Biological Indices

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Biological Indices:

1. Index of Biological Integrity(IBI)

The index of biological integrity is a measure of fish species diversity and species populations.  The criteria used to establish the index for each of the five ecoregions reflects the biological performance exhibited by natural or least impacted habitats of each region based on specific reference sites. The Darby Watershed is in the Eastern Corn Belt Plains region.  The index is a number that reflects total native species composition, indicator species composition, pollutant intolerant and tolerant species composition, and fish condition.  Combined, the higher the calculation, the healthier the aquatic ecosystem; conversely, the lower the index, the poorer the health of the aquatic ecosystem. The highest score is 60. (Ohio EPA)  For more information, please click here.

2. Invertebrate Community Index(ICI)

The invertebrate community index is based on measurements of the macroinvertebrate communities living in a stream or river. It is particularly useful in evaluating stream health because: (1) there are a wide variety of macroinvertebrate taxa, which are known to be pollutant intolerant; and (2) there are a number of macroinvertebrate taxa, which are known to be pollutant tolerant. Like the IBI, the ICI scale is 0 to 60 with higher scores representing healthier macroinvertebrate communities and therefore more biologically diverse communities. (Ohio EPA) For more information, please click here.

3. Qualitative Habitat Evaluation Index(QHEI)

The QHEI index is intended to provide a quantitative evaluation of the qualitative physical characteristics of a given stream reach. This index is similar to the biological indices, IBI and ICI and is measured at each site where IBI data is obtained (Ohio EPA 1989). For more information, please click here.

4. Modified Index of Well Being(Mod. Iwb)

The modified index of well being(Mod Iwb) is based upon the index of well being, which is acalculation of fish mass and density. The modif ed index of well being factors out 13 pollutant tolerant species of fish from certain calculations. This prevents false high readings on polluted streams which have large populations of pollutant tolerant fish.(Ohio EPA)

Biocriteria for Eastern Corn Belt Plains(ECBP)

Index- Site Type WWH EWH MWH
IBI- Headwaters/Wading 40 50 24
Mod. Iwb- Wading 8.3 9.4 5.8
ICI 36 46 22

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Last updated: April 7, 2009.