The health of Australia’s Murray Darling river system, already shockingly poor, has just taken a turn for the worse. In the past month, tracts of wetland at the mouth of the Murray have become as corrosive as battery acid, forming a yellow crust of sideronatrite, a mineral that only forms in extremely acid soil.
The Murray-Darling Basin is 3,375 km long, drains one-seventh of the Australian land mass, and is currently by far the most significant agricultural area in Australia. The name of the basin is derived from its two major rivers, the Murray River and the Darling River.
Total water flow in the Murray-Darling basin in the period since 1885 has averaged around 24,000 gigalitres per year, although in most years only half of it reaches the sea and in dry years much less. Estimated total annual flows for the basin range from 5,000 gigalitres in 1902 to 57,000 gigalitres in 1956.
The Murray-Darling Basin is very important for rural communities and Australia's economy. Three million Australians inside and outside the Murray-Darling Basin are directly dependent on its water. About 85 per cent of all irrigation in Australia takes place in the Murray-Darling Basin, which supports an agricultural industry worth more than $9 billion per annum.
The Murray-Darling Basin is Australia’s most important agricultural region, accounting for over 39 per cent of Australia’s gross value in agricultural production. The range in climatic conditions across the Basin means there is a whole range of agricultural commodities produced.
The Basin has been termed Australia’s agricultural heartland, it’s ‘food basket’, but it is much more than that, as its agricultural output makes a major contribution to the National economy. Agriculture provides the raw materials for most of the Basin’s manufacturing activity, as well as many processing companies beyond the region.
The long-term productivity and sustainability of the Murray-Darling Basin is, however, under threat from over-allocated water resources, salinity and climate change.
This latest indicator of the river’s decline is detailed in reports to be released this week by the CSIRO Land and Water research institute in Adelaide, South Australia. For years drought and mismanagement have reduced water flows in the Murray Darling system , altering salinity, temperature and nutrient levels. But in July last year , a team lead by Rob Fitzpatrick , who wrote the new reports , found a new problem: falling water levels in lakes Alexandrina and Albert at the Murray s mouth in South Australia were exposing the surrounding soils, rich in iron sulphide, to the air.
This has led to the production of 240, 000 tonnes of sulphuric acid, says Fitzpatrick. Acid dissolves aluminium, arsenic , zinc and lead, which could contaminate water supplies , he adds.
The discovery of sideronatrite will fuel fears that the acid will seep into the lakes, killing aquatic life.
Fitzpatrick says a proposal to flush out the acid with seawater would only be a short term fix, making the river even saltier than the sea. Two alternatives are being tested around lake Albert: spreading lime and growing acid resistant plants to neutralize the acid in the soil.
New Scientist (India ed.) 15th Dec.2008,vol.1,pp.15.