 The following is a production of New Mexico State University. Alive and dynamic, fragile and sensitive to change, the Earth's deserts offer us opportunity and challenge. Covering nearly one-third of the Earth's land surface, deserts contain resources that can help support and sustain today's rapidly growing populations. Yet to reap benefits from these fragile lands, their dynamics must be understood. How do climate and weather affect the nature of the land? How much human enterprise can desert soils support? Scientists conducting research on what has now become known as the desert project found that studying desert soils can yield an understanding of how deserts develop and change. Unlocking the past of these fragile ecosystems can help us understand the changes that are occurring today in deserts around the world. Until the 1950s, little scientific data had been gathered on desert soils. Instead, the bulk of scientific inquiry was on more agriculturally productive soils. Then, in 1957, the USDA Soil Conservation Service put science to work unlocking the secrets of the desert. For the next 15 years, a 400 square mile area here in southern New Mexico was, in a very real sense, put under a microscope. Soil scientists and geologists painstakingly map the types of soils and landscapes found in the area. Using radiometric and other techniques, they determine ages of various soils. Some as old as 2.5 million years, others less than 100 years old. Soils of the same age in different locations were compared and studied to find out why they were the same in some cases and in others, very different. During the desert project, an incredible amount of data was gathered. All this new knowledge documented five major concepts, concepts that are important for the way soil scientists around the world view arid lands. Just what are these concepts? First, arid lands are so fragile that they can degrade over a very few years due to human activity or even a very short period of drought. This process, called desertification, is a major concern around the world today. Second, looking over geologic time, that is, thousands to millions of years, natural climatic changes foster periodic desertification that radically alters the soil and the landscape. And third, the desert project researched a layer or horizon of desert soil that's common in arid regions around the world. It's a horizon that's cemented with calcium carbonate. It's this whitish horizon here. The desert project scientists found that much of the calcium in this calcium carbonate horizon did not originate from the local rock, but instead was brought in from the atmosphere in the forms of dust and rain. At the same time, they recognized that much of the clay in these desert soils are also brought in in the forms of dust and rain, like the calcium. The clay horizon in this case is the reddish horizon above the calcium carbonate horizon. And lastly, they recognized that whether or not this clay-rich reddish horizon forms at all in desert soils depends upon the amount of limestone in the original sediment in which the soils form. This is because there's a chemical reaction that takes place between the limestone and the clay. We wanted to pick a site to do this research that was representative of arid regions throughout really much of the world. The representative area and the variety of scientists and engineers that were asked to participate in the research led to a project that the ultimate result was a lot of spinoffs that have applications in the real world, third millennium real world. If you understand desert soils, if you understand their development over long periods of geologic time, you can move to other places and say, well, gee, this area is old, this area is young, and close at home, you don't build in a royal channel. You go out on the mesa to worry about wind-blown dust, but it's not going to wash away. If you're locating an area that you want to have stable for many tens of thousands or millions of years like a high-level or low-level radioactive waste site like the Nevada test site or the website, these in fact have used, these people working in those sites have in fact used desert project research in aspects of selection of those sites. Determining this history of landform development so we could get at how fast soils formed and all that was the side offshoot of that research allowed us to go in and start characterizing the aquifers. And there we're concerned not only about water supply, but how we can live with what Mother Nature gave us and how we can keep from polluting it with improper waste management. In many parts of the desert project, especially the basin floor where we are now, but also on the slopes going up to the mountains and the valley border, the desert is punctuated by sandy corpus dunes, seemingly held in place by dense bushes like this mesquite shrub. Now in 1857, a land surveyor walked this very land that we're on now. He made notes about the vegetation, he made notes about the condition of the landscape right at this section marker where I am now. He made no mention of dunes. Instead he described the land and vegetation like this, land level, sandy plain, some mesquite bushes, grama grass good. Aerial photos, some taken as early as the 1930s, show the same section corner. The dots that you see are thousands of corpus dunes. So in less than one lifetime, this major change in the desert had taken place. Grassy plain to corpus dunes. What happened? You really might say that the desert here suffered from an episode of information deprivation. Even though we've had humans living in this environment really for thousands of years, but in particular for the last three to four hundred years, we really didn't have a human presence