Fighting Against a Global Dust Bowl

Development, drought, and other factors have conspired to turn wide stretches from grassland and farmland into dusty deserts and scrubland. But there are some ideas about how to fight that trend and prevent dust from poisoning people and contributing to global warming.

By Michael Tennesen|Friday, November 12, 2010
duststorm
duststorm
Image: iStockphoto

Greg Okin, a professor of geography at the University of California at Los Angeles, recalls being caught in a dust storm off Interstate 10 in the Coachella Valley some years ago. “You couldn’t see ahead of you, so you had to slow down. But when you did, you started thinking about what was behind you. What car was going to plow into you because it couldn’t see.”

What Okin experienced was just one gust in a gathering storm. Blowing dust and brownout conditions on January 19, 2009, created a chain reaction of fatal crashes on I-70 in eastern Colorado. In July a massive dust cloud descended on Iraq, forcing the police to wear masks while directing traffic through the strangely dark streets of Baghdad. In September one of Australia’s worst dust storms in 70 years clogged the skies over Sydney with 5 million tons of particles, causing international flights to be diverted and prompting a spike in emergency calls from people who were having trouble breathing. And such disruptions can take on a global dimension. Satellite images show storms in northern Africa blowing particles all the way to the Amazon Basin. Plumes from northern China can reach Hawaii and California. A 2002 dust storm from the Gobi Desert tracked east across the Pacific Ocean, past the United States, and out into the Atlantic.

The problem has been building for a long time. Wars, oil and gas exploration, agriculture, cattle production, and general development have broken up soil surfaces around the world. Drought, rising temperatures, and a shift in some regions from grasslands to shrublands have accelerated the problem in the past 10 to 15 years. In the United States, the loss of grasslands and other natural shields that hold arid soils in place is particularly pronounced in New Mexico, Arizona, and Nevada, where dust production has increased by orders of magnitude over the past several decades. And dust begets more dust: It reduces the reflectance of the winter snowpack and increases the absorption of sunlight, causing snow to melt sooner. Five times as much dust now falls on the snowpack in the Colorado Rockies as when the area was first heavily settled in the mid-19th century.

Hence dust is both symptom and cause of a grim type of environmental decline: desertification, the degradation of vital grasslands into barren and unproductive desert. This process unfolded with horrifying consequences in the 1930s, when large portions of the Great Plains states turned into the Dust Bowl as a result of lack of rain and poor farming practices. Millions of acres of fertile topsoil blew east, toward and into the Atlantic Ocean, devastating American agriculture.

Desertification is happening today around the world, most notably in northern China, home to much of that nation’s 1.2 billion citizens. “The world needs more food, more land to grow it, and more water to irrigate it, yet we have the same amount of land, less water, and higher temperatures,” Okin says. “This is a train wreck about to happen that will impact hundreds of millions of people now and perhaps billions in the future, because that’s how many live in dry lands worldwide.”

Last year was a record one for dust production in the United States, when sparse and badly timed desert rains produced the lowest vegetation cover on record and 5 to 20 times as much dust as usual from the Colorado Plateau into the mountains. The snowpack melted about 50 days early because dust put massive stress on high mountain vegetation and lowland farms and fields. In southern Colorado scientists reported the most rapid snowmelt since the mid-1980s, when records were first kept. “Increased runoff caused by dust on snowpack acts as a major leak in the reservoir system,” says Thomas Painter, a professor of geography at the University of Utah.

Okin thinks this may be just a hint of things to come. “Climate models predict that the Southwest should get warmer and drier,” he says. “By 2050 soil moisture could be lower than it was in the Dust Bowl era.”

Dust is two-faced—a lesson I am about to learn as my plane descends to the desert near Las Cruces, New Mexico, where I am to meet Okin and see his work. Dust can be beneficial to parts of the planet, as when it travels from the Sahara to the Amazon Basin, where it deposits phosphorus that helps keep the rain forest lush. Similarly, dust from northern China brings phosphorus and other vital nutrients to the Hawaiian Islands. Dust from the many continents ferries iron and phosphorus to the ocean surface, promoting the growth of phytoplankton and other marine plants that feed sea organisms and draw carbon dioxide out of the atmosphere. Fine bits of degraded rangeland in southern Africa, South America, and Australia blow into the Southern Ocean, helping to sustain the rich biodiversity of those waters.

But dust from the Sahara also blows up onto the snowpack in the Alps, causing early melting. Pesticide-laden particles from central Asia’s shrunken Aral Sea are harming the respiratory health of people in the region, Okin says. Dust from northern China worsens the heavy pollution in Beijing. As in the American Southwest, population growth and changing climate are likely to make matters worse.

