Water bugs - indicators of stream health
Article by Gordon Agnew, senior waterways officer, Sunshine Coast Council
Council’s waterways and catchment team recently facilitated a macroinvertebrate workshop with 39 Peachester State School students at Annie Hehir environmental reserve.
Aquatic macroinvertebrates are small animals that live for all, or part, of their lives in water. Some of the different types of macroinvertebrates discovered on the day included dragonfly larvae, mayfly nymph, caddisfly nymphs, freshwater shrimp and whirlygig beetles.
Some of these are sensitive to pollution whereas others can live in polluted waters. Because of this variability in the sensitivity to pollution, macroinvertebrates make good biological indicators. By sampling macroinvertebrate communities and looking at both the types and numbers of animals present we can get an idea on the health of the waterway.
A healthy waterway will have a large number of different types of macroinvertebrates present with no one type dominating the system. A polluted waterway will only have a few different types of macroinvertebrates present and generally include things like aquatic worms, water fleas and non-biting midge larvae.
Sampling water quality on its own to assess river health gives us a good idea as to what contaminants are present in the waterway at the time of sampling. What it doesn’t tell us is whether these contaminants are having an impact on the waterway and, if so, to what extent. Looking at the macroinvertebrate communities can give us a much better understanding of the overall impacts that any contaminants are having on the waterway.
Assessing macroinvertebrates can be done in a number of different ways such as using the AUSRIVAS (Australian River Assessment System) models, using pollution grading systems such as SIGNAL (Stream Invertebrate Grade Number Average Level) and looking at community structure and complexity.
For more information:
- Western Australian Department of Water and Environmental Regulation.