Paula D’Santos, project officer for the NSW Murray Wetlands Working Group, says the alarm was raised at Bottle Bend, upstream from Mildura, when the lagoon’s pH fell from a healthy seven to a deadly three after it became cut off from the river’s main flow. Fish died in their thousands, the banks were lined with toxic aluminium and manganese salts and the gnarled red gums on its banks began to die. "It is like a scene from the apocalypse. It’s just incredible," Ms D’Santos says.
-University of Adelaide, CSIRO and Wentworth Group scientist Mike Young sees it as a final warning to revive the Murray before it is too late. "Bottle Bend’s nightmare is the first sign we are now changing the River Murray system irrevocably …
"Irrigators and environmentalists both need to be alarmed. This is the time to radically change the way we manage the River Murray system from top to bottom."
NSW’s Tareena Billabong — where acid-sulphate soils have also been found — recently suffered a fish kill that left nine tonnes of fish rotting in the mud. The acid-sulphate problem — caused by nutrient-rich submerged banks being exposed to air for the first time in decades — is already rivalling salinity, overextraction and blue-green algae as threats to the river.
Senior CSIRO scientist Rob Fitzpatrick, who is leading a team looking at acid-sulphate soils, says the problem has been found in large stretches of the river in South Australia around Renmark, Blanchetown and Murray Bridge, as well as in lakes Albert and Alexandrina, near the mouth.
Dr Fitzpatrick says the conditions exist for acid-sulphate soils to form right along the river, but it is occurring mainly in areas that had been inundated for decades but are now slowly drying out. The sulphuric acid is produced when naturally occurring iron pyrite in the river bank — a by-product of decaying organic matter — reacts with oxygen.
The problem can be prevented by raising the water level to reinundate banks. The acidity can be absorbed and counteracted by the slightly basic river water, but toxic metallic salts created during the process are also washed into the main stream.
Raising the water level in South Australia also creates a catch-22. "You might save the river, but then the lakes, which are a much bigger area, might be affected," Dr Fitzpatrick says.