Owens Lake, which lies at the base of the eastern side of the Sierra Nevada in California, offers one glimpse of the connection between dust and development. Water diversions for Los Angeles left the lake bone-dry by 1920. By the 1930s, the Owens Lake playa was the largest source in North America of PM10: particulate matter measuring 10 micrometers or less, small enough to readily enter human lungs.

“The material that began to blow was also very high in arsenic, lead, lithium, antimony—some very bad things,” says Marith Reheis of the U.S. Geological Survey (USGS) in Denver. “You wouldn’t want to be downwind from Owens in a dust storm.” These chemicals are natural environmental toxins, a problem endemic with dust sources worldwide. In August 2005 a California superior court judge compelled Los Angeles to start putting water back into Owens Lake. Only then did the dust plague diminish.

As difficult as conditions have become in the Southwest, western China, the Australian outback, and too many other locations, the worst-case scenario is probably North Africa’s Lake Chad. This once important lake has seen its problems grow steadily worse as population and water use have increased over the past century. Today the Bodele Depression—the low point of the vast ancient basin in which modern Lake Chad lies—is the most active dust spot in the world.

It is not hard to identify what went wrong. The amount of water flowing through the principal rivers that feed into Lake Chad has declined by 73 percent over the last 40 years. Falling water levels have exposed fine-grained sediments along the periphery of the lake; high winds whip up those sediments into nasty clouds of dust that cause health problems for residents throughout the region. There is not enough moisture to recharge the groundwater; without that, thirsty plants are disappearing, making it likely that dust will only increase.

The dusty troubles of the American Southwest stretch all the way back to the mid-1800s. Before then, the landscape was largely stable grasslands. But the arrival of the railroads in the 1860s and 1870s enabled ranchers to put large numbers of grazing animals on public ranges. “They’d fatten them up and then put them back on the trains to be taken to Chicago and Omaha for slaughter,” says Painter. “For some time this was all free since there were no charges for public grazing.” The result of this four-legged invasion was dust. If you were standing up on the summit of Snowmass Peak above Aspen in the 1870s, he notes, you would have seen a slight tinge of dust on the snow at winter’s end. By the 1890s there was a much heavier stain.

Until disrupted, that dust had been a stable part of the local environment for thousands of years. Reheis has studied the dust covering much of the western United States, analyzing its chemical composition to determine where it came from. Much of the dust deposit east of the Rockies arrived in the last ice age, which ended some 11,000 years ago, when particles that had been ground up and transported by glaciers were deposited by meltwater streams. That fine-grained material was then eroded by the wind as the land dried. Dust produced during the glacial era made major contributions to the soil in the southern Midwest prairies, the most important agricultural region in the country today. “Windblown dust is part of normal soil building. Our whole breadbasket is dust,” Reheis says. “The most fertile stuff in the central Plains is all eolian [windborne] dust, most of which was deposited during the last glaciation.”

Prairie grasses that formed over these deposits did a good job of holding the landscape down, says William Schles­inger, a biogeochemist at the Cary Institute of Ecosystem Studies in Millbrook, New York, and one of Okin’s mentors. “Anything that can slow winds down so they can drop some of their load of silt, clay, and nutrients is good, and clumps of grass are perfect barriers,” he says.

Even when grasslands begin to diminish due to overgrazing and drought, biological and mineral crusts help keep soil stable, reports Jayne Belnap, a USGS research biologist in Moab, Utah. A well-developed biological crust is nearly immune to wind and water erosion. “It’s tough as nails against all wind forces,” she says. “Tests in wind tunnels of undisturbed crusts in the national parks show that biological crusts can withstand winds up to 100 miles per hour.”

Compressional forces, on the other hand—forces that are delivered vertically, such as the impacts of hooves, tires, and feet—can break up the soil and make it vulnerable to wind erosion. And therein lies the problem. Areas that are grazed or plowed may take decades to recover. Human development and off-road vehicles contribute to the degradation. As a result, the desert rangelands are losing their fine-grained material.

On a summer day with temperatures rising to about 105°F, I take a dusty ride with Greg Okin out to his research site at Jornada Experimental Range near Las Cruces. He is going to show me up close the damage that wind erosion is doing in this part of the country. “Shrubs used to occur on these former grasslands, but they were rare. Now they dominate,” he says.

Jornada encompasses some 250,000 verdant acres of native shrubs and grasses under wide blue skies in the Chihuahuan Desert. For the last 14 years Okin has come here to study how windborne dusts are changing the face of arid regions here, throughout America, and around the world.

The Chihuahuan Desert covers portions of New Mexico, Arizona, Texas, and north-central Mexico. The wind here normally blows toward the northeast. It is generally steady and strong in spring, but in summer it occasionally twists into a convection storm—a small, circular weather system that can direct brief but powerful gusts at the ground. These winds kick up fast-blowing dust storms that can envelop the unwary.