or a strong component of agriculture in our deserts until really after the Civil War and the development of technologies that allowed people to use our desert lands, basically the ability to deliver water and stock water out onto the plains. And so people that were then expanding after the Civil War, the cattle industry in this region came from other environments and they really didn't understand the limits of an arid environment like the one here in New Mexico where ten inches of rain in a year is a lot of moisture. And by not understanding the limitations of this arid environment, the impact of that industry grazing in this area was huge and that impact was very severe and it really occurred in just a couple decades and it's well documented. We don't see those kinds of impacts today. People understand those limits much, much better. But we know that those impacts were huge and there was a lot of grazing and overgrazing in this country at the end of the last century. Desert Project scientists studied soil from the corpus dunes and by looking at the structure and age, they were able to piece together a scenario of the changes that had occurred to the landscape after the arrival of European livestock. Flat to rolling land was covered with gramma grass that efficiently used the limited rainfall. The cattle ate the grass and when it became scarce, they nibbled at the occasional mesquite, spreading mesquite seeds with their manure. As the mesquite spread and became more prominent in the area, it competed with the grass and won the fight for the limited moisture. With no grass to hold it, the sandy soil was blown by seasonal winds. In other places, grass was covered with sand and killed. The mesquite, however, put out more roots and continued to thrive. Overgrazing, of course, played a role in the desertification, the degradation of this environment that we've documented over the last century or so. But we know that it is just one player, one actor in this scenario. There are many in this complex environment. One of the things that we have learned over time is how important it is to maintain vegetation cover on these sites. And there's lots of different factors then, lots of different environmental influences, both human and natural, that can impact that vegetative cover. Overgrazing is one, but in particular in this environment is the effect of drought. We had substantial droughts in the 1890s, again in the teens, in the 1930s, of course, but a major drought in the 1950s, a six to seven year drought, probably the most severe drought in the last 350 years, had a huge impact in this environment. Really what we've learned from all this is that, besides this being very complex environments, that we have to understand that these environments have tremendous limits that are driven by their arid nature. We can't interact with these environments like they're farm ground in the Midwest, in Iowa. We have to understand natural processes that occur here. And when we think about trying to manage these systems sustainably, we have to work with those natural processes. And that's what I think a lot of research has generated, is knowledge about those processes and how we can utilize those processes in living sustainably in this arid environment. The knowledge that arid lands are fragile is increasingly important as population numbers grow and with the population comes pressure to develop arid areas around the globe. Scientists, governments and citizens are becoming more and more interested in finding ways to use the resources that deserts provide while sustaining those environments for future generations. During the desert project, scientists found evidence of soil changes, such as the formation of Copa stones, that formed in historically related events, such as overgrazing and drought. But they also found evidence of prehistoric desertification events that were probably related to alternating dry climates with wet climates. For example, the ridge behind me is a remnant of a Pleistocene fan. In theory, that fan would have formed during a dry period in the Pleistocene, when vegetative cover due to the dryness was very sparse and there was a lot of bare and exposed ground. So that during an episodic rainfall event, much water moved down the slope, carried the sediment with it and deposited the fan. Now during wetter periods, when there's more moisture, there's more vegetative cover and the landscape is then stabilized and erosion is curtailed. There's less erosion that takes place. And also in this environment, you have one Pleistocene fan and another Pleistocene fan and between those fans is a topographic low area. And in those topographic low areas are valley fields. There's sediments that record climatic changes that have occurred in the last 10,000 years during the Holocene. This is the spot where the Desert Project research team originally found charcoal in the early 1960s. And this particular bed has yielded carbon-14 ages from bits of charcoal like in this chuck that I'm holding here, ranging from about 7,000 years to about 4,500 years ago. And then we found another layer of charcoal right at the base of that very coarse gravelly layer that dated around 21 to 2200 years ago. And then across the arroil, there's a channel that cuts down through much of this section that's back filled with this kind of material. And it, at the base of that channel and in that channel is charcoal that's around 1,100 years old. So we have evidence of about three episodes of aridity, torrential rainfall. It is the hallmark of the Holocene. It's dry, poor vegetative cover, but you get these really major months, summer monsoons and the sediments from the older fans that are to the east and the mountain slopes are washed into