What is Benthic Invertebrate Monitoring?

Students from schools in and near the Cedar Creek watershed determine stream health using a method called "benthic macroinvertebrate monitoring."

• Benthic: Bottom of the stream

• Macroinvertebrate: Animals without backbones that are large enough to be seen without the use of magnifying equipment

Some invertebrates can tolerate pollution and others cannot. These invertebrates are called indicator species.

Working in small groups, the class collects and inventories eight samples at each monitoring site. To collect a sample, students kick up the bottom of a riffle area in their site and collect the disturbed gravel and sediment in a D-frame net. This sample is then dumped into a plastic tray. The group looks for invertebrates in their sample and records the number of each type of invertebrate collected on their data sheets. Only live animals are counted: empty snail or clam shells are noted in a site notes section on the data sheet. After the students have counted everything they saw in their sample, the tray is emptied back into the stream.

The health of the sites are determined using a Stream Health Assessment Index developed by the Ohio Department of Natural Resources. This is a qualitative analysis of stream health. The calculation is based on the presence and absence of certain types of invertebrates.

Group 1: Pollution intolerant invertebrates

• stone fly nymph

• may fly nymph

• caddis fly larva

• dobson fly larva

• riffle beetle adult

• gilled snail

• water penny beetle larva

Group 2: Invertebrates that tolerate a wide range of conditions

• dragon fly nymph

• damsel fly nymph

• crayfish

• sowbug

• beetle larva

• crayfish

• crane fly larva

• sideswimmer

• clam

Group 3: Pollution tolerant invertebrates

• aquatic worm

• pouch snail

• leech

• midge fly larva

• black fly larva

Stream Health Assessment Index Calculation

The index is calculated for each sample and averaged for the final site assessment value.

• Group 1 Score = Number of types of Group 1 Invertebrates (maximum 7 types) x 3

• Group 2 Score = Number of types of Group 2 Invertebrates (maximum 8 types) x 2

• Group 3 Score = Number of types of Group 3 Invertebrates (maximum 5 types) x 1

Stream Health Index = Group 1 Score + Group 2 Score + Group 3 Score

The stream health values from the eight samples at each site are averaged to produce the overall site score.

• 23 or more = Excellent

• 17 to 22 = Good

• 11 to16 = Fair

• 10 or less = Poor

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