TRACE-ELEMENTS AND ORGANIC-MATTER IN A PRISTINE ENVIRONMENT - BATHURST HARBOR, SOUTHWESTERN TASMANIA

Bathurst Harbour and Macquarie Harbour are estuarine systems on the we st coast of Tasmania, Australia. While Macquarie Harbour is grossly po lluted from mine operations via contamination of the King River, Bathu rst Harbour is surrounded by World Heritage wilderness and is essentia lly 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 o f the pristine Bathurst Harbour estuarine system was carried out over 4 days in January/February of 1990 (Austral Summer). Sampling and labo ratory analyses for a range of trace elements (Cd, Co, Cu, Fe, Mn, Ni, and Zn) were made using non-contaminating procedures. The concentrati ons of dissolved cadmium (0.02-0.06 nM) and nickel (2.4-4.9 nM) were e ssentially the same as the total reactive concentrations. A significan t 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) wer e 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 ni ckel were comparable with levels in open-ocean seawater. Total reactiv e concentrations of iron and manganese were very high in the rivers en tering Bathurst Harbour (7900 and 124 nM, respectively) and a large fr action of these metals was associated with particulate matter particul arly 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 d raining into the estuarine system have fixed ratios between the fracti ons: 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. Th e copper-complexing capacity is a measure of the concentration of orga nic matter that is able to form strong complexes with copper and its c oncentration (7-93 nM) was in excess of the total concentration of cop per in all samples from this survey. Comparison of results from this s urvey, with those from Macquarie Harbour in the summer of 1989, provid ed a clearer assessment of the effects of mining operations on trace m etal concentrations in Macquarie Harbour.