The world’s tallest sand dunes, some half a kilometre high, survive in a windy desert in northern China because water cements them together, a new study suggests. The researchers that made the discovery in the Badain Jaran desert suspect the water seeps up from a vast underground reservoir which is replenished by snow melting on distant mountains. “Our finding could transform plans for the region’s water resources,” says the team, led by Jian Sheng Chen of Hohai University in Nanjing, China. Up to 500 billion litres of water could be extracted from the desert every year, the scientists suggest.“The idea that water stabilises the sand dunes is interesting,” says Mike Edmunds, research director of the Oxford Centre for Water Research in Oxford, UK, but he takes issue with the suggestion that the underground water could be extracted to meet local demand. “They are trying to recommend this as a new water resource when in fact it’s fossil water. It is from a past climate,” Edmunds told New Scientist. He has collected data in the same desert and says there is no evidence that the water levels are being topped up by melting snow. The Badain Jaran desert has a unique landscape of towering sandy dunes and shallow lakes. Chen and colleagues dug into one of these dunes and were surprised to discover moisture just 20 centimetres below the surface, despite the fact that they were high above the level of the lakes. “The water found is clearly essential for maintaining the stationary dunes,” says Ling Li, a member of the team. In other windy deserts, dunes tend to migrate in the direction the wind blows. The team measured the concentration of different elements in dune- and lake-water to collect clues about where it came from. They say the ratio of different oxygen isotopes, for example, matches the profile of snow on the Qilian Mountain, 500 kilometres to the southwest. And that dissolved strontium shows the melt-water flooded through deep subterranean faults to reach the desert. From looking at other elements they deduced that the water had taken 20 to 30 years to make the journey.But Edmunds considers this conclusion to be flawed. “They’ve taken two and two and made 73,” he says.
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