Identification sheet
Tick off the macroinvertebrates in the table and then total the pollution index.
Using macroinvertebrates to estimate the health of freshwater
Very sensitive/ caddisfly larva (10)
/ / mayfly nymph(10)
/
Total for very sensitive=
Sensitive
/ water mite (6) / / beetle larva (6) / / dragonfly nymph (4) / / water strider (4)
/ nematode (4) / / whirligig beetle (4) / / damselfly nymph (4) / / amphipod (4)
Total for sensitive=
Tolerant
/ flatworm (3) / / freshwater mussel (3)
/ Total for tolerant =
Very tolerant
/ midge larva (2) / / mosquito larva (2) / / diving beetle (2) / / water scorpion(2)
/ backswimmer (2) / / boatman (2) / / bloodworm (2) / / pond snail (1)
Total for very tolerant =
Pollution index total =
When you reach a total you can work out the health of the stream from the table below.
Pollution index / Health of stream0-20 / poor
21-35 / fair
36-50 / good
more than 50 / excellent
The health of the lake was______.
Method
- Select a place to sample that is easy to recognise and is not dangerous.
- Dip the net through the water and the water plants. Use a long slow sweeping action.
- Search for 15 minutes (use a stopwatch or watch with a timer)
- Fill the ice cream container or tray with water from the lake.
- When you catch any macroinvertebrates place them in this container.
- Look under any rocks in the water, remember to replace rocks.
- Look for organisms on the surface of the water.
- Disturb the bottom of the water to stir up any macroinvertebrates.
- When you have caught some macroinvertebrates separate them into different species (types) using the ice cube tray.
- Identify the species using the Identification sheet on the next page.
- Tick off the macroinvertebrates in the table.
- The pollution index is in the table. Work out the pollution index for the lake.
- Select macroinvertebrates to take back to the lab for microscopic examination.
- When you finish carefully return the other organisms to where you found them.
Science @ the lakes