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By Alex Kirby
BBC News Online environment correspondent
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Once a wetland, now a saltpan
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Large parts of Australia face a problem from rising salt levels, putting farms, drinking water, and rivers at risk.
The trouble dates from the introduction of European crops, whose shallow root systems did not reach the water table.
As a result, water levels slowly rose, bringing with them old salt deposits which are gradually poisoning the land.
Australians are increasingly divided on how to tackle
the threat, whether by trying to flush the salt out to sea or by
stopping it entering the rivers.
Eaten away
BBC Radio 4's environment programme Costing the Earth went to Australia to see the damage the salt is doing.
Too much salt is bad for emus and other wildlife
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It reports on the way railways, roads and gas pipelines
are all succumbing to corrosion, and says it is estimated that by 2050
there will be no water fit to drink in one of Australia's largest
cities, Adelaide.
Outside the cities, huge tracts of the most productive
farmland are being choked by the salt. The 13.7 million hectares (33.85
million acres) of agricultural land that are likely to be threatened by
the middle of the century will exceed the current total area devoted to
wheat, Australia's principal crop.
Already, waterholes used by Aboriginal people are
contaminated, sheep are being killed by the salt, and some of the great
wines of the Barossa Valley have been put at risk.
River conundrum
One of the most serious consequences of the salt's inexorable rise is its incursion into waterways.
Farmers look for signs of salt
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The Murray river provides the water to grow 40% of
Australia's food, as well as the drinking water for most of the
southern part of the country. But it has become so saline that it is
slowly dying.
There are solutions: many farmers are now planting tree
and bush species native to Australia, as their root systems reach
further down and do not draw up the salt.
Tougher wheat
That is not an option for the arable farmers of the wheat belt, but even for them there may be an answer.
The government research agency, the Commonwealth
Scientific and Industrial Research Organisation, is breeding new
varieties of wheat, modern strains crossed with ancient Persian wheats,
which are being tested to see how salt-tolerant they are.
But there is no unanimity on how to revive rivers like
the Murray. One proposal is to increase the river's flow, so as to wash
more of the salt out to sea.
Against that, another school of thought argues that it
makes more sense to try to prevent the salt leaching into the river in
the first place.
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