||From February to July, 2003 macroinvertebrate samples were collected from four sites in the lower Murray River and Lake Alexandrina region to determine the effects of low water levels on macroinvertebrate community structure. The four sites investigated were Wyndgate Channel on Hindmarsh Island, Clayton Lagoon, Milang and Walker Flat. Samples were collected by the Department for Environment and Heritage and delivered to the Australian Water Quality Centre for identification and analysis. The macroinvertebrate data was assessed using the autumn edge AusRivAS computer predictive model and multivariate statistical techniques.
Samples were collected according to the AusRivAS (Australian Rivers Assessment System) sampling protocol which involves sampling a 10m stretch of river using a dipnet with a 250 micron mesh. Samples were initially preserved with 75% ethanol in the field, with formalin being added to the samples once they had been delivered to the Australian Water Quality Centre. Conductivity, pH, dissolved oxygen, water temperature and turbidity were recorded at all sites at the time of sampling. Macroinvertebrate samples were collected at four sites on a monthly basis from February to July 2003.
From the 24 samples collected in this study a total of 114 macroinvertebrate taxa were identified. Dipterans (true flies) were the most diverse group of organisms collected with 26 different taxa recorded. Ten taxa each of caddis flies, true bugs and crustaceans and eight aquatic beetle species were collected. The highest number of taxa collected in any one sample was at Milang in February with a total of 36 collected. The lowest number of taxa (19) was collected from Clayton Lagoon in June. Six species of fish and 22 zooplankton taxa were collected during the study.