Restoring desert crusts may control dust pollution better than spraying water
On a blustery March morning, a wind gust lifted a dust wall hundreds of feet high from a bare piece of land south of Coolidge. It engulfed 23 cars and was blamed for a road accident. Ten days later, it happened again, a dust cloud, a car accident.
The source of the hazard was an unplanted plot of fine-grain soil that ran for half a mile along State Route 87. That day, a machine operator was preparing to level 160 acres for the planting season when the dirt was swept by gusts of wind. Accident victims sued the farmer and won a $400,000 settlement.
In the roughly 20 years since the accidents, seasonal dust storms and serious concerns over fallow fields have persisted. Dust storms remain the second-biggest cause of road accidents in Arizona, and thousands of people fall sick every year from wind-transmitted, deadly fungal infections. The increased number of dry, unplanted plots in Pinal County due to recent water cuts could worsen the problem.
Some researchers believe they are close to new solutions. A team from Arizona State University is testing ways to grow back the “skin” of desert soils — the thin, living, natural layer that prevents wind from scooping up dust.
By monitoring dust sources and unique weather events and evaluating two bio-inspired methods to grow new soil crust, the team aims to offer new solutions for immediate and long-term dust control.
The methods are not entirely new. Biological crust restoration and enzyme-induced carbonate precipitation have been studied for over a decade. But applied research at this scale is still rare for biocrust, and until now there has been no commercial application of either method for dust control.
“The best available technology for fugitive dust control, like a construction site, is to run a water truck. And in Arizona, when it's 40 degrees centigrade and it's 15% relative humidity, you can run a water truck all day,” said Edward Kavazanjian, a researcher on the grant and the director of the Center for Bio-mediated and Bio-inspired Geotechnics.
“We wanted to find a better way, a more sustainable way ”
The research project is funded by a three-year $4.5 million grant from the Arizona Board of Regents, which will also support research at Northern Arizona University and the University of Arizona, where scientists study the growth patterns and transmission of coccidioides fungal spores, and are working to track hotspots of the fungus.
Polluted air: Summer storms are a spectacle, but the dust in them is hazardous to your health
Building new desert skin
On January 25, Pinal County said that new, more stringent dust-control rules will take effect in June on the western side of the county, arising from Environmental Protection Agency guidelines.
In 2012, the EPA determined that the area does not meet national air-quality standards for PM-10, air-suspended particles of dust and smoke 10 micrometers or less in diameter. That placed the west Pinal area as a PM-10 “non-attainment” area. In 2020, the EPA reclassified it as “serious non-attainment.”
Arizona failed to meet the deadline to achieve attainment and will now have to prove that west Pinal County is reducing its PM-10 emissions by 5% every year.
The situation is identical to what Maricopa County experienced some years back. If west Pinal County doesn't achieve the 5% reduction, the government could freeze federal transportation funds, and new projects could be put on hold until a new dust-control plan is submitted and approved by the EPA.
The penalty would be a massive punitive action, according to Timothy Franquist, environmental director of the Maricopa Association of Governments, the agency leading the effort to create a new state plan for west Pinal County. The situation in Pinal County is different than the one in Maricopa mainly because of the scale of the issue.
“It is a low-risk situation because we have identified control measures,” said Franquist.
The measures can be very expensive. The most important will likely be paving dirt roads, which make up 67% of all PM-10 emissions according to the most recent inventory from 2017. Other steps include watering, an expensive measure in the desert, and treating both construction sites and miles of roads with dust suppressants.
Synthetic polymers and a wide array of other products are frequently used for dust control on roads and construction sites. Annual treatment costs about $10,000 per mile. But some of them may be toxic and are not as suitable for large areas of ground, like fallow fields.
A more sustainable solution to keep dust in the ground, according to ASU researchers, would be to build new soil crust for immediate and long-term relief.
Biocrust restoration recovers and accelerates the growth of microbial communities that are naturally present in desert soils, and creates a living layer that protects soil from wind erosion. Enzyme-induced carbonate precipitation, or EICP, is a bio-inspired technique that uses bean-extracted enzymes to precipitate calcium carbonate in the soil (a main component of limestone that is regularly used in agriculture) and creates an artificial crust.
The idea is that biocrust restoration could be used as a long-term solution for plots that might be left fallow indefinitely, while the calcium carbonate crust could act as a treatment for areas that require immediate dust suppression.
Matthew Fraser and Pierre Herckes, also from the ASU team, will continue to monitor wind-blown dust with 14 sensors placed throughout the area, identify extreme weather events and agricultural activity and trace the source of dust to measure the treatments’ effectiveness.
