The multiple assemblage and multimetric assessment approach outlined here is designed to address elements and processes associated with community balance, trophic structure, and richness. This guidance is not intended to replace existing biological assessment or biocriteria programs. Although not designed to push the envelope of lake bioassessment, this document was developed to provide methods that are technically credible, practical, and geared toward the genuine needs and resources of natural resource agencies. Investigators and resource managers, however, have long recognized that water column measurements reflect conditions only at the time of sampling. As an important supplement to chemical sampling, biological measurements can reflect both current conditions and temporal changes in waterbodies, including the cumulative effects of successive disturbances.
Biological criteria are benchmarks for water resource protection and management decision making.
Expressed as numeric values or narrative expressions, they measure attainment of biological integrity. In turn, biological integrity describes the most robust aquatic community to be expected in a natural condition in a water resource relatively unaffected by human activities. The development of biocriteria by natural resource agencies depends on the assessment of conditions at reference sites. Reference sites are not necessarily pristine, although they must exhibit only minimal impairment relative to the overall region of study. Based on biological sampling, or surveys, a bioassessment of multiple sites is done, resulting in values that represent the biological potential for waters in the region.