“This global view of groundwater will, hopefully, raise awareness that our youngest groundwater resources – those that are the most sensitive to anthropogenic (man-made) and natural environmental changes – are finite”, said Ying Fan of Rutgers University, in an article for Nature Geoscience that complemented Gleeson’s study.
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An global team of hydrologists has come up with the best estimate yet for Earth’s total supply of groundwater, saying that almost 23 million cubic kilometres of groundwater is contained in hidden reserves under the surface of the planet.
A new study found that groundwater supplies in the upper layers of the Earth take very long to renew.
Of the total, just 0.35 million cubic kilometres is less than 50 years old.
Researchers will now be painting a full picture of how quickly is old and modern groundwater being depleted because of human activities and to analyze volumes of groundwater in relation to how much is being used and depleted.
They estimated that the total amount of groundwater in the world was 22.6 million cubic kilometres – enough to cover all the land on Earth to a depth of 180 metres.
Dr Gleeson said: ‘This has never been known before. We already know that water levels in lots of aquifers are dropping.
Gleeson: The simplest answer is because over a third of humans drink groundwater every day and we use it for irrigated agriculture around the world.
Why is it so important to differentiate between modern and old groundwater.
Key to determining the age of all this stored water is a collection of thousands of tritium measurements. It can contain arsenic or uranium and is often more salty than seawater, he added.
That small fraction is referred to as “modern” groundwater: it is extractable because it is near the surface, and can be used to supplement above-ground resources in rivers and lakes.
Although water found closer to the surface is being renewed quicker than the water found deeper in the Earth, it is more sensitive to contamination and climate change, but it can also serve to temper climate extremes, he said.
According to the paper, only six per cent of the world’s groundwater is replenished in 50 years’ time.
“Additionally, our results are more based on measured groundwater data such as tritium concentrations and water levels, and recent global maps of permeability and porosity”.
According to the study, most groundwater is found in tropical and mountainous regions, with a few of the largest deposits in the Amazon Basin, the Congo, Indonesia and along the western borders of North and South America. But these areas are mostly under permafrost and contain little groundwater.
Dr Kevin Befus, who was another of those involved in the study while at the University of Texas and now works at the US Geological Survey, said: ‘Intuitively, we expect drier areas to have less young groundwater and more humid areas to have more, but before this study, all we had was intuition.
‘Now, we have a quantitative estimate that we compared to geochemical observations’.
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Our groundwater studies are really important to show and to try to estimate how much groundwater we have and where we have it, and that can be used for how to better manage it. This is true across Canada. But groundwater development has also depressed water tables, degraded ecosystems and led to the deterioration of groundwater quality, as well as to conflict among water users.