Repairing the land: How researchers hope to preserve and restore 'biocrust,' the desert's protective skin
Biocrust research is growing
Biocrust restoration research has exploded in the last decade, and land managers are increasingly more invested in protecting biocrust as a key resource, said U.S. Geological Survey ecologist Sasha Reed, who has worked extensively in arid lands restoration but is not part of the ASU research team.
For fallow plots that will go unplanted indefinitely, this could be a long-term solution. The mighty microbes are “ecosystem engineers” that can improve habitat for other species and endure extreme weather events but would die crushed under tractor tires.
“It is a self-perpetuating ecosystem. It's the natural way the desert has to keep the soil in place,” said Ferran Garcia-Pichel, a biological soil crust scientist and researcher on the regents' grant.
Biocrust restoration at this scale has never been done. ASU's one-acre plot experiment is one of the largest scales attempted. A larger restoration project was attempted in Utah and was “the world's largest and maybe the world's only biocrust farm outdoors,” according to Reed with the USGS, who took part in the project. The biocrust died when it was taken from the breeding grounds into the field.
The ASU team faces similar hurdles. Out in the open, biocrust is not growing as fast as they need. In natural conditions, it can take decades for it to repopulate an area.
“And of course, that's not quick enough,” said Brian Scott, a scholar conducting ASU's field trials in Pinal County. “We need to be able to grow biocrust in our incubation chambers in a season and get it transplanted into the field.”
Reed, with the USGS, believes this is precisely the scale at which science needs to be happening today. There is a wealth of research and management experience to support biocrust restoration, and it will be needed so more tools for arid lands restoration in the West are available soon.
“We need to know these things now so that managers have options,” she said.
Dry lands: ADEQ is treating soil along I-10 in Pinal County to reduce dust storm risk
Agricultural dust control is one small piece of the puzzle
The quest to reduce PM-10 emissions by 5% each year in west Pinal County will require a holistic approach. New rules for construction sites will be in place in June, and cities in the county will have to scale up road paving starting next year.
Farmers will also be expected to adopt more best management practices, such as leaving crop residue on the fields for longer, establishing multi-year crops or planting wind barriers.
Agricultural plots are not the major source of dust in west Pinal County. According to a 2017 inventory of PM-10 sources, 67% of all dust came from 5,897 miles of unpaved roads. A wide variety of users stir dust from them daily. Harvesting and tilling practices made up only one-tenth of total daily dust levels.
But land tillage, laser land-leveling and harvesting can still create significant road visibility issues and health hazards.
Since 2006, the Arizona Department of Environmental Quality, which oversees agricultural best management practices, has received 81 complaints about dust coming from farms.
“Farm machinery is kicking up dirt making a giant cloud covering the whole neighborhood in the skyline ranch subdivision and further,” wrote one complainant in 2019. “I suffer from asthma and this is a serious health hazard for the children walking to schools in the area. This has been going on for YEARS.”
The agency has conducted 132 inspections since the non-attainment area was declared in 2012.
Another source of dispute is how much the extreme weather exacerbates the dust problem. Paul Ollerton, the farmer sued for the dust-cloud wreck about 20 years ago, is now chairman of a committee within ADEQ that oversees dust-control methods for farming.
In his view, most farmers abide by best practices and do what they can to avoid dust, tilling only when necessary and running a water truck when they level the ground. He said the EPA should analyze more closely the influence of high winds and the region's soil types.
At the time the road accident occurred, an operator in Ollerton’s farm was running a water truck to settle the dust during leveling, he said.
“It was out of my control. We did everything to the best of our financial ability and knowledge to prevent it," he said. “You just can’t put enough water out.”
When Maricopa County was fighting for PM-10 attainment, officials argued that much of the dust-levels issue was out of their control, classifying as “exceptional events” the driving cause of air pollution. The EPA agreed.
Ollerton has been outspoken and pushed back against some of the demands of the EPA that farmers adopt more best management practices. He also delivered more information and records of their activity to the agency.
The increase in fallow land is something to worry about, he said, and farmers will need support in finding new, better ways to deal with dust on their plots.
“A lot of our (best management practices) are based on, you know, using water, using water, using water, he said. "And water, it's just not there anymore."
Clara Migoya covers environment issues for The Arizona Republic and azcentral. Send tips or questions to firstname.lastname@example.org.
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This article originally appeared on Arizona Republic: Fallow fields worsen dust hazards, ASU tests bio-inspired solutions