for revisions to water-quality standards, future monitoring needs, or other actions needed to resolve existing impairment. Although the principal focus of a biosurvey is to assess whether conditions meet biological criteria, they also address the status of the site for other uses, such as recreation and water supply. Such reports provide the foundation for aggregated assessments, including the Ohio Water Resource Inventory, the Ohio Nonpoint Source Assessment, and other technical bulletins.

Interpreting Results on the Basis of a Longitudinal Reach or Subbasin

It is often useful to plot results as a function of sampling location with major sources of potential impact and the applicable quantitative biological criteria indicated. Figure 6 shows fish and macroinvertebrate community data for the Scioto River during 1980 and 1991. This type of analysis is critical for demonstrating changes through time. Figure 6 represents the results of bioassessments in a 40-

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