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Steps in Developing a Bioassessment and Biocriteria Program
Biocriteria Links
Biological Criteria Development - Establish Thresholds
Biological criteria are formulated in part from the metrics and index values developed from the population of reference sites for a given ecosystem class and are adjusted for aquatic life uses. Other elements of biological criteria are historical information, the consensus opinion of objective regional experts, and in some instances, empirical model results. Each class requires a separate reference characterization (hence, separate reference sites) and separate biocriteria.
Biological criteria are statements (narrative) or values (numeric) that describe the biological integrity of aquatic communities inhabiting waters of a given designated aquatic life use.
The reference condition element of biocriteria may be based on a single aggregated index or established for several biological metrics. For example, a biocriterion for "Class B" sites might be "a index greater than the 50th percentile of least impaired reference conditions." A "Class B" site would be rated impaired if its index fell below the 50th percentile of the "Class B" reference condition.