these interfan valleys and gullies to the west, and they backfill them. And pollen work from these sediments and mollusks from these sediments indicate that this was a very dry climate. The finer grain intervals represent more of a grass vegetation. The coarser intervals represent a more shrub dominated vegetation, but all in the climate regime like we have today. And so this is kind of a Rosetta stone type site for the desert project. It's the key to a lot of our understanding of processes that go on in the desert. So the soils in this valley tell a story of three climatic changes that occurred in the last 10,000 years and the response of the landscape to those climatic changes. Of course, there were no scientists here thousands of years ago to document the gradual increases in temperature. If there had been, maybe they would talk of global warming and the impact that it would have on the world as they knew it. Today, some scientists think that the gradual increase in temperature that we've seen during this century is actually a natural increase in temperature, part of a natural cycle, just like the natural cycles that precipitated the deposition of the alluvial fans in this area. Other scientists argue that the increase in temperature is not natural, but instead it's the result of increased carbon dioxide emitted as the result of burning fossil fuels in our automobiles and in our factories. The jury is still out, but the research here in southern New Mexico desert made a large step in understanding natural cycles of climate change. Because of the fragile nature of these desert ecosystems, even subtle changes are recorded in the soils and landscape. The desert project helped unlock and read those records, and perhaps holds the key to understanding current and future climatic trends. When we think of desert soils, we commonly think of sand. And while many desert soils do contain a lot of sand, generally they are infinitely more diverse. For example, one of the major horizons that occur in desert soils around the world is the carbonate horizon. It's this whitish horizon here. It contains a lot of calcium carbonate. But the desert rocks in this soil contain little calcium. So where did all of this calcium carbonate come from? For 10 years, researchers working on the desert project set up dust traps during the windy seasons. They discovered that the dust blown into the area contained calcium, and rainwater itself contained dissolved calcium. During the rainy periods, water carried dissolved calcium into the soil. When the water evaporated, the calcium remained. It combined with the dissolved carbon dioxide in the soil pourers, forming calcium carbonate crystals that cling to sand and pebbles. At the same time, soil microorganisms were also creating calcium carbonate. With the process of respiration, carbon dioxide was released into the soil and excess calcium excreted by the microbes. This caused calcium carbonate to crystallize, forming shells on their external surfaces. So over thousands of years, tens of thousands, hundreds of thousands of years, the calcium carbonate crystals become so dense that they plug up the soil pour space. So they odor the soil, the denser and the thicker, the calcium carbonate horizon. Depth of carbonate accumulation in the soils is closely related to the amount of rainfall. This is shown by three soils that size four, five, and six, a transit from the arid to the semi-arid part of the desert project. The three soils are about the same age, several thousands of years old. Site four is in the arid part of the desert project. Elevation at this site is 4,350 feet, where it rains about eight inches per year. Here, the top of the carbonate horizon is at a depth of 10 inches and can be seen just above the one-foot marker on the tape. Site five is closer to the mountains and elevation is 4,730 feet. This soil receives several inches more rain per year than the soil at site four. Because of increased moisture, the carbonate horizon is deeper. Here, it's top is at 20 inches, compared to 10 inches at the more arid site four. At site six in Soledad Canyon of the Oregon Mountains, elevation is 5,700 feet and rainfall is nearly 16 inches per year. Here, the carbonate horizon is still deeper and its top is below 41 inches. All three soils are about the same age and have formed in the same kind of sediments derived from the Oregon Mountains. As we move from 4,350 feet to 5,700 feet in elevation, the only factor that changes is the rainfall. This shows that increasing rainfall gradually moves carbonate deeper into the soil. In older soils, the relation between carbonate depth and rainfall are more complicated but still evident. For example, soils in the arid zone and of middle places in age have stage four carbonate horizons in which the carbonate horizon is plugged with carbonate and has a laminar zone at its top. In contrast, soils of the same age in the semi-arid mountains have stage one carbonate in which carbonate occurs only as thin coatings on pebbles. The notion of calcium and desert soils combining with atmospheric CO2 to make calcium carbonate may have radical importance for questions people are asking today about global warming. Just what is the role of desert soils in the emissions of CO2 given off by automobiles and factories? Well, two things. First, desert soils may be a sink for atmospheric carbon dioxide, but on the other hand, they're a source for atmospheric carbon dioxide. This is because when you put acid on carbonate, carbon dioxide bubbles are given off. Well, the same thing happened when acidic rain comes into contact with exposed calcium carbonate. It's the same process occurring in cases and deserts around the world where exposed carbonate horizons contact