Researchers are putting hard science into the assessment of the impact on waterways of acid mine drainage, in work tackling one of the biggest environmental problems facing the Australian mining industry today.
The scientists have come up with novel indicators for the problem, which costs the Australian mining industry $60 million a year in preventive or site remediation measures. These indicators are the lowly plants and animals at the bottom of the food chain, including bacteria, algae, diatoms (microscopic plants), insects, and crustacea.
Researchers at ANSTO, Adelaide University, Flinders University, The University of NSW, the University of South Australia and the Australian Water Quality Corporation, have been studying the state of waterways around the disused Brukunga iron pyrite mine.
The mine lies in the catchment of Dawesley Creek in the Adelaide Hills.
ANSTO is coordinating the work, which forms part of its Managing Mine Wastes Project. The scientists wanted to quantify the ecological impact of acid mine drainage on Dawesley Creek, and set environmental goals for a remediation program.
Since Dawesley Creek, part of the Bremer River system, is also affected by a sewage treatment plant and salinity, the team broadened its study to include the impact of nutrients and salt.
Acid mine drainage occurs when acid and associated dissolved metals are transported by rainwater into waterways from waste rock dumps and tailings storage facilities on mine sites. The problem is confined to sulfidic ores, which oxidise to sulfuric acid and metal sulfates.
The impact on aquatic life often has been devastating. The mining industry in recent years has taken steps to ameliorate acid mine drainage, and to remediate sites already affected. But until now, no-one has really known how to measure the effectiveness of the works.
"Some of the environmental goals set in the past have been quite arbitrary," said John Twining, an ecologist in ANSTO's Environment Division.
"A lot of money has been spent by the mining industry to control pollution levels without any means of of determining the success of the works or quantifying the resulting ecological benefits.
"Thanks to the Brukunga research, scientists have a handle on the kinds of stresses that freshwater ecological systems can withstand. The work can also help to diagnose sick rivers and creeks, and set environmental targets for remediation".
Some of the best bioindicators, at least in the temperate zone, are the primary producers and nutrient recyclers - bacteria, algae, diatoms and macro-invertebrates, including insect larvae, small insects, snails and crustacea.
"These organisms play a crucial role in the eco-system in their own right," said Mr Twining.
"But a count of these species also acts as a pathology report for the river system as a whole, revealing the health of organisms higher up the foodchain, including fish, amphibians and birds.
"We can tell from the species present whether the river is being affected by acid mine drainage, sewage or salinity, and how serious the problem is."
He said more conventional bio-indicators, like fish and frogs, were less reliable in highly modified temperate zone waterways like Dawesley Creek, where they were present in low numbers and diversity.
The researchers have produced a computer code called Aquarisk which can be used to predict the likelihood that measured or modelled water quality parameters will have an impact on the aquatic eco-system. The code also indicates the degree of improvement in water quality that is required to achieve acceptable ecological outcomes.
They are to present their findings on November 24 at the Third Brukunga Workshop, at the Australian Water Quality Centre at Bolivar, near Adelaide.