April 25, 2017
Human activity risks contaminating pristine water stockpiled
deep underground since the age of the mammoths, said a study Tuesday that warns
of a looming threat to a critical life source.
Generally stored at depths of more than 250 metres (820
feet) under the Earth's surface, the ancient resource had been assumed to be
shielded from pollution by humans—who rely on it more and more as shallower
sources dry up.
Now, researchers have found traces of modern-era rainwater
in wells that bring "fossil" groundwater to the surface—pointing to a
contamination risk.
"It's a bit like going to an old folks' home and
suddenly realising there are also little kids running around. That's great,
except if the little kids have the flu," said study co-author James
Kirchner of the Swiss Federal Institute of Technology in Zurich.
The fear, he explained, is that younger water may pollute
the ancient aquifers with fertilisers, pesticides or industrial runoff from
Earth's surface—though they have not found any evidence for this yet.
Groundwater is rain or melted ice that filters through
Earth's rocky layers to pool in aquifers—a process that can take thousands,
even millions, of years.
It is the largest store of unfrozen fresh water on Earth.
Groundwater is pumped to the surface with wells for drinking
and irrigation, and supplies about a third of human water needs.
Thinking long-term
For the latest study, presented at a European Geosciences
Union meeting in Vienna, a research team set out to determine how old Earth's
groundwater really is.
They used radiocarbon and tritium content to distinguish old
from young groundwater and determine their relative abundance.
Radiocarbon, on the other hand, takes almost 6,000 years to
decay. It is therefore much less abundant in fossil water.
The data showed that "most of the groundwater under our
feet is surprisingly old," said Kirchner.
Roughly half—potentially more—dates from 12,000 years ago or
more.
"The assumption would be if your groundwater comes from
a time when mammoths were roaming the Earth, that those mammoths did not have
chlorinated hydrocarbons," Kirchner explained.
"If your water dates from a... pre-industrial era, the
assumption would be it can't be carrying industrial-era contaminants down
underground."
Against expectations, however, the team found that about half
of "fossil" groundwater wells they studied contained detectable
levels of tritium, indicating the presence of younger water.
"This observation questions the common perception that
fossil groundwaters are largely immune to modern contamination," concluded
the study, published in the journal Nature Geoscience.
Fellow author Scott Jasechko, of the University of Calgary,
said the findings were worrying on two levels.
Not only may "fossil" groundwater be exposed to
contamination, it would also take millennia to replenish once used up.
"Conserving groundwater for future generations is
important and requires us to consider timespans beyond the typical political or
land management timescales of years or decades," he told AFP.
The High Plains aquifer in the United States, for example,
would take an estimated 6,000 years to refill, according to the study authors.
And Libya's Nubian aquifer, formed in a geological epoch
when the now-dry region was wet and green, is being depleted at a rate of six
million cubic metres of water per day."
Dag Dick,
De geohydrologen bij de
waterbedrijven weten dit volgens mij.
Ook Vitens heeft een meetmethode
waarbij ze de ouderdom van hun water kunnen meten. Ook dat blijkt soms 10.000
jaar oud. Nu is Nederland erg nat en komt er per jaar 10 keer meer water
binnen, dan we met z’n allen gebruiken. Maar “het opmaken” gaat natuurlijk veel
sneller, dan die ondergrondse aquifers weer gevuld kunnen worden.
Het risico is groot dat steeds meer
“primary water” toch aangeboord zal worden voor de landbouw, de frisdrankenindustrie
en de waterbedrijven. Inderdaad een grote zorg.
Met vriendelijke groet,
F.S.
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