Ohio State University

Index of Biotic Integrity (IBI) Scoring


The scoring of this index is based on the following individual site scoring procedures for each 12 categories explained on the previous page (see Index of Biotic Integrity Components in Ohio). Each of those 12 variables can earn a score based on the comparison of a relatively undisturbed site:

5-closely approximates undisturbed site
3-somewhat approximates the undisturbed site
1-does not approximate the undisturbed site at all.

IBI scores can range from 12-60 depending on the amount of disturbance that has taken place at and around the sampling site. Based on the range of possible scores (12-60), the following categories were used for this study:

Exceptional (50-60)
Very Good (49-42)
Good (41-34)
Fair (33-27)
Poor (26-17)
Very Poor (<17)

These categories were slightly modified from the original OEPA classification. Particularly, a 'Very Good' category was added for better descriptive purposes.

These ratings for biological integrity are relative to the general habitat type of the site measured and the ecoregion the site is located within.

Habitat Type
OEPA delineates the following types of water habitats: limited resource waters, modified warmwater habitat (MWH), warmwater habitat (WWH), and exceptional warmwater habitat (EWH). These habitat classifications are used in assessing state water quality standards. The most commonly referred to sites are those modified, exceptional or regular warmwater habitats.

Modified Warmwater Habitat (MWH) types are characteristic of aquatic communities comprised of a predominance of tolerant species, functional feeding guilds, and moderately reduced diversity.

Warmwater Habitat (WWH) types represent general aquatic community components that are characteristic of the majority of Ohio streams and rivers (i.e., such as warmwater fish species and the associated chemical and biological components).

Exceptional Warmwater Habitat (EWH) types are used to classify rivers and streams with unusual and unique assemblages of aquatic life (i.e., significant populations of endangered and declining species and unusually good chemical qualities).

Ecoregion Importance
The IBI value will vary depending on general landscape characteristics such as geology, topography, climate, etc. With so many variables involved, it is necessary to assess IBI in context of ecoregions. For the Great Miami Watershed, the ecoregion frame of reference is the Eastern Cornbelt Plains Ecoregion. In this ecoregion, the average IBI value is 40 for EWH and WWH types and 24 for MWH. These averages can be used as a comparison unit against particular sites within the region.

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