Okin, a wind erosion expert, tells me he got caught in one such storm just the other day on a dry lake bed. He was with researchers from the University of Texas who had set out portable wind tunnels to measure dust movement. Suddenly a fierce wind arose. “We were smelling dust, tasting dust, and couldn’t see anywhere,” he says. “I actually like dust storms, but when this one started attacking the Texas folks’ equipment, it just wasn’t fun anymore.”

Okin points out the rugged terrain, a green mosaic of vegetation. Mesquite bushes have migrated out from dry streambeds and the edges of dry lakes into the valley floor and flatlands. Creosote and mesquite have moved closer together, squeezing the grass in the middle. Grass is important here because it keeps the desert soils in place.

Okin first came here in 1996 to work with Schlesinger, who had been studying the Southwest desert’s gradual transition from grass to shrubs since the 1980s. Schlesinger noted that as the ecosystem changed, key nutrients in the soil—such as nitrogen, phosphorus, and various organic elements—accumulated beneath the canopies of the mesquite bushes, forming what he called islands of fertility and starving out the surrounding grasses.

Okin is now studying how winds scour nutrients from grassy areas and deposit them around shrubs, gradually killing off the grass and changing the desert from grassland to shrubland. He calls the wind-scoured areas between these shrubs “streets” and takes me to one area where these streets are well defined with fertile soils piled like dunes under mesquite bushes. “Once it gets that bad, there’s not much chance for grasses to recover,” he says.

Mesquite-covered dunes like these produce 10 times as much dust as do areas covered with native grass. I ask Okin how the whole process got started. Fire suppression is one prime cause. “Before Europeans moved into the territory, fires regularly moved across the landscape, killing shrubs but not grasses, which had evolved to burn, but not die, during the process,” he says.

Shrubs like mesquite and creosote grow too far apart to sustain wildfires, but grass acts as kindling to move the flames from one shrub to the next. Cattle grazing has also upset the balance by eliminating a lot of the grasses. “Cattle like grass but won’t eat shrubs,” Okin says. “They provide a selective pressure against grass and in favor of shrubs, while also depleting the grasses that sustained fires and killed shrubs.”

One hot morning I accompany Ed Fredrickson, a range scientist with the U.S. Department of Agriculture, to look at the Criollo cattle he has brought up from Mexico. He hopes they can solve some of the problems that English breeds have created. Criollo cattle are a desert-adapted breed that eats less and walks greater distances. Here they are less social, do not group up as tightly, and so distribute their footfalls more evenly across the landscape. They also weigh about 800 pounds, much less than the 1,200 typical of their English cousins. “English breeds have a lot of fat on their backs,” Fredrickson says. ”Butchers end up cutting that away. Cattle don’t need so much back fat in the desert.”

According to Fredrickson, cattlemen do not want to be blamed for turning grasslands into dust-choked desert. They also do not want to lose their livelihood. As their lands deteriorate, some have begun looking at their grazing practices and options such as Criollo cattle to take better care of the land.

Later I drive with Okin back to Jornada, dodging jackrabbits jumping out of the brush. Early land managers misstepped by poisoning coyotes. Without those predators, small mammals such as jackrabbits bred rapidly and devoured much of the local grasses. Today new threats loom. Okin points to dust swirling around a new housing development. These areas generate 100 times as much dust as desert covered with vegetation.

Okin takes me to a number of experiments testing ways to beat back the dust. The most promising approach uses eight-inch-tall fences called Con-Mods, which have been set up to stop large bare gaps from developing between shrubs. At each site where these chicken wire–like fences have been installed, leaves, twigs, and other plant materials are caught in the barriers, build up at the base, and enrich the ground between shrubs. “That litter is where grasses can get going again,” he says.

I ask if he really believes we can gain the upper hand on dust. He tells me that during the Dust Bowl era, when land managers saw their lands blowing away, they got together in 1934 and promoted the Taylor Grazing Act, which set strict limits on grazing activities in the western U.S. “What we did then is a model of what we can do today. We had a problem, we took action, and for a long time things got better,” he says.

Now we have a more difficult situation, with desertification under way at locations around the world. Nevertheless, in the American Southwest and perhaps elsewhere, Okin thinks that it may be feasible to slow or even reverse the process. “When erosion is allowed to deplete the resources in the soil, grasses just can’t compete with shrubs,” he says. “But if we can find ways to retard erosion and trap plant materials that start to move, natural ecological processes might help grasses come back. It might be an opportunity to turn an inexpensive method into grass recovery.”

Our future does not have to be a dusty one. A little chicken wire, better grazing practices, leaner cattle, controlled development, and fewer off-road vehicles could help restore the grasslands. The tide could turn against the dust, Okin says. “It could happen.”

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