Environmental impact of a major copper mine spill on a river and floodplain system

This study examines the impact on channel and floodplain sediments from the accidental release of metal-contaminated waters from the Lady Annie Copper Mine in northwest Queensland, Australia. The spill-impacted Saga Creek and Inca Creek rise in the upper Lake Eyre catchment, which covers ∼1.2 million km² and is one of the world's last and largest unregulated wild river systems. In contrast to other river systems impacted by mining-related spills, the upper reaches of the study system have no history of metal mining, enabling the consequences of a large spill event to be evaluated for its environmental legacy. The contaminated mine water inundated valuable cattle grazing lands and waterholes, resulting in a record fine of $0.5 (Australian) million in 2012. Total extractable metal concentrations from 101 floodplain and channel samples revealed that copper contamination was the principal element of concern with 43% of channel surface and 31% of floodplain surface samples exceeding the Australian guideline value for sediments. Contamination was restricted predominantly to surface sediments (0-2 cm) within ∼50 m of the top of the channel bank and within the first 5 km of the impacted catchment. Although downstream sediments showed a definitive metal contamination impact from the spill, the legacy risk posed to grazing cattle is considered low. The implication arising from this study is that while a large single pollution spill can have serious short-term impacts on river systems and their use for agriculture, its environmental legacy in the absence of cumulative impacts from repeated contamination events could be relatively small.