Underground pools of freshwater have been discovered about 10 m underground along Cooper Creek (pictured) in southwest Queensland, Australia, by a team from ANSTO, who say floods are essential to their existence.
SYDNEY: Researchers have discovered underground pools of freshwater in arid Australia that may be essential to the ecosystem and are maintained solely by floods, such as the ones that devastated Queensland in January.
The discovery will help scientists understand how plants, animals and farmers can survive in arid and semi-arid regions and may alter the way that floods are managed - and considered - in these areas.
“Most of the current water in that part of the world is quite salty, so the possibility of having some fresh, useful water is important for the farmers and the plants in the area. Flooding is essential to keeping it there,” said Dioni Cendón, a hydro-geologist from the Australian Nuclear Science and Technology Organisation (ANSTO), who led the research.
Rainfall is not the source
The freshwater, which floats on top of the denser salty groundwater because it is lighter, is known as ‘lenses’, and was discovered about 10 m underground along Cooper Creek in southwest Queensland, Australia, by the ANSTO team.
Although freshwater lenses had previously been suspected, as many plants survive during drought even some way back from waterholes and rivers, they had previously only been found around the Murray River and scientists didn’t know much about how they were formed.
“This is the first study that analyses them in more depth. In this part of the world, rainfall is really scarce – about 125 mm per annum – and we’ve found that all the recharge of these groundwater lenses is from the Australian summer monsoon,” said Cendón.
Flood dependent lenses
The team, which included researchers from the University of Wollongong, the University of Southern Queensland and the University of Barcelona, discovered the lenses by accident while studying nearby sand dunes.
They analysed the freshwater using water stable isotopes, which tell scientists what type of water feeds the groundwater, and also its salinity.
They found that there is little exchange between the waterholes and the groundwater, except for during floods, and that the freshwater – which can stretch up to 1 km away from the waterholes – becomes saltier the further it travels.
“Three hundred metres from the billabong the water is really fresh and you could drink it, but as you go further away it gets saltier and saltier,” said Cendón.
