A survey of aquatic macroinvertebrates in lentic waterbodies of Magela and Nourlangie Creek catchments, Alligator Rivers Region, NT
Internal Report 225
O'Connor R, Humphrey C, Dostine P, Lynch C & Spiers A
Supervising Scientist Division
Department of the Environment, Water, Heritage and the Arts
About the report
Aquatic macroinvertebrates were sampled from the littora of seven lentic waterbodies of Magela and Nourlangie Creek catchments over a 5 week period from May to June 1995. Four of the waterbodies occurred on the project area of the Ranger Uranium Mine (RUM), three of which were contaminated to varying degrees by mine-waste waters. Waterbodies not directly draining the Ranger mine site had generally higher taxon (family) richness than those draining the mine site. Thus, greatest overall taxon richness was recorded in Georgetown Billabong in Magela Creek catchment whilst Buba and Sandy billabongs, control waterbodies in Nourlangie Creek catchment, had on average, the highest number of taxa per site. Least overall family richness was found in Djalkmara Billabong while, on average, this billabong together with Coonjimba Billabong (both in Magela Creek catchment and draining the mine site) shared the least number of taxa per site. Multivariate analysis of community structure ordinated waterbodies along a gradient that was significantly correlated with electrical conductivity. Taxa that were correlated with the ordination space, and lying in the same direction as electrical conductivity, were dytiscid Coleoptera and mesoveliid Hemiptera which may be tolerant of high conductivity, metal-enriched waters. Comparison of the ordination of species-level data for chironomids and that incorporating all macroinvertebrate families showed a similar gradient correlated with conductivity, overlain by differences among and within waterbodies most likely associated with physical features of the habitat. Collectively, these results may indicate that invertebrates have responded to mine-related disturbance though further studies are required to draw greater inferences from the data.
In a related study, patterns of microinvertebrates in the waterbodies were shown to be related to the 'physical type' of waterbody - artificial versus natural. This contrasts with the water quality gradient observed in the present study. Thus, if macroinvertebrate community structure is in fact altered by contamination arising from mine-waste waters, as suggested in our data, it would make this assemblage a useful one to monitor and assess mining impact upon aquatic ecosystems downstream of the Ranger mine.