![[logo] US EPA](https://webarchive.library.unt.edu/eot2008/20081020231455im_/http://www.epa.gov/epafiles/images/logo_epaseal.gif){kind=logo}
Aquatic Life Use Support (ALUS)
Biocriteria Links
Additional Information on Biological Assessment of ALUS for Wadeable Streams and Rivers
The following information may be useful to States in making ALUS determinations based on biological and associated habitat data. Biological assessments are evaluations of the biological condition of waterbodies using biological surveys and other direct measurements of resident biota in surface waters and comparing results to the established biological criteria. They are done by qualified professional staff trained in biological methods and data interpretation. The utility of biological measures has been demonstrated in assessing impairment of receiving waterbodies, particularly that caused by nonpoint sources and nontraditional water quality problems such as habitat degradation. Biological assessments are key to determining whether functional, sustainable communities are present and whether any of these communities have been modified beyond the natural range of the reference condition. Functional and sustainable implies that communities at each trophic level have species composition, population density, tolerance to stressors, and healthy individuals within the range of the reference condition and that the entire aquatic system is capable of maintaining its levels of diversity and natural processes in the future.
The techniques for biosurveys are still evolving, but there have been significant improvements in the last decade. Appropriate methods have been established by EPA, state agencies, and other investigators assessing the condition of the biota. Guidance for development of biocriteria-based programs is provided in the Biological Criteria: National Program Guidance for Surface Waters, and Biological Criteria: Technical Guidance for Streams and Small Rivers. As biosurvey techniques continue to improve, several technical considerations apply:
- The identification of the reference condition is basic to any assessment of impairment or attainment of aquatic life use and to the establishment of biological criteria.
- A multimetric approach to bioassessment is recommended to strengthen data interpretation and reduce error in judgment based solely on population indices and measures.
- Assessment of habitat structure as an element of the biosurvey is critical to assessment of biological response.
- A standardized index period is important for consistent and effective monitoring.
- Standard operating procedures and an effective quality assurance program are established to support the integrity of the data.
- A determination of performance characteristics of the bioassessment provides an understanding of the data quality for the assessment.
- An identification of the appropriate number of sampling sites that are representative of a waterbody is an important consideration in evaluating biological condition.