LAST week’s ABC’s Catalyst science program on the effect of urban run-off in Brisbane waterways has generated renewed calls for remedial action from Shoalhaven Riverwatch.
On the program, University of Queensland Associate Professor Greg Skilleter showed the effect that increased nutrients such as nitrogen and phosphorus had on organisms living in the mangrove areas lining Moreton Bay.
When nutrient enriched algal blooms decompose, oxygen is extracted from the water affecting the survival of organisms.
Excessive algae growing on seagrass beds can cause widespread damage, converting the area to lifeless mudflats.
The Healthy Rivers Commission said a decade ago that more than half of the Shoalhaven catchment was under high environmental stress.
The Commonwealth-funded National Land and Water Resources Audit (2001) indicated the nutrient load on the Shoalhaven River to have tripled since pre-European times. The same audit described the health of invertebrates in the river as “severely impaired” downstream from Bamarang.
The Australian River Assessment System labels the Shoalhaven River as “substantially modified based on the nutrient and suspended load index”.
Riverwatch vice president Charlie Weir said nutrients were building up in Shoalhaven River because of the lack of fresh water being released from Tallowa Dam.
He pointed to the accumulation of slime on riverbanks and young mangroves on Numbaa Island
“It’s dragging all the young mangroves down,” he said. “It’s killing all the seagrass.”
Some of the nutrient load comes from the Nowra and Bomaderry sewerage plants. They are licensed to emit a total of 50 tonnes of nitrogen and 25 tonnes of phosphorous into the Shoalhaven River each year.
Shoalhaven City Council Environmental Services Manager Kellie Lowe said that, historically, council had focused on testing the river for public health
However, this focus has incorporated ecological health over the past decade to include measurement of nutrients and algae.
Ms Lowe said council had initiated a Clean Water Model in partnership with community, government and university interests to reduce pollutants to the river.
This included risk assessment of pollutant sources, capital works in sewerage plants and lifting the level of scientific study of the river itself.
Ms Lowe is seeking funding from DECC to improve environmental monitoring capability.
“We have limited resources and budget,” she said.
Riverwatch volunteer John Tate said volunteers continually removed algae from young mangrove seedlings to ensure their survival.
He called for support from the Southern Rivers Catchment Management Authority (SRCMA) and Shoalhaven City Council.
“It would be good if the authority or council could fund Associate Professor Greg Skilleter to come to Nowra and have a look at the slime here”, Mr Tate said.
SRCMA Chairperson Pam Green said the authority had worked in partnership with Riverwatch to analyse the slime, but that further investigation was needed.
“We’re aware of the issue in the Shoalhaven River,” she said.
“We would encourage the Department of Environment and Climate Change (DECC) and Shoalhaven City Council to take a proactive approach.”