Quantifying Stream Ecosystem Condition: New Approaches to Developing Decision Criteria and Diagnostic Tools

The composition of algae, invertebrates and fish communities, and specific characteristics of fish populations, are widely used as tools for monitoring the condition of aquatic resources. The power of these tools would be much greater if there were defendable decision criteria and interpretation methods that allow one to speculate on the specific cause of impacts. Without defendable decision criteria, assessments of impact can be made only in relative terms, and can be questioned. In addition, determining that a site is impacted is of little value unless we can simultaneously determine the root cause of the impact. We have developed both generic decision criteria for ecosystem descriptors considered worth protection (such as fish communities), and more specific decision criteria for surveys of benthic invertebrates in southern Ontario streams based on the protection of fish communities. We have also developed frameworks that utilize algal, benthic and fish communities, and demonstrated the use of fish population characteristics to diagnose the causes of impacts in urbanizing watersheds. This paper discusses why these developments are important to aquatic environmental effects monitoring (AEEM) programs, and describes the approaches we have taken in the development of criteria and diagnostic frameworks.