The following Biotic Indices are calculated from the benthic macro-invertebrate data:
 Hilsenhoff Family Biotic Index (FBI)
Taxa Richness (TR)
Ephemeroptera, Plecoptera, Thrichoptera Taxa Richness Index (EPT)
Bentic Invertebrate Species Sensitivity
Hilsenhoff Family Biotic Index (FBI)
The Hilsenhoff Family Biotic Index (FBI) indicates organic and nutrient pollution and provides an estimate of water quality for each site using established pollution tolerance values for each taxa. The following table shows how water quality is evaluated using the Family Biotic Index.
Taxa Richness (TR)
Taxa Richness (TR) indicates the health of the community through it's diversity, and increases with increasing habitat diversity, suitability, and water quality (Plafkin et al., 1989). TR equates the total number of taxa found within the sample. The healthier the community is, the greater the number of taxa found within the community.
Ephemeroptera, Plecoptera, Trichoptera Taxa Richness Index (EPT)
A calculation of taxa richness, such as EPT taxa richness index, will establish the stability of the community. Ephemeroptera (Mayflies), Plecoptera (Stoneflies), and Trichoptera (Caddisflies) are all species that are considered to be very sensitive to poor water quality conditions, therefore the presence of these organisms are indicators of good water quality sites. The higher the populations of these organisms the more stable the site.
Click here to see a sample
of common benthic invertebrates.
Benthic Invertebrate Species Sensitivity
Specific Taxa indexes include:
% dominant
% Midges
% Diptera
% Insects
% non-Dipteran Insects |
% EPT
% Mayflies
% Leeches
% Blackflies |
Taxa Tolerance Catagories
The chart below categorizes the taxa into various pollution tolerances those being sensitive, somewhat sensitive, and tolerant.
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| Click to view larger graph. |
The Jock River Watershed has a total of 5 watercourses sampled: Flowing Creek, Jock River, Hobbs Drain, Kings Creek, and Nichols Creek, with three replicates taken at each sample location. This graph depicts the tolerance index values for Replicate #1, Fall 2003, Jock River Watershed. This tolerance graph shows various families (i.e. % Mayflies) and groups of families (i.e. % Insects) that assist in determining water quality conditions for a given site.
The accompanying chart titled "Taxa Tolerance Categories" puts various organisms into three categories Sensitive, Somewhat Sensitive, and Tolerant. Some general statements can be made for example in the chart both the Jock River site and the Hobbs Drain site have high % Mayflies and % EPT this points toward good water quality conditions at these sites. Conversly both Nichols Creek and Flowing Creek had higher numbers of %Diptera and % Midges , which may indicate impaired conditions at these sites. The % Dominant Index indicates that the Jock River site and the Hobbs Drain site had higher % dominant values indicating lower species diversity, however those species were primarily within the Sensitive Category, which indicates good water quality conditions. Determining health of a watercourse when using Benthic Invertebrates it is important to also consider physical and chemical parameters at the site.
The following breakdown is how these families rate from a sensitivity perspective for various water quality conditions:
| % Simulidae (Blackfly Larvae) |
The chart categorizes these species as "Tolerant", which means that these organisms can live in any water quality conditions. |
| %Hirudinae (Leeches) |
The chart categorizes these species as "Tolerant", which means that these organisms can live in any water quality conditions. |
| % Ephemeroptera (Mayfly) |
The chart indicates these organisms are sensitive to pollution and are generally only found in good water quality conditions |
| % (EPT) Index- Ephemeroptera, Plecoptera, Trichoptera (Mayfly, Stonefly, Caddisfly) |
This index takes three families that are all in the Sensitive category and totals them as a percentage in the sample to indicate water quality health. They are excellent indicators of good water quality and you would typically would want to see high numbers of all three families. |
| % Diptera Index |
The chart categorizes these species as "Tolerant", which means that these organisms can live in any water quality conditions. |
| % Insects Index - Ephemeroptera, Plecoptera, Trichoptera, Anisoptera, Zygoptera, Hemiptera, Megaloptera, Lepidoptera, Coleoptera, flying Diptera, Tabanidae, Culicidae, Tipulidae, Simulidae |
The chart indicates these organisms into all three groups, Tolerant, Somewhat Sensitive and Sensitive to pollution and are found in poor to good water quality conditions |
| % Midges Index Diptera non flying, Ceratopogonidae, Chironomidae |
The chart categorizes these species as "Tolerant", which means that these organisms can live in any water quality conditions |
| % Non Diptera Insect s- Ephemeroptera, Anisoptera, Zygoptera, Plecoptera, Hemiptera, Megaloptera, Trichoptera, Lepidoptera, Coleoptera |
The chart indicates these organisms into two groups, which include Somewhat Sensitive and Sensitive to pollution and are generally only found in good or fair water quality conditions. |
| % Dominant |
This index shows dominance in the sample. The family with the highest # of organism is divided by the total # of organisms in the sample. This gives you % dominant. If a sample has a very high % dominant value than the diversity of that sample is low, which may indicate that the benthic invertebrate populations are unstable. Also with respect to % dominant, depending on what species makes up that value, it can determine water quality conditions. For example as mentioned above if the % dominant species within a sample is the Mayfly than your water quality conditions may be very good, however conversely if the % dominant species is the Blackfly than you may have impaired water quality conditions. |
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