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• Use of plastic enclosures in determining the effects of heavy metals added to Gulungul Billabong (PDF 354 KB)

About the report

Plastic enclosures placed in Gulungul Billabong were used to investigate the behaviour of heavy metals added to billabong waters. One metre diameter enclosures were apparently too small because they did not simulate the dissolved oxygen profiles observed in the billabong. Three metre diameter enclosures were better, showing dissolved oxygen and temperature profiles which were similar to those in the billabong.

Heavy metals added to one of the large enclosures caused observable changes in the algal populations. There was, however, considerable uncertainty about which changes were brought about by the added metals and which were due to natural causes.

The added heavy metals, manganese, zinc and copper, were all rapidly lost from the water column to the sediments. The manganese was reduced to ambient levels in approximately 10-15 days while the zinc and copper concentrations were reduced less rapidly but were near ambient concentrations by the end of the four-week study. The loss of heavy metals was mainly by association of the added ionic metal with particulate matter, which then settled out.