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30 July 1998 |
Ref 98/181 |
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The swagman's ghost would be aghast. The future of one of the great symbols in Australia's best-loved song, Waltzing Matilda, is at risk.
The coolibah, like many trees that adorn the Australian landscape, depends on underground water to keep it alive through the dry season. If the water is taken away, is polluted or turns salt, the trees will die.
Groundwater, according to scientists from CSIRO Land & Water, may be the most important element still to be fully factored into how we care for our landscape. This is emphasised in a new report for the Land and Water Research and Development Corporation by CSIRO and Sinclair Knight Merz.
"The role of groundwater in supporting ecosystems across the continent is still poorly understood - yet we know in many cases it is absolutely vital," says CSIRO's Dr Tom Hatton.
"Federal and State Governments have agreed that part of all water should be allocated to the environment. But much of the Australian environment depends on underground water. The trouble is, we don't know how much or to what extent."
The Banksia woodlands of Western Australia's coastal plain rely totally on the water their roots tap, metres below. "You don't see water standing around in pools on the surface, but if you took away the groundwater, or even changed it a little, the trees would die," Dr Hatton explains.
The mound springs of the Great Artesian basin are a famous example of a precious ecosystem at risk due to human activity. Bores used for watering cattle can lower the pressure so much that natural springs dry up, causing all the life they support to die.
The mound springs not only contain rare and even unique plants, animals and fish, they are also part of aboriginal cultural heritage and are important attractions to the growing Outback tourism industry.
"Many Australian rivers, which appear dry on the surface, continue to flow underground - and the trees, vegetation, bird and animal life all depend on this," Dr Hatton says.
About half the flow of the rivers running off the Great Divide comes from underground water. In the North, groundwater is just as important, keeping rivers such as the Alligator, Mary and Gulf country flowing through the dry season. In Central Australia, where surface rivers soon vanish, underground water is more vital still.
"Most of our rivers are continually recharged by underground water, and it is this slow movement of water through the landscape which allows many of our ecosystems to survive and flourish, even when there has been no rain for weeks or even months.
"For instance, if we harvest all the surface water that runs into the Cooper Creek in Central Australia, we will eventually destroy those magnificent stands of red gum and river gum further downstream which depend on the water after it goes back underground."
Dr Hatton's report identifies four kinds of ecosystem which are especially reliant on groundwater:
- wetlands and "damplands", where groundwater comes close to the surface
- woodlands and bush which rely on diffuse, shallow groundwaters moving across the landscape to keep them lush
- the "base flow" or dry-season flow of rivers, about half of which is supplied from underground sources and which determines the character of their ecosystems
- underground aquifer and cave systems, which often contain forms of life and biological processes new to science.
Human activity affects these systems in various ways. We pump out groundwater for farm, industry or domestic use - so depriving the landscape. We pollute underground water by leaking oils, industrial chemicals and pesticides into it. And we cause salinity or waterlogging by adding so much water to one place that it rises to the surface and poisons or drowns the vegetation.
"The message of this report is that we need to wake up to how we manage and use our groundwater, because of the effect this has on the total Australian landscape," Dr Hatton says.
The report recommends that groundwater-dependent ecosystems be recognised as a key part of all future water allocation processes in Australia. Plans to tap groundwater should involve an assessment of the vulnerability of the landscapes that depend on it.
The report also calls for a national way to assess how dependent certain ecosystems are on groundwater, and hence, a national policy which defines what impacts are acceptable or unacceptable.
It calls for an agreed national criterion, such as base flow, to be adopted for comparing different catchments, and an assessment of all major rivers to try to establish how much of their flow comes from underground water.
"The classic Australian image is of a swaggie under a gum tree beside a billabong. Those gum trees depend on groundwater to keep them alive through the dry season. Lower or change that groundwater and you kill the trees. You run the risk of killing an emblem of Australia we have held since Waltzing Matilda was first sung."
More information:
Dr Tom Hatton, CSIRO Land & Water 08 9333 6208
Margaret Bryant, CSIRO Land & Water 08 9333 6215
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