A life in the desert is a life of extremes; sweltering heat, thunderous downpours and dust storms that bring traffic to a standstill.
Seeking shelter, staying hydrated and applying ample sunscreen are manageable rituals for the Sonoran Desert dweller, but what happens when the air is no longer safe to breathe because of soil erosion so severe that dust has filled the skies?
This is a scenario Arizona soil scientists are working hard to avoid through innovative restoration projects happening across the state.
Healthy desert soils are teeming with life. Dense aggregates of microscopic organisms including mosses, lichens, cyanobacteria (also known as “blue-green algae”) and other types of algae occupy the uppermost few millimeters of soil, knitting it together to form a protective layer known as “biocrust” that prevents erosion and dust storms.
These organisms work together to stabilize the earth below by using enzyme secretions that act as a glue. To the untrained eye, biocrusts are difficult to spot. This is particularly true in deserts where there isn’t much greenery.
However, experts like Arizona State University professor and soil researcher, Dr. Ferran Garcia-Pichel, know exactly what to look for.
“In the desert, the crust turns black because the organisms have sunscreens all over themselves,” explained Garcia-Pichel. They’re remarkably hardy and able to exist in a dormant state during periods of low rainfall.”
This is what he and his team look for during the dry season when they’re extracting samples to take back to the lab, however, biocrusts can look quite different after a summer monsoon.
Garcia-Pichel explained that following rainfall, microbes that usually lie just beneath the surface move up through the soil profile to dazzle spectators.
“You’ll see that it’s just all green,” he said.
This is also a good opportunity to see which areas no longer have a healthy biocrust covering. A lack of green suggests an absence of these organisms.
“It’s really eye-opening because you know, after it rains, which areas are impacted,” Garcia-Pichel said.
Urban expansion into the desert is the greatest threat to biocrusts. Sprawling suburbs, military activity, cattle grazing, other types of agriculture and uncontained recreational activities threaten soil health across Arizona.
“People driving four-wheelers off-road is a problem,” said Dr. Joey Blankinship, a University of Arizona professor and microbial biogeochemist.
Blankinship, who studies dust prediction in southern Arizona, is interested in understanding how recycled organic materials like manure and biochar (charcoal) can be used to improve agricultural productivity.
“Getting more carbon into the ground is good for climate change mitigation,” Blankinship said, commenting on one of the greatest threats to the desert.
He went on to describe the importance of also being economical so that there’s an incentive for those across the state to invest in restoration projects.
“We need to think about cheap ways of doing things from the beginning,” Blankinship said.
Polyacrylamide glues are often used as a substitute for the enzymes naturally secreted by biocrusts, but so far, these don’t seem to be a viable solution for depleted soils.
“These are routinely sprayed on the land, but we have data showing that they don’t work,” Blankinship explained.
While it’s clear that restoration of biocrusts is key in preventing erosion, it’s easier said than done; particularly with the rates of decline seen in southern Arizona.
“There’s not much left,” said Garcia-Pichel. “If you compare to somewhere that doesn’t have much of a human population, like southern Utah, it’s almost sad.”
In his laboratory at Arizona State University, Garcia-Pichel and his team are interested in using a nursery model to restore biocrusts in the desert.
The first step in the process involves going out to sites with healthy soils and extracting crust. Then, after a “CSI-type DNA analysis,” they know which organisms are present and thus able to grow in those specific environmental conditions. The scientists then isolate these species and keep them supported in the lab with all the nutrients they need to survive.
“At this point, we have like 200 different cultures,” Garcia-Pichel said, going on to explain that where restoration is required, one of these will be a good match.
As well as growing individual cultures, his team grows whole communities of organisms in a greenhouse setting, experimenting with sunlight and water levels to see what achieves optimal growth.
“We take a little crust, crush it, spread it over virgin soil and then grow it,” Garcia-Pichel explained.
The question at this stage is how to make the process scalable.
Although established biocrusts can do remarkably well in the Arizona summer heat, it turns out that fresh crusts require some amount of shade. The shade is particularly important as it slows the rate at which moisture evaporates from the ground following rainfall. Biocrusts can only grow when it’s wet, so some amount of shade during restoration initiatives is key.
“That’s when we started working with a solar farm,” Garcia-Pichel said.
Instead of using a 30,000 square-foot greenhouse, his team could experiment with shade provided across 500,000 acres covered with solar panels.
“We have a pilot experiment that started in Mesa last spring, collaborating with one of the solar companies,” Garcia-Pichel explained.
Unfortunately, last year was one of the warmest, driest years on record and less than ideal timing for the restoration study, but he’s hopeful that this year will reveal promising results.
“It’s looking better. After the recent rains we sampled and measured and it has recovered quite a bit,” Garcia-Pichel said.
One of Garcia-Pichel’s graduate students, Corey Nelson, who, up until recently, was leading this project discussed the importance of regular rainfall.
“It seems that the amount of rain is as important as how often it rains,” Nelson said.
It takes some time for biocrust organisms to rehydrate after a period of drought. If there isn’t enough rain, the organisms aren’t able to do much.
“They go back to sleep without gaining any energy or fixing any carbon,” Nelson explained.
