The Index of Biological Integrity, or IBI, is a scoring system used to measure strong responses to human disturbance, or pollution, in wetlands. WHEP focuses on two biological communities: plants and macroinvertebrates (small organisms in the water without a backbone: insects, leeches, snails, etc.).
 
The Minnesota Pollution Control Agency selected a variety of metrics (measurements) which focus on those organisms which best reflect wetland quality or health. Each metric is evaluated based on the identified specimens and their abundance. They reflect organism presence and relative abundance. Depending on the result of the metric, each is awarded a score of one, three or five. The scores for each metric are combined to calculate a total score, this is the IBI.  The higher the score, the higher the likelihood of a healthy wetland.
 
The IBI score is then converted to an overall rating to give the wetland a qualitative description (poor, moderate, excellent). A wetland described as poor has a minimal variety of organisms and a large number of them would likely not be sensitive to pollution.  A wetland of excellent quality would have a higher variety of organisms and contain those species that are more sensitive to human disturbance or pollution.  
 
The two IBIs (macroinvertebrates and vegetation) have slightly different ratings based on the scoring range. This is due, in part, to the number of metrics evaluated in each IBI; six for the macroinvertebrate and seven for the vegetation IBI.
 

Review the macroinvertebrate metrics:
The metrics (measures) listed below are used to assess the health of wetlands.  Each metric receives a score of one, three, or five.  The six metrics are then totaled to produce an overall IBI score.  The greater the score, the greater the indication of a healthy wetland.  The score is then interpreted into a general health rating of Excellent, Moderate or Poor.

Metric #1: Number of kinds of leeches

 The number of kinds of leeches found in dipnet and bottletrap samples is greater in healthier wetlands.  There is one kind of leech that tends to increase in relative numbers in more polluted wetlands, but overall, more leech taxa indicates less disturbance.  Leeches feed on a variety of different kinds of prey, both invertebrate and vertebrate.  Very few kinds of leeches suck blood from mammals.

Metric #2: Corixidae proportion metric

Ratio of water boatman to other true bugs and beetles in the bottle trap sample.  All aquatic beetles and most true bugs are predators, mostly feeding on other invertebrates.  Many of the corixid bugs feed on algae and detritus that tends to increase in polluted wetlands.  The corixid bugs tend to increase in proportion to the total count of individuals of beetles and bugs found in the bottletrap samples.  This is the only metric that relies only on data from bottle trap, and the only one that counts the number of individuals.
Metric #3: Number of kinds of dragonfly and damselfly larvae (Odanata)The number of kinds of dragonfly and damselfly larvae found in dipnet and bottletrap samples tends to be higher in healthier wetlands.  These insects are predators at all stages, and have somewhat longer life cycles than other invertebrates.  Dragonflies pump water in and out of their posterior end, which could expose them to pollutants.  Some odonates lay their eggs on stems of aquatic plants, so if the plants are lost, they lose their egg-laying sites.

Metric #4: Number of kinds of mayfly and caddisfly larvae plus the presence of dragonfly larvae and fingernail clams

Mayflies, caddisflies, and fingernail clams are sensitive to pollution.  Mayflies and caddisflies are gill breathers, allowing them to take in pollutants directly from the water.  Fingernail clams filter small particles from the water, allowing direct intake of pollutants, but also making them more vulnerable to siltation in the water.
Metric #5: Number of kinds of snailsMost snails in wetlands are lunged (pulmonate), meaning they are air breathers.  Sometimes you will see snails hanging upside down under the surface film.  They are breathing and may be feeding on the film.  Snails are herbivores and feed on plants and the algae coating surfaces of plants, sticks and substrates.  The number of taxa of snails is greater in higher quality wetlands than in disturbed wetlands.  Algae and plants can accumulate contaminants, so snails could be exposed to pollutants through their feeding.  Also if the vegetation is lost, there will be less food for snails.

Metric #6: Total number of macroinvertebrate taxa

The total number of invertebrate taxa is usually one of the strongest indicators of the health of wetlands.  The total taxa metric sums the total number of leech taxa, dragonfly and damselfly taxa, snail taxa, and presence of fingernail clams.  In addition, the number of macrocrustacean taxa is added to the total taxa.  These are crustaceans that are visible to the eye.  Smaller crustaceans like water fleas (Daphnia), ostracods and other zooplankters (copepods) are not counted.  The Dipteran or true fly taxa are also included in the total taxa metric.  Mosquito larvae, Chaoborus (the phantom midge), the midges (Chironomidae), the biting midges (Ceratopogonidae) and soldier flies are some examples of some of the Dipteran taxa that might occur in wetlands.


IBI Score Wetland Health Assessment
23-30Excellent
15-22Moderate
6-14Poor

Review the vegetation metrics:
The metrics (measures) listed below are used to assess the health of wetlands.  Each metric receives a score of one, three, or five.  The seven metrics are then totaled to produce an overall IBI score.  The greater the score, the greater the indication of a healthy wetland.  The score is then interpreted into a general health rating of Excellent, Moderate or Poor.

Metric #1: Number of vascular plant genera It is a general ecological principle that integrated and stable natural communities have more kinds of organisms (i.e. greater richness").  Based on this principle this metric measures the richness of vascular plant genera within a wetland.
Metric #2: Number o f nonvascular plantsThis metric is similar to metric #1, in principle, but it evaluates the number of a different plant group, the nonvascular plants. Mosses, liverwort, lichens, and macroscopic algae depend on a healthy aquatic environment for reproduction and are extremely sensitvive to changes in this environment.  With the exception of blue-green and filamentous algae, which are not counted in this metric, this group of plants will disappear quickly under stressed wetland conditions.
Metric #3: number of grass-like plantsThis metric is similar to metric #1 in principle but it measures the diversity of a more specific type of vascular plants, the grasses and grass-like plants.  Grass-like plants are very common and important in wetland communities.  A variety of grass-like plants may grow in a wetland, or it may be dominated by only one or two species. A healthy wetland will typically support several grass-like plants.
Metric #4: Cover of SedgeSedges are one of the grass-like plants and are very important components in the wetland community. Sedges are especially sensitive to changes in wetland hydrology.  This metric score is based on the extent of sedge cover within the sample plot.  The greater the extent, the higher the score.
Metric #5: Presence of BladderwortBladderwort (utricularia) is a carnivorous plant that feeds on micro-invertebrates. As such, its presence or absence is indicative of stress to both wetland plants and animals.  The presence of bladderwort in a wetland suggests good health.
Metric #6: Cover of 'aquatic guild' plantsNearly all of the true aquatic plants depend on an aquatic environment to survive. Many of these plants float or are just below the water's surface. They are especially sensitive to the quality of the aquatic environment.  This metric evaluates the cover of the true aquatic plants. This higher the cover, the healthier the wetland.
Metric #7: Cover of plants with persistent standing litterThis metric measures the cover of certain plants whose annual leaves and stems decompose very slowly after senescence. A high cover of these plants means slower nutrient cycling and lower diversity of both wetland plants and animals. A low abundance of these plants suggests rapid nutrient and mineral cycling and therefore a healthy wetland.


IBI Score Wetland Health Assessment
26-35Excellent
16-25Moderate
7-15Poor