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About Biological Indicators
The Clean Water Act requires the use of biological indicators in a variety of programs and settings (see http://www.epa.gov/bioindicators/html/biol2.html). EPA established a biological criteria program to ensure that credible biological indicators were developed and implemented to meet the biological integrity objective of the Clean Water Act.
What Is Biological Integrity?
Biological integrity is commonly defined as "the ability to support and maintain a balanced, integrated, and adaptive community of organisms having a species composition, diversity and functional organization comparable to those of natural habitats within a region" (Karr, J. R. and D. R. Dudley. 1981. Ecological perspectives on water quality goals. Environmental Management 5: 55-68). Biological integrity is equated with pristine conditions, or those conditions with no or minimal disturbance. The reference condition is commonly associated with biological integrity, and the threshold is some proportion of the reference condition. Learn more about reference conditions by reading Best Practices for Identifying Reference Condition in Mid-Atlantic Streams (PDF) (8pp, 1.5MB, About PDF)
Evaluating the health of a body of water through the use of biological indicators is called biological assessment.
The Development of Bioindicators for Water Quality Assessments
"The use of biological indicators to assess the health of our rivers and streams was prompted by some early work conducted by the Illinois Natural History Survey over a century ago. Learn about the circumstances regarding that first biological survey, and the evolution of more rigorous and objective assessment measures leading to the Indices of Biotic Integrity, by reading "A Historical Perspective on Regulatory Biology (PDF)" (134pp, 1.54 MB, About PDF) and "Biological Assessment and Criteria: Building on the Past (PDF)." (16pp, 1.8 MB, About PDF)
Identifying the Causes of Biological Impairments
CADDIS, otherwise known as the Causal Analysis/Diagnosis Decision Information System, is an online application that uses a step-by-step guide, worksheets and examples to help scientists and engineers find, access, organize, share and use environmental information to evaluate causes of biological effects observed in aquatic systems such as streams, lakes and estuaries. It is based on the Stressor Identification (SI) Guidance Document , which describes a formal and rigorous process to identify stressors causing biological impairments in aquatic ecosystems, and a structure for organizing the scientific evidence supporting the conclusions. CADDIS uses the SI process, but also contains updates, clarifications and additional material developed since the SI Guidance Document was published in 2000.