Development of a Bioindicator to Measure In-stream Effects of Wastewater Overflows

This report was produced for the Urban Water Research Association of Australia, a now discontinued research program.

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Report no. UWRAA 126

October 1997

Synopsis

Under some conditions it becomes necessary to operate emergency relief structures, overflow control mechanisms, within the sewerage system to prevent problems associated with overloading of the system downstream. Apart from the human health risks, the impact of sewage overflows on aquatic ecosystems may jeopardise the long-term health of our waterways.

Freshwater macroinvertebrates have been found to be a useful tool for determining the biological condition of aquatic systems. In this investigation, the impact of three storm water drains with different discharge characteristics on the macroinvertebrate community composition of a section of Darebin Creek, an urban stream, was monitored between February and August 1995.

Diatoms were also examined using artificial substrates, and sixteen water quality parameters were monitored on a monthly basis over the period of the study.

After reviewing the current literature, it was decided that total community composition, rather than dependence on the presence of “indicator species” would be used to assess the condition of the sites sampled.

The results showed that the drains had quite different characteristics from the creek itself, and that Darebin Creek is suffering from moderate to high organic levels increasing along the length of the stream. The change in macroinvertebrate fauna between the above drain sites and below drain sites demonstrated that all drains were contributing to the level of instream pollution.

Seasonal differences were evident, and site also had an impact, with species number and diversity decreasing along the length of the stream. A general deterioration in the biological community down the length of the stream was indicated.

More extensive sampling around the time of discharges, and further research into the biology of the species present is needed to further identify indicators capable of distinguishing the impact of the drains. Further investigation into the macroinvertebrates rather than the diatoms is warranted as the diatoms failed to demonstrate any significant differences between the creek sites. Other types of indicators may also be worth investigating such as the impact of the discharges on structural abnormalities in certain species.

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