Upwind from northern Utah’s urban centers is a network of lakebeds, dried-up remnants of a vast prehistoric inland sea that dominated the region when the climate was much wetter and cooler that it is today.
Now, as western Utah becomes even drier — from drought, water diversions and climate change — these playas have become a major source of dust settling on Wasatch Front cities and their mountain water sources, according to new research conducted by Brigham Young University geologists.
Led by geology professor Greg Carling, the study concluded 90% of the dust is blown off the exposed beds of the shrinking Great Salt Lake, Sevier Lake and other valley bottoms once covered by ancient Lake Bonneville.
“Lakebeds are muddy, but as they dry out, they become a dustpan,” said study co-author Michael Goodman, a former BYU graduate student now working as an environmental consultant in Houston. “Dry lakebeds are becoming a significant dust threat to nearby communities, not only impacting air quality but also impacting soil and what can grow in it.”
Airborne dust is considered a form air pollution, known as large particulate matter, or PM10. It is not as dangerous as fine particulate PM2.5 because it is not easily absorbed into lung tissues. But it remains a serious problem, particularly on the four to five days a year when major winds turn the Wasatch Front’s airshed gritty and darken the snowpacks that store water for Utah’s thirsty cities.
Accordingly, lakebed dust has become the focus of intense scientific scrutiny in the past decade. Geographers and geological and atmospheric scientists with the University of Utah closely study the beds of the Sevier and Great Salt Lake, as well as dust accumulating on Wasatch snowpacks, in an effort to understand how land-use practices and water diversions affect water supplies and alpine environments.
It's an alarming picture.
Scientists like the U.'s McKenzie Skiles have proved that West Desert dust storms leave a dark coating on the Wasatch snowpack. By reducing the snow’s ability to reflect heat, the dust accelerates the spring runoff, ensuring less water is available for stream and human uses.
“It’s a symptom of our water-use policies,” said Kevin Perry, another U. atmospheric scientist who recently completed an comprehensive analysis of the Great Salt Lake’s exposed bed. “We are poor at conserving water, and we have some of the highest per capita use of water. This is one of the consequences of not being waterwise in a desert ecosystem.”
Although drought is a factor, water diversions are the main reason the Great Salt Lake is shrinking, leaving about 750 square miles of bed exposed, and Sevier Lake is a memory.
According to a 300-page report Perry submitted this fall to the Utah Department of Natural Resources, much of the Great Salt Lake’s bed is protected by a crust that keeps windstorms from spreading dust.
“Only 9% of the lake right now is blowing dust," Perry said. "If the crust were to erode or be destroyed, then a maximum of 22% of the lake would actually have enough silt and clay particles to become dust sources. We know where those sources are. We know what needs to be protected.”
BYU’s new study adds to this science by attempting to characterize the quantity and quality of the West Desert dust falling on Utah’s big cities and nearby water sources in the mountains.
The BYU team collected more than 100 samples at 15 locations in Utah’s West Desert, including the dry beds of the Great Salt Lake and Sevier Lake, Tule Valley, Wah Wah Valley, Sunstone Knoll, Fumarole Butte, Pismire Wash, Fish Springs and Dugway Proving Ground.
They also collected samples in four major northern Utah cities from Provo to Logan and on spring snowpacks in the Wasatch and Uinta mountains.
Dust from particular sources exhibited distinct ratios of various isotopes, providing a signature that could match samples collected in the cities with specific source sites, according to Goodman. This isotopic analysis revealed the dry Sevier playa is a major source of dust turning up on the Wasatch Front.
A secondary takeaway from the BYU study is that dust deposits containing harmful elements are more likely coming from the cities themselves or mining sites, according to Carling.
“Even though the urban and mining area contributes only a small fraction of the dust load," Carling said, “it contains the most contaminants, such as antimony and copper."
The study, published in the journal Chemical Geology, was funded by the National Science Foundation and the Utah Division of Forestry, Fire, and State Lands. Co-authors included BYU geology professors Barry Bickmore, Stephen Nelson and Kevin Rey, as well as former student Colin Hale. U. professor Diego Fernandez and Jeffrey Munroe of Middlebury College also assisted with the research.