Ecological effects of mine effluents on the South Esk River, North-eastren Tasmania. III. Benthic Macroinvertebrates.

Abstract

The ecological effects of mine effluents on the South Esk River were investigated over 2 years on a 170-km section of the river. Quantitative samples of benthic macroinvertebrates were collected at eight sites (three above the trace metal inflow and five below) using an air-lift sampler. Drifting fauna were also collected in the river adjacent to the point of trace metal inflow and in a tributary entering the contaminated section. As far as 80 km downstream from the source of trace metals; the numbers of individuals and the numbers of taxa were reduced in relation to upstream sites. From the 29 most commonly occurring taxa, three groups have been defined by clustering strategies:

(a) taxa that were abundant at both contaminated and uncontaminated sites (a leptocerid caddisfly and a baetid mayfly);

(b) taxa that were most abundant at sites upstream of the contaminated section of river (two mollusc species, four species of leptophlebiid mayfly and five species of caddisfly);

(c) taxa whose numbers were highest at sites below the source of contamination (six dipteran species, four species of caddisfly, one mollusc species, one amphipod species and one species of water mite).

Factors likely to be important in determining the harmful effects of trace metal contamination in the field include the particular metals under consideration, flow rate and stability of the substrata. There is little agreement between the acute lethal concentrations of metals determined by other workers in laboratory studies and the concentrations found to produce harmful effects in the South Esk River. The multivariate approach proved to be a sensitive means for the detection of trace metal contamination. Thecomposition of the drifting fauna was also altered by the trace metal contamination. Thenumbers of rhyacophilidcaddisflies were higher in the contaminated section of river and those of the baetid mayflies and helminthid beetles were lower.