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Aquatic Life Use Support (ALUS)
Biocriteria Links
Additional Information
Reference Condition
Reference conditions are described from an aggregate of data best acquired from multiple sites with similar physical dimensions, represent minimally impaired conditions, and provide an estimate of natural variability in biological condition and habitat quality. For determining reference condition, alternative approaches to selection of reference sites include use of historical data, paleoecological data for lakes, experimental laboratory data for select cases, quantitative models, and best professional judgment.
Reference conditions must be stratified (i.e., put into homogenous waterbody classes) to account for much of the natural physical and climatic variability that affects the geographic distribution of biological communities. The Ecoregion Concept recognizes geographic patterns of similarity among ecosystems, grouped on the basis of environmental variables such as climate, soil type, physiography, and vegetation. Currently, efforts are under way in several parts of the country to refine these ecoregions into a more useful framework to classify waterbodies. Procedures have begun in several ecoregions and subecoregions to identify reference conditions within those particular units. In essence, these studies are developing reference databases to define biological potential and physical habitat expectations within ecoregions. The concept of reference conditions for bioassessment and biocriteria is discussed further below.
In developing community bioassessment protocols, reference conditions against which to compare test sites and to judge impairment are needed. Ideally, reference conditions represent the highest biological conditions found in waterbodies unimpacted by human pollution and disturbance. That is, the regional reference site concept is meant to accommodate natural variations in biological communities due to bedrock, soils, and other natural physicochemical differences. Recognizing that pristine habitats are rare (even remote lakes and streams are subject to atmospheric deposition), resource managers must decide on an acceptable level of disturbance to represent an achievable or existing reference condition. Acceptable reference conditions will differ among geographic regions and States and will depend on the aquatic life use designations incorporated into State water quality standards.
Characterization of reference conditions depends heavily on classification of natural resources. The purpose of a classification is to explain the natural biological condition of a natural resource from the physical characteristics. Waterbodies vary widely in size and ecological characteristics, and a single reference condition that applies to all systems would be misleading. A classification system that organizes waterbodies into groups with similar ecological characteristics is required to develop meaningful reference conditions.
The best approach to classifying and characterizing regional reference conditions is determined by the estimated quality of potential reference sites that are available in the region. If a sufficient number of relatively undisturbed waterbodies exist (e.g., primarily forested watersheds), then it is possible to define watershed conditions that are acceptable for reference sites. If no reference sites exist, then reference conditions can be characterized based on an extrapolation of the biological attributes representative of the aquatic biota expected to be found in the region or through other quantitative models. EPA sees the use of a regional reference condition as an important component and goal of State biological programs. The Agency also recognizes that other approaches, such as upstream/downstream sampling, may be necessary.
The Ohio Environmental Protection Agency has been very active in the development of biocriteria based on reference conditions. Ohio's experiences and methods may be useful to other States in developing their biological monitoring and biocriteria programs. Florida DEP has developed a similar approach for defining reference conditions; Arizona DEQ has oriented its reference condition by elevation; and Maine DEC uses a statistically derived-decision model technique that is based on a knowledge of the ecology and expectations in the response to perturbation of the biological attributes to classify and assess its streams. For further information on the development and implementation of biological criteria and assessments, States should consult Biological Criteria: National Program Guidance for Surface Waters, Rapid Bioassessment Protocols for Use in Wadeable Streams and Rivers: Periphyton, Benthic Macroinvertebrates and Fish, and Biological Criteria: Technical Guidance for Streams and Small Rivers.