Biological Integrity

After the sorting and identification is complete, BMIs are assessed using three different metrics that include two richness and one tolerance metric. These metrics are integrated into an overall stream score, which is given an integrity rating. Numbers can be calculated from abundance ratings by assigning a simple numbering system (A = 6; C = 3; R = 1). The calculation procedure for each metric is described below:

  • Total Taxa: This metric is simply the total number of different kinds from the entire sample.
  • EPA Taxa: The total number of different kinds from the Ephemeroptera (mayflies), Plecoptera (stoneflies), and Trichoptera (caddisflies) orders.
  • Biotic Index: Multiply the abundance number by the tolerance rating to determine the tolerance score. Add the entire tolerance score column and the abundance column. Divide the total tolerance by the total abundance.
  • Stream Score: The overall stream score is determined using a point scale system, which combines the metrics into a single number and integrity rating.

Additional Information

  • Benthic Macroinvertebrates

    This resource is designed to provide a better understanding of the wide vareity of aquatic invertebrates found in our rivers, streams and wetlands. In addition to images, general information is included about the distinguishing features of the aquatic stage that aid in identification, and a scale for the organisms feeding group, tolerance, size range and habitat. Larval and adult images are also provided for many families.

  • Point Scale

    Point scale for each metric.

  • Level-One Survey Data Sheet

    Level-One survey data sheet example with stream scoring.

  • Advanced Biological Integrity Metrics

    After the counting, sorting and identifications is complete the benthic macroinvertebrate collections are assessed using six metrics. An overall stream score is determined using reference formulas or point system.

  • Spreadsheets for Calculation

    It is very important to correctly assess the data that you collect in order to interpret the results. To be consistent you must maintain a certain level of precision and accuracy in the field and use standard methods when performing all protocols. This will result in comparable data and enable you to monitor trends over time. To aid in the interpretation of stream survey data, WV Save Our Streams provides a variety of spreadsheets that simplify the metric calculations and evaluations. Most of the resources below are Excel spreadsheets but there are also some on-line tools and appelets.

Sample BMI Assessment Score Sheet
Sample BMI Assessment Score Sheet