ASH DISTRIBUTION AND METAL CONTENTS OF LAKE ILLAWARRA BOTTOM SEDIMENTS

The distribution of anthropogenically derived ash and metal contents of Lake Illawarra bottom sediments have shown that elevated concentrations of trace metals, particularly Zn, are linked to ash concentrations. The highest concentrations of total metals (up to 10 times the locally defined background) were recorded from Griffins Bay, adjacent to the Port Kembla industrial complex. Other sites investigated exhibited only slight trace metal enrichment in near-surface sediments, typically 1.4 to 2 times the background. Analytical data from inductively coupled plasma mass spectrometry (ICPMS) indicate that the ratio of EDTA-extractable ratio:total metal present in the sediment generally decreases in the order Pb, Zn and Cu. Lake sedimentation rates, calculated on the basis of metal and ash depth profiles, were found to lie in the range 6.9 to 16 mm year-1 and represent the most serious long-term environmental problem in the Illawarra region.