Trace elements and organic matter in a pristine environment: Bathurst Harbour, Southwestern Tasmania

Bathurst Harbour and Macquarie Harbour are estuarine systems on the west coast of Tasmania, Australia. While Macquarie Harbour is grossly polluted from mine operations via contamination of the King River, Bathurst Harbour is surrounded by World Heritage wilderness and is essentially free of anthropogenic influences. The vegetation of the catchments of both harbours is similar and the waters of both harbours are deep brown due to the presence of humic substances. A hydrographic survey of the pristine Bathurst Harbour estuarine system was carried out over 4 days in January/February of 1990 (Austral Summer). Sampling and laboratory analyses for a range of trace elements (Cd, Co, Cu, Fe, Mn, Ni, and Zn) were made using non-contaminating procedures. The concentrations of dissolved cadmium (0.02-0.06 nM) and nickel (2.4-4.9 nM) were essentially the same as the total reactive concentrations. A significant fraction of copper and zinc was associated with particles since the concentrations of dissolved copper (2.2-3.7 nM) and zinc (6-45 nM) were often less than the concentrations of total reactive copper (2.7-6.7 nM) and zinc (10-58 nM). The concentrations of copper, cadmium and nickel were comparable with levels in open-ocean seawater. Total reactive concentrations of iron and manganese were very high in the rivers entering Bathurst Harbour (7900 and 124 nM, respectively) and a large fraction of these metals was associated with particulate matter particularly as the salinity increased. The lowest concentrations of iron and manganese were found in filtered waters at salinity (S)approximate to 35 (31 and 10 nM, respectively). The large amounts of organic matter draining into the estuarine system have fixed ratios between the fractions: dissolved organic carbon, humic substances, and copper-complexing capacity. This implies that it may be possible to estimate the copper-complexing capacity from a simple measurement of light absorbance. The copper-complexing capacity is a measure of the concentration of organic matter that is able to form strong complexes with copper and its concentration (7-93 nM) was in excess of the total concentration of copper in all samples from this survey. Comparison of results from this survey, with those from Macquarie Harbour in the summer of 1989, provided a clearer assessment of the effects of mining operations on trace metal concentrations in Macquarie Harbour.