Dropping Water Levels and Rising Salinity Push Great Salt Lake to Brink of
Ecosystem Collapse
Denver, Colo., USA: Great Salt Lake is well known for being salty, but
record-low water levels driven by high water usage and several years of
drought may soon make it too salty for even the brine shrimp that have made
it a home. The lake provides an important source of food for migrating
birds and supports a multi-million-dollar brine shrimp industry, both of
which could be lost if water levels don’t rebound soon. Carie Frantz of
Weber State University has spent the last several summers studying the lake
with teams of undergraduate researchers, checking on the health of
microbialite reefs that form the bedrock of the lake’s ecosystem. Frantz
will share their findings at the GSA Connects meeting in Denver this
Sunday, 9 October.
Great Salt Lake’s microbialites are rocky mounds built by mats of microbes
that create carbonate minerals—the same basic constituent of limestone.
Microbes in the reef, like algae and cyanobacteria, perform
photosynthesis—providing the nutritional basis for the rest of the lake’s
ecosystem. Brine flies lay their eggs on the reefs, and both the brine
shrimp and brine flies—two of the biggest populations at the lake—feed from
the reefs. Because the lake is too salty for fish, there are few predators,
so the lake can become dense with the flies and shrimp, which then feed a
large population of both migrating and resident birds. As lake levels have
dropped, previously underwater reefs have become exposed to the air,
causing the aquatic microbial communities to die off. As the microbes die,
the reefs become bleached—changing color from dark green to white.
In 2021, Frantz and her students found evidence that the microbialite reefs
might be resilient to the negative impacts of low water levels and be able
to recover from bleaching, but the same experiments in 2022 cast doubt on
that hopeful outlook. Students experimented with re-submerging bleached
microbialite pieces into the lake by putting them in mesh bags attached to
an underwater pipe. Even microbialites that looked dead still contained
living microbes that recolonized the microbialite pieces when they were
submerged back into the water—and this recovery was quick, with exponential
growth of microbes, hinting that full recovery might be possible within several months. When they repeated the experiment in 2022, however, they did not see the
same quick recovery.
Frantz attributes this change from 2021 to 2022 to increased salinity. As
the water level keeps dropping, the lake keeps getting saltier. In 2021,
she saw salinity levels as high as 18%, already above what is considered
healthy for the Great Salt Lake ecosystem, which is typically 12–15%
salinity. In 2022, she saw those measurements climb above 19% in open water
areas and reach as high as 26% within the reef she and her students monitor
(for reference, the ocean has a salinity of ~3.2%; salt precipitates from
Great Salt Lake water at a salinity of ~27%).
Frantz explains, “Last year, it was really encouraging, because we saw that
they can come back, and they come back fast. This year we saw something
very different, we don’t see that clear increase we saw last year. The
organisms are stressed at these salinity levels. It’s possible it’s just
too high for them to grow.”
In the 1950s, the Great Salt Lake was split into northern and southern
halves by the building of a railroad causeway. Because most of the fresh
water coming into the lake goes to the southern portion, the north section
experienced a mass die-off of photosynthetic microbes that can be observed
from space—emanating a pink hue produced by the few salt-loving microbes
that can survive its hypersaline water, which exceeds 25% salinity. The
southern half of the lake may suffer the same fate if more water isn’t
brought into the system soon. Frantz estimates that without major
interventions, it could be a matter of months to a few more years before
the ecosystem collapses. Scientists monitoring brine shrimp and brine flies
in open water areas of the lake have already begun to report worrisome
trends in the behavior of brine shrimp, brine fly larvae, and the birds
that rely on them.
Some legislative measures have been taken in the past year to attempt to
secure water rights for Great Salt Lake, but Frantz worries it won’t be
enough to prevent a collapse, saying “It’s a slow shift in response to an
emergency—we’re not acting as fast as the situation calls for.”
Documenting a Geobiological Tragedy: The Exposure of Great Salt Lake's
Microbialites and the Undergraduate Researchers at the Vanguard
Author contact: Carrie Frantz, Weber State University, cariefrantz@weber.edu
Sunday, 9 October 2022, 3:35–3:50 PM
https://gsa.confex.com/gsa/2022AM/meetingapp.cgi/Paper/383654
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