Zinc in the sediments, water and biota of Lake Burley Griffin, Canberra

Zinc concentrations and total amounts in the sediment, water and biota of Lake Burley Griffin were measured to identify where zinc originating from an upstream mine was being accumulated once it entered the lake and to identify potential lake management problems. Estimates were made based on lake wide sampling on a single occasion. Sediments contained most zinc with 4.2 × 105 kg. Of this 11 ± 4% was gut soluble (pepsin released). Water contained the second largest store at the time of sampling with 597 kg of zinc. Estimated lakewide stores of zinc in fish (Cyprinus carpio) macrophytes (mostly Typha orientalis), zooplankton and macroinvertebrates were 144 kg, 1.4 kg, 0.55 kg and 0.14 kg zinc, respectively. Zinc stores in the water and biota will exhibit large changes depending on rainfall and seasonal growth but they will still be small relative to the amounts held in sediments. Comparison of zinc concentrations in surface sediments (561 ± 81 mg/kg) and water (0.018 ± 0.002 mg/kg) with those before remedial works were performed in 1974 to control a metal contamination source upstream at Captain's Flat show that there has been a reduction in the levels of zinc recorded in the lake (pre-1974 sediment, 1109–1670 mg/kg; water, 0.1 mg/kg). Concentrations of zinc in lake water were well below those reported to be toxic to phytoplankton, zooplankton and fish or to cause degeneration of gill structures. Levels of zinc in fish are below the Australian National Health and Medical Research Council's recommended maximum levels for human consumption. Examination of the oxygen status of Lake Burley Griffin indicates that zinc release from lake sediments under reducing conditions is unlikely to be a potential problem. The major source of zinc to the lake is considered still to be from the mine waste polluted Molonglo River with little contribution from other creeks in the catchment.