Nelson’s research focuses how biocrusts form in the very early stages of colonization thanks to the cyanobacteria, Microcoleus spp. These organisms cluster together to form rope-like structures that help bind the soil together and encourage other organisms to move in.
“It’s a team effort,” Nelson explained, when discussing early biocrust formation, “like cyanobacteria and friends.”
Cyanobacteria seem to be the first of the biocrust-forming organisms in all types of environments, from arid deserts to woodlands. It’s simply a matter of which organisms take over as the crust matures.
A team at Northern Arizona University led by Dr. Matthew Bowker, a professor in the School of Forestry and biocrust researcher, are exploring restoration in a variety of ecosystems including the Sonoran Desert.
Taking a greenhouse approach where his team will grow biocrusts artificially before introducing them into the environment in varied quantities, Bowker is hoping to experiment with how much of the crust is needed to restore affected areas including the borderlands which have been heavily disturbed with Border Patrol traffic and border wall construction.
He is also interested in restoration near archaeological sites to see if this can prevent erosion, as well as how biocrusts behave in areas that have been recently burned.
“We want to see what amount of addition gives us the most bang for the buck,” Bowker said.
He went on to explain the importance of exploring ways to help the biocrusts adhere to the soil and withstand the elements.
Combining the biocrusts with a plant-derived soil stabilizer, psyllium husk, might improve success rates, but the amount required is still to be determined.
“We want to do a gradient of stabilizer with a gradient of crust additions and hopefully learn something about ideal recipes,” Bowker said.
One of the biggest issues that projects like this face, however, is that artificial biocrusts often don’t have the same stress tolerance as those in nature. This means that many of them don’t survive when they’re transplanted into the wild.
It’s unclear why this is the case, but Bowker suggested it could be, in part, because crusts in a greenhouse environment aren’t having to struggle for resources.
“We give them water, nutrients and everything they want, so they grow really fast,” Bowker said.
This could be making them less hardy and thus less able to cope with wind, heat and drought.
Bowker also emphasized the need for innovative ways of helping biocrusts adhere to the soil.
“We’ve been experimenting with biodegradable materials, like burlap cloth,” Bowker said.
The idea is that the team fuse the biocrust to a burlap cloth in the lab and then attach the cloth to the soil outside with the hope that the cloth acts as a protective barrier against the elements.
This has been achieved successfully in Montana grasslands using a mossy biocrust attached to a burlap cloth face down on the soil surface. Another one of Bowker’s students is now experimenting with new techniques and materials and Bowker said that one day something similar could be used in the desert too.
“For the desert environment, we might want to have a material that’s a little less long-lived than, say, burlap,” Bowker said, commenting on the need for the infrastructure to be biodegradable.
Another method that may be better suited to the desert is packing biocrusts into clay pellets that are distributed over the soil and allowed to degrade naturally.
“When the clay falls apart, hopefully it will help to attach the biocrusts inside to the soil surface,” Bowker explained.
He described the endless possibilities of experimenting with what else could be included in the pellet that may improve the chances of the biocrusts taking root.
“We might put in materials that prevent insects like ants from stealing the biocrusts, or various kinds of materials, such as water, that help bind them to the dirt,” Bowker said.
It’s a technology borrowed from the seed industry that has been used successfully, but for now, it’s a case of trial and error to optimize this technique for a desert environment.
As well as interest from the solar industry, which loses efficiency when panels are covered in dust, there appears to be a growing interest in biocrust restoration to boost vegetation in the Southwest, as well as minimize the impact that dust has on transport across Arizona.
“There’s definitely a growing interest,” Garcia-Pichel said.
Not even state-of-the-art technologies are immune to the effects of dust. On how solar farms are currently tackling the debris, Garcia-Pichel said, “they have to pay crews with squeegees!”
This highlights the need for collaborative efforts to minimize soil erosion across the state.
Agricultural land is another place where biocrust restoration can be beneficial. Biocrusts can add nitrogen to perennial crops without the need for fertilizer. Not much is able to be done on land used for livestock grazing. Rather, reducing the amount of land used for these practices is essential.
“I think we could do a better job of taking into account not only some of the benefits of livestock production, but also some of the environmental costs,” Bowker said. Dust, of course, being one of these costs.
The goal is to confine grazing to the most economically viable areas that aren’t as susceptible to erosion.
“It’s a direct health hazard. Vehicle accidents, respiratory problems and it’d be way better if we kept the soil on the ground where it belongs,” Bowker said.
While climate change continues to threaten ecosystems like the Sonoran Desert, initiatives like these help to ensure long-term viability for humans.
On whether the Sonoran Desert will eventually be uninhabitable, Blankinship said, “I’m not worried. I think it’s narcissistic of us [to suggest that] because they’ve survived worse.”
It’s more a question of how humans will learn to adapt.
“We need more local food production and wiser personal decisions among farmers,” Blankinship explained, going on to mention that low water-use crops must be the priority.
Whether fixed to a cloth sheet or housed within a clay pellet, there may come a time in the not-too-distant future when those living in the desert or elsewhere can purchase their own biocrust starter kits for backyard restoration projects. In the meantime, however, the message is clear: tread lightly on the earth.