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Biological Response Signatures

Biological indicators are both accurate and sensitive measures of the health of waterways and they can also be used to diagnose sources and causes of pollution. Definite patterns exist in the responses of biological communities to stress (pollution), and finding these patterns can show what types of pollution are present, and sometimes the source of those problems. When the response patterns of the various metrics and components of IBIs (Indices of Biotic Integrity) are identified, these unique combinations of biological community characteristics that aid in distinguishing one impact type over another are referred to as "Biological Response Signatures."

Metrics

When conducting biological assessments, measurements are taken in the field or lab. Metrics (or biological attributes) for each assemblage sample (e.g., benthic invertebrates, fish, periphyton, macrophytes) are calculated from these measurements. The following table presents an example of representative metrics for each type of assemblage.

Biological Assemblage Metric Response to Stress
Benthic Macroinvertebrates No. of taxa Reduced
ETO taxa (ephemeroptera, trichoptera, odonates) Reduced under enrichment, DO, stress
% intolerant species Reduced
% contribution of dominant taxon Increased
% non-insects Reduced
% suspension feeders Reduced
Fish No. of taxa Reduced
% piscivores Reduced
% omnivores Increased
No. of intolerant species Reduced
% tolerant individuals Increased
% planktivores Increased
No. of sunfish species Reduced
Macrophytes No. of taxa Reduced
% exotics or weedy species Increased
% dominant species (by weight) Increased
No. of exotic species Increased
Periphyton Percent Diatom Community Similarity (PSc) Decreased
Species richness Reduced
Pollution Tolerance Index for Diatoms Reduced
% Achnanthes minutissima Increased
Shannon Diversity (for diatoms) Increased

Each metric is then assigned a score which is related to its deviation from the reference (or expected) site values. In more complicated studies, multimetric indices can be calculated, which is the sum of all the metric scores within each biological assemblage.

For more information on biological response signatures:

Please see the discussions on the diagnostic value of biological indicators in EPA's Stressor Identification Evaluation Manual and Ohio EPA's discussion on Biological Response Signatures (24pp, 1.6 MB, About PDF).

To learn more about metrics please visit the following sites:

Biological Indicators | Aquatic Biodiversity | Statistical Primer

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