10 June 1999 - CSIRO Bays & Estuaries Release

Following is a copy of a media release from CSIRO. If you would like further information check the CSIRO website.
 
 

CSIRO Media Release Mr Julian Cribb Phone +61 2 6276 6244 Mobile 0418 639 245 Fax +61 2 6276 6821 Ref 99/124

Our Bays and Estuaries "At Risk"

Many of Australia's 750 major river estuaries and bays are at risk of the sort of ecological collapse that recently turned part of the Gippsland Lakes into toxic "green pea soup", one of Australia's leading environmental scientists has warned.

But the good news, according to CSIRO Land & Water Chief Dr Graham Harris, is that scientists have recently achieved a
breakthrough in understanding of the processes involved in the collapse of coastal ecosystems - and so, better ways to prevent it.

Estuaries, particularly in populous areas of Australia, have undergone a century-long assault from land clearing, erosion,
urbanisation, pollution, nutrient runoff, acid soils, introduced pests, the damming of rivers and dredging of river bars, he says.

The result is that estuaries naturally sparkling clear and full of seagrasses and fish become turbid, dominated by algae - often
toxic - and devoid of native waterlife.

"Our most important recent advance is the discovery there is a point-of-no-return, or hysteresis, where the system flips from one type to the other," Dr Harris explains.

"Once you reach this point, it becomes extraordinarily difficult, if not impossible, to change the estuary back to the way it used to be.

"This means it is of the greatest importance to look at what we are doing on the land in the catchments of our bays and estuaries, and to manage our activities far better - before the coastal ecosystem reaches that point."

This will involve adopting more sustainable farming and forestry methods, curbing urban runoff, effluent and other forms of pollution and reducing the overfishing of estuary fish stocks.

Dr Harris explains that one of the key insights to emerge from research into our estuaries is how we have altered the natural
coastal water balance.

"We have dammed the rivers inland, preventing the periodic flushing which once kept the estuaries clean and fresh. We have cut through river bars, allowing the salt water to push upstream, turning the mildly brackish estuary as salty as the sea.

"This saline water in turn triggers a boom in anaerobic bacteria, which begin to unlock huge amounts of nutrients from the mud.
Salinity and warmth cause layers to form in the water. These still layers and a vast food supply create perfect conditions for algal blooms. Gradually the water body turns stagnant.

"We are seeing this sort of thing quite clearly in the case of the Swan and Canning rivers in WA, and the Gippsland Lakes in
Victoria. There are many other examples all round the coast," he says.

"Once these systems were clear, mainly fresh or brackish water, which was occasionally flushed out by episodes of heavy rainfall. That no longer happens, because we have dammed the rivers and taken the fresh water."

Dr Harris believes there is as powerful a case for using 'environmental flows' to clean out Australia's coastal bays and
estuaries, as there is for using them to maintain our inland rivers and wetlands.

"In Australia, with its low and variable rainfall, flushing the system is incredibly important to maintaining the balance, and preventing it from tipping over the point of no return," he says.

He also warns that suburban canal development round Australia is a potential timebomb for toxic algae, because it has low flushing and high salinity, accompanied by high runoff of nutrients and chemicals. This risk is already evident in established canal
developments in Adelaide.

Much of the new understanding of how coastal ecosystems function was pioneered by CSIRO in the Port Phillip Bay Study,
which attracted international acclaim.

Dr Harris says that, working with the new Co-operative Research Centre for Coastal Zone and Estuarine Water Management
(CRCCZEWM), in association with the National Land and Water Resources Audit, CSIRO is now embarking on a national
assessment of the continent's 750 main estuaries.

The aim is to assess the condition of each, see how many are approaching the point of no return, and what can be done through a national approach to better catchment and water management to save them.

"We have fair idea already that most of the tropical estuaries are still in quite good condition, because they are regularly flushed by the monsoon and have less human population pressure.

"The ones in real trouble are those from Central Queensland south, round the coast to southwest WA, particularly where there is heavy urban and rural development."

A focus of the program will be to look at ways to prevent the overfishing, both professional and recreational, of native coastal fish stocks. The loss of fish is one factor leading to algal blooms, because fish fry are part of the chain that naturally keeps algae in check.

Another aspect is to establish the extent to which introduced pests like the carp, the European fanworm, the green crab and Pacific seastar are causing havoc in estuarine ecosystems, supplanting native sealife and leading to ecological decline.

More information:
Dr Graham Harris, CSIRO Land & Water 02 6246 5621 or 0417 463 158
or
Ms Margaret Bryant, CSIRO Land & Water 08 9333 6215 or 0417 247 241