Effects of trial disposal of acid-iron effluent from titanium dioxide production on the seafloor and epibenthic macroflora offshore from Koombana Bay, Western Australia

The effects of a trial discharge of acid-iron effluent, resulting from titanium dioxide production, on the seafloor and epibenthic macroflora offshore from Koombana Bay, Western Australia, were assessed. Approximately 88,0001 day⁻¹ of effluent containing 28 g l⁻¹ of iron and 137 g l⁻¹ of H₂SO₄ were discharged through a submarine pipeline from February 1976 to December 1977. This amount of effluent, constituting approx. 5% of total production, was intended to provide a guide as to the environmental effects on the seafloor of discharging the total amount of effluent.Preliminary studies suggested that discernible effects of the discharge were likely to be restricted to the immediate vicinity of the outfall. Consequently, surveys of the effects of the discharge were conducted by divers in December 1976 and April and December 1977 within 400 m of the outfall. The parameters measured were iron concentration in the surface sediment, number of macroscopic plant species (algae and seagrass) and leaf characteristics of the seagrass, Posidonia ostenfeldii. Additional observations on iron staining of the sediment and the condition of the macroscopic plants were also recorded by the divers.By December 1976, the outfall was surrounded by a zone, with a diameter of approx. 200 m, which was totally denuded of macroscopic plants. Extending further from the outfall was a zone in which some effects of the effluent (e.g. sediment stained by iron, reduction in macroscopic plants) were discernible. The total area of seafloor discernibly affected by the effluent in December 1977 when this study finished was 16 ha. At that time, the affected area may have still been increasing in size, and thus the figure of 16 ha must be considered only as the minimum area likely to have been affected by the discharge.