1. Working with a partner, take an approximate 500 ml sample of the water including the debris.
2. Pour a portion of the sample into a petri dish and examine it under low power on the microscope.
3. Using the identification charts, count and identify 100 macroinvertebrates. Try not to hunt for only the large ones or your sample will be biased. If you can not find 100 macroinvertebrates in your sample, take an additional 500 ml sample. Continue this procedure until you and your partner have counted and indentified 100 macroinvertebrates.
4. Identify and count the numbers of each type of organism listed below.
5. Multiply the number of each type by its biotic value.
6. Add up all the numbers and divide by 10. This gives the Biotic Index Value. Check the Biotic Value chart at the bottom of the page to determine the quality of your water sample.
7. Compare your group value with the class values. Do they agree? Why or why not?
||Midge fly larva||
|Black fly larva||
|25 mayflies||25 x 10 = 250|
|15 caddisflies||15 x 10 = 150|
|20 stoneflies||20 x 10 = 200|
|20 scuds||20 x 6 = 120|
|20 midge larva||20 x 5 = 100|
|Total||= 820 / 10 = 82|