Quantitative Ecological Risk Assessment of the Magela Creek Floodplain in Kakadu National Park, Australia: Comparing Point Source Risks from the Ranger Uranium Mine to Diffuse Landscape-Scale Risks

ABSTRACT

The Ranger uranium mine is surrounded by the World Heritage Kakadu National Park, Australia, and is upstream of the Ramsar-listed wetlands of the Magela Creek floodplain. We present the results of a Quantitative Ecological Risk Assessment (QERA) for the floodplain that combines both point source mining risks and diffuse non-mining landscape-scale risks. A high level of protection for the biodiversity of aquatic ecosystems was used as the assessment endpoint. Mining risks in the surface water pathway were assessed for four key mine-associated solutes (uranium, manganese, magnesium, and sulphate), and non-mining landscape-scale risks were assessed for weeds, feral pig damage, unmanaged dry season fire, and saltwater intrusion from potential sea-level rise due to climate change. Results show that non-mining landscape-scale risks are currently several orders of magnitude greater than risks from mine water contaminants. A weed (Para grass; Urocloa mutica) is the major ecological risk because of its extent, effect, and rapid spread rate. The QERA was incorporated into a Bayesian Belief Network to help evaluate different management strategies. We conclude that non-mining landscape-scale risks to the floodplain should receive the same level of close scrutiny and investment as that applied to uranium mining risks.

Key Words:

• ecological risk assessment
• Ranger uranium mine
• landscape-scale risks

ACKNOWLEDGMENTS

We thank the past and present ERISS (Supervising Scientist Division, Department of the Environment, Water and the Arts) staff, in particular Max Finlayson, Dave Walden, James Boyden, Chris Humphrey, Maria Bellio, Arthur Johnston, and David Jones; Alligator Rivers Region Technical Committee members, in particular former Chair Barry Hart for his support and encouragement, and Keith Hayes (CSIRO Mathematical and Information Sciences) for providing valuable advice; past and present Kakadu National Park ranger staff, in particular Steve Winderlich, Anne Ferguson, and Sally-Ann Atkins; and Kakadu Traditional Land Owners Peter Christophersen, Sandra McGregor, and Violet Lawson for their continued support and advice. We thank Olivier Thebau (CSIRO Marine and Atmospheric Research, Resource Economics Team) for advice on environmental economics. The former ERISS Landscape Program undertook this work, which was recommended to the Australian Government by the Independent Science Panel (ISP) of the World Heritage Committee (WHC) to help differentiate mining and non-mining risks.

Notes

HERA Editor: Billabong—a usually dry streambed that is filled seasonally.