with acidic rain. We don't yet know the answers. Additional research on soils that are sensitive to climate change may help us find the answers to questions of environmental importance to us all. Another important component of desert soils in addition to calcium carbonate is clay. Individual clay particles are so small that they can't be seen without the aid and the microscope. Early in this century, it was generally believed that clay was formed through the weathering process. That is, over the years, wind and rain gradually decomposed rocks and sediments into smaller and smaller and finer and finer particles. Through the desert project, scientists discovered that, like the carbonate in desert soils, much of the clay also comes from the atmosphere. Blown in from elsewhere as fine dust that settles onto the landscape. During seasonal rains, the clay particles percolate into the soil, gradually accumulating in the pore space in the soil to form a clay layer or horizon. At lower elevations, the clay horizon is just above or slightly into the calcium carbonate layer. As you move mountainward and precipitation increases, the clay layer becomes thicker. Scientists believe what happens in deserts is that both the calcium and the clay move downward into the soil with moisture. The clay particles suspended in water, the calcium dissolved in water. Because the calcium is dissolved, it moves deep into the soil. When the water evaporates, the calcium stays behind, forming the carbonate horizon. With the clay horizon just above it. Those scientists who worked on the desert project were sometimes asked, with thousands of square miles of desert in the United States alone, why was this particular area of desert in the southern New Mexico chosen for study? The answer is because many features of deserts around the world are found in this region. And that the effects of parent material, time, topography, vegetation, and climate can be studied in this area and then applied to other areas. For example, the area contains semi-arid mountains as well as arid basins between the mountains. So scientists can study how differences in climate and topography affect soils of the same age and from the same parent materials. The area also has a river valley. Its soils and landscapes can be compared to those of the basins and mountains. And lastly, the area has many landforms typical of arid regions. These were created when materials were deposited by river water or by erosion from the mountains upslope. Those materials deposited by moving water are called alluvium. They are the parent materials from which the area's soils were formed. Just like your traits and characteristics are dependent upon those of your parents, a soil also inherits traits from its parent material. Especially important is the chemistry of the parent material. Soils formed from the Oregon Mountains and the Doniana Mountains tend to have red clay horizons. In contrast, soils formed from alluvium derived from the San Andres and Robledo Mountains lack this red clay horizon. They're both the same age. So why does one have a clay horizon and one not have a clay horizon? The answer lies in the parent material. The soils that form from alluvium downslope from the Robledos and the San Andres are high in calcium carbonate, like limestone. One theory for the difference is that a striking chemical reaction occurs between the clay and the abundant calcium. This unique chemistry causes the clay particles to clump together and stick to the calcium-rich soil particles. So in the case of soils formed in limestone alluvium, the clay stays mixed in with the soil as percolating water travels through the soil the clay does not move with the water and it does not separate out into horizons. Now in the case of igneous soils like we have here, there isn't as much calcium to keep the clay stuck together, flocculated. So in that case, the clay can move with the percolating water and it can separate out into these reddish brown clay-rich horizons. In the late 1800s, soil scientists making maps of soils in Russia recognized that there were many different types of soils and that each soil type was repeatedly found in unique situations. And in those unique situations, the soils were a function of parent material, of vegetation, of climate, of topography and the age of the land. That was the beginning of modern soil taxonomy, the study of soils as an organized, natural body or system. Since then, scientists have added many new discoveries to our knowledge of soil. Each addition helps as we make decisions about how to use and sustain our natural resources. The pioneering efforts of scientists who worked on the desert project added invaluable information to this body of knowledge. We now know that the desert is so fragile that even very small changes in climate and activity can trigger desertification. That periodic global warming triggered major episodes of desertification that radically changed the soils and landscape. And that significant amounts of calcium and clay were transported into desert soils from dust and rain. Parent materials, especially those containing limestone, yielded chemical reactions between calcium and clay that changed the soil in different ways. As global population increases, the need for resources and space puts pressure on once unoccupied and little used arid lands. The knowledge yielded by the desert project and research that builds on this knowledge can help decision makers understand the impact of our decisions and make wise ones for the future. The preceding was a production of New Mexico State University. The views and opinions in this program are those of the author and do not necessarily represent the views and opinions of the NMSU Board of Regents.