Evidence from a survey of macroinvertebrate communities and water quality in the early dry season 2001
Department of the Environment and Heritage, permission from the Department of Infrastructure, Planning and Environment (NT), 2004
ISBN 0 642 54968 0 ISSN 1447-1280
Water quality parameters were determined at fourteen sites on streams in the Darwin area. Aquatic macroinvertebrate communities were quantitatively described at thirteen of these sites.
- Multivariate analysis of macroinvertebrate data identified three groups of sites composed of a group of seven sites, a group of five sites and a group consisting of a single outlier site.
- A large number of chemical and physical environmental variables were examined for correlation with the biological data: eleven variables were found to have a significant correlation with the ordination solution. The variables with the highest correlation coefficients were ionic ratio of calcium and magnesium; the percentage of calcium of total cations and zinc concentration.
- Zinc and other metal concentrations were within national water quality guideline limits with the exception of copper at one site and aluminium. High aluminium levels almost certainly reflect high natural background levels and not anthropogenic influence.
- Levels of all pesticides and herbicides were below detection limits in all samples.
- There is no evidence of gross ecological impairment at any site. However, one site DW-21 (Rapid Creek) is showing symptoms of scouring from increased wet season run-off from the developed residential catchment.
- There was evidence of nutrient enrichment at one site (DW-26, Bee's Creek). This site has the highest number of sensitive taxa (n=9) and the second highest number of taxa (n=60).
- Future monitoring may include additional indicators such as diatom community structure, fish community structure and the occurrence of macroalgae and macrophytes.