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Fate of heavy metals in the Magela Creek system, northern Australia: I Experiments with plastic enclosures placed in Island Billabong during the 1980 Dry season - heavy metals

Technical Memoranda 13
Hart BT, Jones MJ and Bek P
Supervising Scientist, 1985
ISSN 0810-9532
ISBN 0 644 01305 2

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Fate of heavy metals in the Magela Creek system, northern Australia: I Experiments with plastic enclosures placed in Island Billabong during the 1980 Dry season - heavy metals (PDF - 716 KB)

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Two 5 m diameter plastic enclosures were used to isolate parts of Island Billabong so that the processes operating to remove added metals from the water column could be studied. The metals manganese, cadmium, copper, lead and zinc were added to one enclosure; the other enclosure was kept as a control. The changes in metal concentrations were monitored over a six-week period from 6 November 1980. Additionally, an analytical scheme was applied that allowed the total concentration of each metal to be divided into three operationally defined fractions: particulate, ion-exchangeable, and non-ion-exchangeable.

Where valid comparisons could be made, the behaviour of the metals in the enclosure differed from their behaviour in the billabong. Some reasons for these differences have been advanced. The differences, while significant at the very low concentrations found naturally in Island Billabong waters, are not expected to influence the usefulness of the enclosures in providing information on the behaviour of higher concentrations of heavy metals added to this system.

All of the metals added to the enclosure were found to be quite removed from the water column over a period of days. For example, after fifteen days, in excess of 65% of each metal had been removed, presumably to the sediments and the epiphytic growth that had built up on the walls of the enclosure. Study of the changes in the speciation of the added metals provided considerable insight into the mechanisms by which these metals are removed from the water column. The main pathways for the removal of each metal are discussed. The behaviour of manganese is believed to have significantly influenced the rapid removal of the other metals. We have postulated that particulate, and possibly also colloidal, forms of MnO_x are formed by the slow oxidation of manganese(II), and that it was these colloidal and particulate surfaces that influenced the behaviour of the other added metals.