Metric #1
Number of kinds of leeches
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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.
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Metric #2
Corixidae proportion metric
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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.
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Metric #3
Number of kinds of dragonfly and damselfly larvae (Odonata)
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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.
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Metric #4
Number of kinds of mayfly and caddisfly larvae plus the presence of dragonfly larvae and fingernail
clams
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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.
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Metric #5
Number of kinds of snails
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Most 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.
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Metric #6
Total number of macroinvertebrate taxa
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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.
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Wetland Health Assessment |
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