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

ReportNo WSAA 126

October 1997

SYNOPSIS

Undersome conditions it becomes necessary to operate emergency relief structures,overflow control mechanisms, within the sewerage system to prevent problemsassociated with overloading of the system downstream. Apart from the humanhealth risks, the impact of sewage overflows on aquatic ecosystems mayjeopardise the long-term health of our waterways.

Freshwatermacroinvertebrates have been found to be a useful tool for determining thebiological condition of aquatic systems. In this investigation, the impact ofthree stormwater drains with different discharge characteristics on themacroinvertebrate community composition of a section of Darebin Creek, an urbanstream, was monitored between February and August 1995.

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

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

Theresults showed that the drains had quite different characteristics from thecreek itself, and that Darebin Creek is suffering from moderate to high organiclevels increasing along the length of the stream. The change inmacroinvertebrate fauna between the above drain sites and below drain sitesdemonstrated that all drains were contributing to the level of instreampollution.

Seasonaldifferences were evident, and site also had an impact, with species number anddiversity decreasing along the length of the stream. A general deterioration inthe biological community down the length of the stream was indicated.

Moreextensive sampling around the time of discharges, and further research into thebiology of the species present is needed to further identify indicators capableof distinguishing the impact of the drains. Further investigation into themacroinvertebrates rather than the diatoms is warranted as the diatoms failedto demonstrate any significant differences between the creek sites. Other typesof indicators may also be worth investigating such as the impact of thedischarges on structural abnormalities in certain species.

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