Questions have been raised over a lack of evidence that the 2022-23 Murray River floods contributed to South Australia’s devastating algal bloom.
University of Adelaide soil and water scientist Luke Mosley said discharge from the major flooding event played little or no role in creating the harmful bloom.
Appearing before the Senate inquiry into the bloom, Dr Mosley said while a “massive load” of nutrients went into the river and the ocean during the flood, the evidence that it helped to drive the bloom was lacking.
Associate Professor Luke Mosley says the time lag raises significant doubts. (ABC South East SA: Caroline Horn)
He acknowledged there were possibly some links between the two events but that the length of time between them created some doubt.
“Because there was a big time lag between the flood and the onset of the River Murray bloom … that time lag and the high energy mixing out in this coastal ocean here meant it was unlikely that the nutrients were available at the time, certainly in relation to the River Murray flood,” he said.
Dr Mosley told the inquiry he had worked in the Murray River, Lower Lakes, Coorong and coastal waters adjacent to the river mouth for two decades.
Tonnes of carp and other fish washed up on south coast beaches during the 2023 flood. (ABC South East SA: Caroline Horn)
This included working with colleagues from the CSIRO during the flood event, studying and sampling the flood plume as far as 50 kilometres out to sea.
His theory contradicts the South Australian government’s messaging around the bloom, which asserts that the flood was one of three “extraordinary” environmental events that led to the formation of the algal bloom, along with the ongoing marine heatwave and a cold-water upwelling during the summer of 2023-24.
Upwelling occurs when wind blows surface water away and deep, cold, nutrient-rich water then rises towards the surface.
In his submission, Dr Mosley said that in his opinion a large upwelling event and marine heatwave might have been sufficient to trigger this event themselves.
The inquiry has held public hearings in Adelaide, Port Lincoln, Ardrossan and Victor Harbor. (ABC South East SA: Caroline Horn)
Dr Mosley was one of several scientists who appeared before the committee at Victor Harbor to call for increased funding and better ongoing monitoring of the coastal environment.
“The lack of a long-term, marine observation-type program means that you’re always reactive,” he said.
“It’s like: ‘There’s a flood. Now there’s an algal bloom.’ Everything’s reactive.”
Coorong, Lower Lakes and Murray Mouth Research Centre director Alec Rolston also appeared before the committee in Victor Harbor.
He acknowledged there were “conflicting opinions around the causative or contributory aspects” to the bloom, and said further investigations were required to determine the role the flood event had.
The extent of the sediment plume from the mouth of the Murray River on January 1, 2023. (Supplied: Evan Corbett/Flinders University)
Greater investment by state and federal governments was needed for scientists to fully understand the drivers of the blooms, as there would be future occurrences across Australia, Dr Rolston added.
“Climate change is real. It’s happening. It’s happening now, and we’re seeing the impacts of that,” he said.
“We need to invest in the science to make sure that we can undertake that planning to reduce and mitigate the impacts as best we can.”
The committee’s final day of hearings will take place at Parliament House in Canberra on Wednesday, with its report due on October 28.