HR: 0800h
AN: H51B-0467    [Abstracts]
TI: Seasonal Fluxes and Cycling of Trace Metals in Semi-Arid Fluvial Systems: Leichhardt River, Queensland, Australia
AU: * Mackay, A K
EM: amackay@els.mq.edu.au
AF: Department of Physical Geography, Macquarie University, Department of Physical Geography, Macquarie University, Sydney, NSW 2109, Australia
AU: Taylor, M P
EM: mark.taylor@mq.edu.au
AF: Department of Physical Geography, Macquarie University, Department of Physical Geography, Macquarie University, Sydney, NSW 2109, Australia
AB: This paper examines the storage and transfer of trace metal contaminants in water and sediment within the upper Leichhardt River Catchment (1,113 km2), Mount Isa, north-west Queensland. The Leichhardt River runs adjacent to Mount Isa City and the Cu and Pb-Zn-Ag Mount Isa Mine and smelter (MIM) and feeds Lake Moondarra, Mount Isa's potable water supply. The river flows only during the monsoonal wet season (December- March) and for the remainder of the year is characterised by a series of disconnected temporary and permanent pools ranging in length from 10 m to 1 km. These pools are significant because they act as storage zones for water-soluble and sediment-associated metals and serve as refugia for native and domestic fauna during protracted intervals between wet season flows. To recognise seasonal fluxes and cycling patterns of trace metal contaminants in the Leichhardt River system this study investigates the physico-chemical water quality of the wet season flows and the subsequent seasonal variations in the dry season pool water. In January 2007 two floods were studied using sixteen rising stage water quality samplers along the Leichhardt River. The samplers were placed above and below MIM, and within selected tributaries draining MIM to ascertain the specific impacts from mining activities on water quality. Grab samples were also collected during the floods and on the falling stages of flow within the river system. Following this, dry season water quality sampling commenced on eleven remnant pools over a period of 8 months. Overall 60 wet season and 34 dry season water samples were collected and analysed for physico-chemical (pH, EC, DO, TDS, SS) variables in the field and total and water soluble cations, trace elements of concern (Cd, Cu, Pb, Zn) and anions via ICP-MS and ion chromatography, respectively. In addition, mineralogical and geochemical analysis was undertaken on 34 bottom sediment samples collected from the pools. Analysis of the temporal metal fluxes revealed two tributaries draining the MIM lease recorded the highest total (King Gully: Cd, 30, Cu, 3600, Pb, 3600, Zn, 4900 ug/L) and water soluble trace metal (Death Adder Creek: Cd, 17, Cu, 780, Pb, 61, Zn, 1500 ug/L) concentrations during the wet season flows. Concentrations were highest at the onset of the floods and although values decreased during the rising limb of the hydrograph, total and water soluble contaminants remained elevated with respect to Australian Government Guidelines and pose a potential environmental toxicology risk. Monitoring of the dry season pools commenced in February 2007 and showed highly variable water soluble trace metal concentrations ranging from below instrument detection to 140, 12, 12 and 7 ug/L for Zn, Pb, Cu and Cd, respectively. The highest concentrations were recorded towards the end of the dry season and within the pools adjacent to and downstream of the MIM lease. The results indicate that metal contaminants are predominately particulate bound during wet season flow and are removed from suspension upon capture and storage in Lake Moondarra and channel pools. The pool waters became more concentrated with soluble metal contaminants over the dry season and were controlled by evaporation and reduced pools size. Overall, sediment and water quality in the Leichhardt River and tributaries draining the MIM lease is seriously impaired with respect to Australian Government Guidelines. However, while it is clear that a potential environmental toxicology risk exists there remains an absence of ecotoxicological data examining the effects of metal contaminants on the biotic occupants of the system.
DE: 1806 Chemistry of fresh water
DE: 1831 Groundwater quality
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: 2007 Fall Meeting