Biological criteria are narrative descriptions or numerical values that describe the reference macroinvertebrate, or aquatic insect, communities inhabiting waters that have been given a designated aquatic life use. The department’s primary intended uses of biological criteria are:
- To establish regional attainment goals that are relevant to aquatic life use and resource protection
- To serve as a scientifically valid benchmark
- To provide a sound, scientific basis for biological assessment of the status of aquatic communities
The department initiated the process of biological criteria development in 1992. Narrative portions of biological criteria were then established in the 1994 revision of the Missouri water quality standards. The department researched and developed a biological criteria framework for the wadeable, perennial streams of Missouri using general guidance from EPA, the Department of Natural Resources, University of Missouri – Columbia, and Missouri Resource Assessment Partnership.
Biological criteria development consisted of:
- Delineating aquatic ecoregions of Missouri
- Designating reference streams
- Surveying the habitat and macroinvertebrate communities
- Selecting and calibrating biological metrics
- Developing a framework for numeric biological criteria
- Establishing numeric criteria for wadeable, perennial streams of Missouri
Missouri was divided into 19 aquatic ecoregions, termed ecological drainage units. Numeric biological criteria for benthic macroinvertebrates were researched from 1992 through 2002. Sixty-two wadeable, perennial reference streams were selected as reference streams. Each is classified as cold water or warm water, and riffle/pool or glide/pool stream types. Ecological drainage units, in combination with stream type and season, provide a framework for which numeric criteria are generated for 50 categories of streams. Criteria were first calculated in 2002. Four primary biological metrics were selected: taxa richness, biotic index, Shannon diversity Index, and Ephemeroptera, Plecoptera, Trichoptera taxa. These four metrics are then translated into a multi-metric index, known as the Macroinvertebrate Stream Condition Index Score, that indicates whether the stream is fully, partially, or not supportive of biological life. Numeric criteria continue to be refined as reference stream data is collected.
Information regarding the criteria development process and initial numeric criteria are documented in the 1997 University of Missouri document: Biological Criteria for Streams of Missouri and the 2002 Department of Natural Resources document: Biological Criteria for Wadeable/ Perennial Streams of Missouri. Procedures specific to sampling streams for macroinvertebrates and assessing the results include: