Ash distribution and metal contents of Lake Illawarra bottom sediments

Abstract

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.

History of metal contamination in Lake Illawarra, NSW, Australia

“…The oldest study of metal concentration profiles in Lake Illawarra cores is by Ellis and Kanamori (1977), who collected samples in the 1970s. Their results agree with later results, and deposition during the subsequent 20 years shifted background values to about 5 cm deeper when Chenhall et al (1994), Payne et al (1997) and Gillis and Birch (2006) collected their cores. A different result, though, was obtained by Chenhall et al (1994) who reported metal concentrations in two cores of 1 m depth.…”

“…The lake is connected to the ocean by a narrow tidal channel approximately 2.4 km long, with a micro-tidal environment and low current velocities resulting in restricted lake-ocean water exchange (Chenhall et al, 1994). This lake was chosen for this study as it is one of Australian estuaries most affected by industries (Chenhall et al, 1994).…”

“…Sediment cores were collected from eight sites in Lake Illawarra based on their proximity to potential metal sources established from previous studies (Chenhall et al, 1994). At each location, two replicate cores were collected in order to obtain average profiles and check that the sediment profiles were not disturbed by collection procedures or by local human activities.…”

“…Metal concentration profiles in sediments have been previously measured in Lake Illawarra (Ellis and Kanamori, 1977;Chenhall et al, 1994Chenhall et al, , 2004Gillis and Birch, 2006), but there is no information about selenium and arsenic concentrations, major elements found in Australian black coals. In addition, these studies used different dating techniques with limited use of proxies for crosschecking data.…”

“…In 2009, it was converted to gas-fired power operation. In addition, Lake Illawarra is at the centre of an area of significant residential development (Chenhall et al, 1994).…”