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What are Biocriteria and Bioassessment Data?

The presence, condition and numbers of types of fish, insects, algae, plants, and other organisms are data that together provide direct, accurate information about the health of specific bodies of water. Studying these factors as a way of evaluating the health of a body of water is called biological assessment.  Biological criteria (biocriteria) on the other hand, are a way of describing the qualities that must be present to support a desired condition in a waterbody, and they serve as the standard against which assessment results are compared.  The terms biological assessment and biological criteria have sometimes been used interchangeably. This confusion is not surprising considering the interrelationship between the two terms:

Biological Criteria
narrative or numeric expressions that describe the reference biological integrity (structure and function) of aquatic communities inhabiting waters of a given designated aquatic life use. Biocriteria are based on the numbers and kinds of organisms present and are regulatory-based biological measurements.
Biological Assessments
are an evaluation of the biological condition of a waterbody using biosurvey data and other direct measurements of resident biota in surface waters.

How are Biocriteria Derived?

Biocriteria are derived from biological assessments involving integrated measures - indices - of the composition, diversity, and functional organization of a reference aquatic community. The reference conditions should be the foundation for biocriteria. It should also represent unimpaired or minimally impaired conditions and the "high end" of the state's designated aquatic life use classification system (e.g., Ohio's "excellent warmwater habitat" or Maine's "Class A, as naturally occurs").

Biocriteria "scores" (Ohio multimetric approach) or "clusters" (Maine statistical approach) can be established for the different biological conditions characterized by a tiered aquatic life use classification. Biological assessments are then conducted to determine if a waterbody is attaining its specified designated aquatic life use by comparing the assessment results with the biocriteria established for that waterbody.

How Do Biocriteria and Chemical Water Quality Criteria Differ?

It is important to keep the differences between biological criteria and chemical water quality criteria clearly in mind when considering application of biocriteria. Many questions about the application of biological criteria assume they are alternatives to chemical water quality criteria. Biological criteria, however, will have a different role in water resource management than chemical whole effluent toxicity (WET) or physical water quality criteria.

Biological assessments provide direct measures of the cumulative response of the biological community to all sources of stress: they measure the condition of the aquatic resource to be protected. Therefore, biocriteria set the biological quality goal, or target, to which water quality can be managed, rather than the maximum allowable level of a pollutant or other water quality condition in a water body.

Physical, chemical, and WET water quality criteria are designed to protect the biological community of a water body from different categories of stress: toxic levels of pollutants and unhealthy physical conditions (high pH, low dissolved oxygen, high turbidity, etc.). Most importantly, physical, chemical, and WET criteria are designed to PREVENT harmful effects on aquatic life BEFORE they occur.

Key Concepts of Bioassessments and Biocriteria

What is biological integrity?  How are ecoregions used?  What is a multimetric index?  There are a number of important key concepts that need to be understood when establishing a biocriteria program.  Find out more information on these key concepts and some of the lessons learned from developing biocriteria across the country.

How are Bioassessment Data and Biocriteria Used?

One of the most meaningful ways to answer basic questions about the quality of the nation's waters is to observe directly the communities of plants and animals that live in them. Because aquatic plants and animals are constantly exposed to the effects of various stressors, these communities reflect not only current conditions, but also stresses and changes in conditions over time and their cumulative impacts. Bioassessment data is invaluable for managing our aquatic resources and ecosystems. We can use it to set protection and restoration goals, to decide what to monitor and how to interpret what is found, to identify stresses to the waterbody and decide how they should be controlled, and to assess and report on the effectiveness of management actions.

To better serve these key management functions, biological assessments and adoption of biological criteria must become an equal component of water quality management programs along with chemical, physical, and toxicity based water quality standards. By themselves, traditional chemical, physical and toxicity assessments cannot fully answer questions about the ecological integrity of a waterbody, or determine whether aquatic resources are being protected. Relying on traditional chemistry alone may lead to situations in which meeting chemical and toxicity standards may not be enough to fully protect the aquatic community, or conversely, to situations in which the community remains in satisfactory condition despite a failure to attain standards. This is illustrated below with the six leading causes of aquatic life use impairment from Ohio rivers and streams. Stressors such as poor habitat quality, altered stream flows,high turbidity and sedimentation, low dissolved oxygen concentrations, eutrophication, and contaminated sediments are proving more important than typically regulated pollutants in limiting the attainment of designated aquatic life uses.

Six Leading Causes of Aquatic Life Use Impairment

This and other examples reinforce the need for a more comprehensive suite of measures and indicators to characterize the ecological health of a waterbody. The presence, condition and numbers of types of fish, invertebrates, amphibians, algae, and plants are data that together provide direct, accurate information about the health of specific bodies of water. With rigorous, robust data, moreover, bioassessment data can also help distinguish among potential stressors, such as those leading the causes of Ohio's water quality impairments. Establishing credible relationships between stressors and impairments can help managers and the public identify likely causes of the problems and take the most appropriate actions to correct them. And finally, the bioassessment data serves as a measure to evaluate the effectiveness of management actions as reflected in the responses and improved conditions of biological communities.

Biological Indicators

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