Lake Formation and Expansion Due to Sea-Level Rise Causes Freshwater
Resource Depletion on Small Islands
Portland, Ore., USA: Coastal regions and small ocean islands face
significant risks from rising sea levels due to climate change, because
waters can flood and inundate low-lying land surfaces. “Climate change has
become a more critical issue recently, especially for island countries and
island provinces like the Bahamas. They are not only facing a water
shortage problem because of the limitations of the islands, but also they
are facing a coastal inundation problem due to sea level rise caused by
climate change,” said Yipeng Zhang, a postdoctoral associate at the
University of Texas at El Paso.
Zhang will
present research
on Wednesday at the Geological Society of America’s Connects 2021 annual
meeting in Portland, Oregon, that evaluates the impact on freshwater
resources on small tropical islands due to sea level rise.
“What makes the news quite a bit, rightfully so, when we think about
sea-level rise and islands is inundation and loss of land, especially for
low-lying islands, but our focus is water resources,” said Alex Mayer, a
professor of civil engineering at the University of Texas at El Paso and
principal investigator of this freshwater resource project. “In island
aquifers, freshwater is usually found on a lens sitting on top of seawater,
due to density differences. That [freshwater] lens can be a very precious
and valuable resource especially because many of these islands don’t have
access to sufficient surface water resources, so they’re maybe completely
dependent on the groundwater.”
While it has been well known that freshwater lenses shorten as sea level
rises and the coastline becomes inundated, thus putting freshwater
resources at risk, Zhang and Mayer’s research group focuses on the effects
of lakes forming and expanding on small islands. As sea level rises, there
will be more flooding or inundation in the center interior of islands, so
lakes or wetlands will expand laterally, and lakes may even form where
there were none previously.
“The lakes are in hydrologic connection to the groundwater. Evaporation
rates from the lake are much greater than the evaporation rates from the
land surface, and so the lakes can act as a pump, essentially, in drawing
water from below. And that can result in saltwater coming up all the way to
the surface,” said Mayer.
This “pumping” effect that brings saltwater to the surface can divide and
compromise the lens of freshwater, thereby reducing the volume of available
freshwater to use for drinking and other needs. To investigate the impact
of expanding lakes on freshwater resources, Zhang and Mayer modeled
different scenarios using a 30-year climate record from San Salvador Island
in the Bahamas and different rates of sea-level rise with seasonal climate
variability.
Zhang’s work in particular focuses on the effect of mixing at the interface
of the freshwater lens and saltwater below, because mixing between these
layers can contaminate the freshwater. As sea level rises and lakes form
and expand, the mixing zone increases, consequently reducing the available
freshwater. Seasonal climate variations between wet and dry phases also
cause enhanced mixing, since the lens will grow in the wet season and
retract in the dry season, thus moving back and forth in a cyclical motion.
Understanding the impact of sea-level rise and lake formation on freshwater
lens resources is critical in developing sustainable groundwater management
strategies for ocean islands. For islands that rely on this groundwater as
their main source of potable water, desalination may become an inevitable
part of their future.
“I would hope there’s some kind of climate justice involved, too, to help
island nations overcome the problems of sea-level rise,” said Mayer. “In my
mind, the island nations did not cause the problem, it’s the responsibility
of the industrialized nations.”
This research is in collaboration with scientists at the University of
South Florida and the University of Florida, with funding from the
National Science Foundation.
Session 230: D12. Coastal and Marine Hydrology in an Age of Rising Seas:
From the Margin to the Oceanic Ridge
Paper 230-3:
Freshwater resource depletion on ocean islands as lakes form and expand
with sea level rise
Wednesday, 13 Oct., 2:05–2:20 p.m., Oregon Convention Center room D137
https://gsa.confex.com/gsa/2021AM/meetingapp.cgi/Paper/370157
Contacts:
Yipeng Zhang, The University of Texas at El Paso, yzhang12@utep.edu; Alex
Mayer, The University of Texas at El Paso, amayer2@utep.edu
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