The science behind the life and times of the Earth's salt flats

Date:
May 1, 2023
Source:
University of Massachusetts Amherst
Summary:
Researchers have characterized two different types of surface
water in the hyperarid salars -- or salt flats -- that contain
much of the world's lithium deposits. This new characterization
represents a leap forward in understanding how water moves through
such basins, and will be key to minimizing the environmental impact
on such sensitive, critical habitats.


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FULL STORY ========================================================================== Researchers at the University of Massachusetts Amherst and the University
of Alaska Anchorage are the first to characterize two different types of surface water in the hyperarid salars -- or salt flats -- that contain
much of the world's lithium deposits. This new characterization represents
a leap forward in understanding how water moves through such basins,
and will be key to minimizing the environmental impact on such sensitive, critical habitats.

"You can't protect the salars if you don't first understand how they
work," says Sarah McKnight, lead author of the research that appeared
recently inWater Resources Research. She completed this work as part of
her Ph.D in geosciences at UMass Amherst.

Think of a salar as a giant, shallow depression into which water is
constantly flowing, both through surface runoff but also through the much slower flow of subsurface waters. In this depression, there's no outlet
for the water, and because the bowl is in an extremely arid region,
the rate of evaporation is such that enormous salt flats have developed
over millennia. There are different kinds of water in this depression; generally the nearer the lip of the bowl, the fresher the water. Down
near the bottom of the depression, where the salt flats occur, the water
is incredibly salty. However, the salt flats are occasionally pocketed
with pools of brackish water. Many different kinds of valuable metals
can be found in the salt flats -- including lithium -- while the pools
of brackish water are critical habitat for animals like flamingoes
and vicun~as.

One of the challenges of studying these systems is that many salars
are relatively inaccessible. The one McKnight studies, the Salar
de Atacama in Chile, is sandwiched between the Andes and the Atacama
Desert. Furthermore, the hydrogeology is incredibly complex: water comes
into the system from Andean runoff, as well as via the subsurface aquifer,
but the process governing how exactly snow and groundwater eventually
turn into salt flat is difficult to pin down.

Add to this the increased mining pressure in the area and the poorly
understood effects it may have on water quality, as well as the
mega-storms whose intensity and precipitation has increased markedly
due to climate change, and you get a system whose workings are difficult
to understand.

However, combining observations of surface and groundwater with data
from the Sentinel-2 satellite and powerful computer modeling, McKnight
and her colleagues were able to see something that has so far remained invisible to other researchers.

It turns out that not all water in the salar is the same. What McKnight
and her colleagues call "terminal pools" are brackish ponds of water
located in what is called the "transition zone," or the part of the
salar where the water is increasingly briny but has not yet reached
full concentration. Then there are the "transitional pools," which are
located right at the boundary between the briny waters and the salt
flats. Water comes into each of these pools from different sources --
some of them quite far away from the pools they feed - - and exits the
pools via different pathways.

"It's important to define these two different types of surface waters,"
says McKnight, "because they behave very differently. After a major
storm event, the terminal pools flood quickly, and then quickly recede
back to their pre-flood levels. But the transitional pools take a very
long time -- from a few months to almost a year -- to recede back to
their normal level after a major storm." All of this has implications
for how these particular ecosystems are managed.

"We need to treat terminal and transitional pools differently," says
McKnight, "which means paying more attention to where the water in the
pools comes from and how long it takes to get there." Parts of this
research were funded by the Albemarle Corporation.

* RELATED_TOPICS
o Earth_&_Climate
# Water # Drought_Research # Ecosystems # Floods #
Environmental_Issues # Pollution # Recycling_and_Waste
# Sustainability
* RELATED_TERMS
o Sea_water o Environmental_impact_assessment o Water_resources
o Ocean_surface_wave o Evaporation_from_plants o
Underwater_explosion o Desalination o Ecotourism

========================================================================== Story Source: Materials provided by
University_of_Massachusetts_Amherst. Note: Content may be edited for
style and length.


========================================================================== Journal Reference:
1. S. V. McKnight, D. F. Boutt, L. A. Munk, B. Moran. Distinct
Hydrologic
Pathways Regulate Perennial Surface Water Dynamics in a Hyperarid
Basin.

Water Resources Research, 2023; 59 (4) DOI: 10.1029/2022WR034046 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/05/230501163955.htm

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