Indicator species (source; Wikipedia)
An indicator species is any biological species that defines a trait or characteristic of the environment. For example, a species may delineate an ecoregion or indicate an environmental condition such as a disease outbreak, pollution, species competition or climate change. Indicator species can be among the most sensitive species in a region, and sometimes act as an early warning to monitoring biologists.
Monitoring the environment using indicator species is called biomonitoring.
Insect larvae such as Mayfly and Stonefly larvae are not tolerant of low oxygen levels in water. They are therefore good indicators of clean, unpolluted water. Organisms like flatworms or sludgeworms on the other hand absorb oxygen directly through the skin and can tolerate much lower oxygen levels.
Unpolluted streams also have a greater variety of possible niches for species to exploit and therefore have a greater diversity of invertebrates (and vertebrates) living in them.
Other factors may also affect the numbers of indicator species, e.g.
water turbulence - white water is well oxygenated
vegetation in the water, e.g. tree roots, weed, etc.
bedload - boulders, pebbles sand or gravel
speed of flow
Choose one of the factors above and investigate its effect on the type, number and diversity of invertebrates present
Ethics of sampling using live animals.
Animals should be handled carefully to minimize damage/deaths and should be returned unharmed to their habitat as close as possible to the point where they were removed.
Equipment; kick sampling nets, plastic trays, hand lenses, keys to invertebrates.
Plan your investigation.
Choose at least 2 sample points with different flow rates.
Kick sampling needs to be done facing down-stream.
Kick the river bed gently and hold the net on the bottom a few cm downstream of where you are kicking. In still or very slow moving water sweep the net through the area disturbed by kicking.
Shuffle forwards and continue collecting for 60 seconds (count or use a timer).
Empty the net into a plastic tray containing 1 cm depth of water.
Remove stones or vegetation after inspecting it for invertebrates.
Use the key to identify invertebrates and count them. Record your results in a table.
You are trying to say which species and how many of each species are present.
Measuring stream flow rates. Measure 2m in the direction of flow. A person releases a tennis ball, orange or other floating object at the upstream end and starts the stop watch. The watch is stopped when the ball reaches the person at the downstream end of the 2 m. Speed is distance (2m) divided by time in seconds (m/s). Repeat 4 times, disregard any obviously false results (e.g. the ball gets stuck in an eddy) and calculate a mean.
You can also use the analysis recording form to estimate the pollution levels in the stream.