Aquatic life in a five kilometre stretch of a unique river system in the Blue Mountains World Heritage Area has been almost wiped out by pollution from a disused coal mine, a University of Western Sydney study has found.
Dr Ian Wright, from the School of Natural Sciences, has recorded toxic levels of the heavy metal zinc in the upper tributaries of the Grose River which flows through the threatened Blue Gum Forest.
The pollution is being discharged from the closed Canyon Colliery - which operated from the 1920s to 1997 - near the upper Blue Mountains town of Bell.
“Groundwater flowing through the mine is picking up contaminants, including very high and unnatural levels of zinc. A horizontal drainage shaft is channelling the polluted water to an opening at the headwaters of the Grose River,” says Dr Wright, who is a post doctoral research fellow.
“Zinc contamination in Dalpura Creek, which feeds into the Grose River, is up to 600 micrograms per litre of water. This is more than 10 times the safe level.
“Just 10 to 50 micro grams of zinc per litre of water is toxic to aquatic life,” he says.
While, the pollution is not toxic to humans it is having a devastating impact on the local ecosystem.
In the research, which has been peer reviewed, Dr Wright found the contaminated water had a smaller variety of aquatic life compared to unpolluted stretches of the river.
“Most of the Grose River is a wild and undisturbed river system teaming with small aquatic animals or macroinvertebrates which form an important link in the food chain,” Dr Wright says.
“However, the biodiversity of the river was significantly reduced where the levels of zinc were high. The varieties of aquatic macroinvertebrates - including insects - in the polluted stretches were slashed by half.”
Dr Wright says in the contaminated areas he found just 20 per cent of the number of animals living in the clean reaches.
“You could almost describe some sections of the upper Grose River as sterile or dead,” he says.
Dr Wright also examined the impact on the river system from the Blackheath sewage treatment plant (STP) which discharges almost one mega litre of treated effluent each day in to Hat Hill Creek, a tributary of the Grose River.
Hat Hill Creek below the STP recorded levels of phosphorous more than 100 times the level in non polluted areas, and nitrogen was also more than 100 times normal background levels for the stream. However, the inflow of treated sewage did have one unexpected consequence.
“Macroinvertebrate abundance which declined below the mine contamination site actually increased immediately after the treated sewage entered the river,” Dr Wright says.
“Although the extra water, organic matter and nutrients did improve the food supply for some aquatic life, overall river life in the vicinity of both pollution sources was severely impaired compared to the pristine stretches of the Grose River.”
The Blackheath STP is scheduled to be switched off this year as part of a multi-million dollar environmental upgrade. The sewage which currently enters the upper Grose River will be diverted to more advanced treatment facilities further down the mountains.
Dr Wright is anticipating a major recovery of ecosystem health and water quality in Hat Hill Creek but is also concerned the sudden decrease in water volume and nutrients from the sewage treatment plant could actually intensify the damage to the Grose River.
“Removing almost one million litres of treated sewage water a day from the river system could result in the zinc pollution intensifying and spreading further downstream. The contaminated mine water is a permanent toxic spring, so the only way to stop the damage would be to treat or redirect the polluted water,” says Dr Wright.
