Alana Mackay
Heavy metal transportation, storage and alteration in the Leichhardt River, Mount Isa, Queensland.
Project overview
This project examines sediment and water quality and associated seasonal fluxes in the upper reaches of the mineralised ephemeral Leichhardt River system above and below Mount Isa City, north-west Queensland. Previous research has indicated that historic mining practices have contaminated the Leichhardt River system with Zn (Taylor and Hudson-Edwards, 2005) and other trace metals such as Pb, Cu, Cd, Mn and Fe (Taylor and Hudson- Edwards, submitted), however the extent, mobility and pathways of these metals is currently unknown.
The release and storage of sediment-associated metals into ephemeral rivers is not only poorly researched but presents a unique remediation and management problem that requires detailed spatial and temporal assessment in order to maximise the environmental outcomes from catchment rehabilitation works. Sediments and metal rich waters exposed to high evaporation rates such as those experienced in the Leichhardt River can accelerate the precipitation of metals and various associated compounds including Fe oxides, hydroxides and oxhydrosulphates, which are known to sequester sediment-associated metals. Consequently, contaminants that accumulate in ephemeral pools and slackwater deposits are not only subject to oxidation and significant temporal alteration of important variables such as pH and redox, due to evaporative processes, but are also vulnerable to physical mobilisation during wet season floods. Once mobilised metals may be transferred downstream to grazing lands, stored in Lake Moondarra (Mount Isa’s principle water supply) or pools that support native biota during the dry season.
This project will increase our understanding of the distribution and characteristics of sediment-associated contaminants, their actual hazard and potential risk to ecological health in the Leichhardt River system. This research will quantify any potential effects from contaminant fluxes on instream and adjacent urban and agricultural environments as well as the downstream Lake Moondarra. While the outcomes of the project will be used to develop appropriate specific site and/or river reach remediation and mitigation strategies they will be framed within a broader water resource and catchment management plan designed to protect and enhance water quality and the health of Leichhardt River and Lake Moondarra water bodies.