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Dust is made up of very tiny (about 1-10 µm) soil particles (fine silt and clay) and other fine particulate materials carried by wind on local to global scales. Because dust particles are so small, they can remain suspended in air for long periods of time. For this reason, dust may be transported across or between entire continents before being deposited, usually in rainfall. Dust is a form of wind erosion of soil; 40 percent of the soil eroded in the United States is eroded and transported by wind. Long-distance transport of dust can play a role in soil formation and development through the deposition of silt, clay, and soil nutrients and minerals. Scientists suspect that much of the calcium carbonate in the soils of the western United States was deposited by windblown dust. Windblown calcium carbonates and nutrients in dust originating in the Sahara Desert of northern Africa and deposited in the Amazon basin in South America are partly responsible for its fertile soils despite their high leaching rates.
Long-distance wind transport of dust can bury roads and fill drainage ditches; scour and damage fruit and vegetable crops, foliage, cars, and buildings; and choke coral reefs in shallow ocean waters. Viruses, bacteria, fungal spores, pollutants, and toxins transported to new areas in dust can cause illness to plants, humans, and other organisms. When inhaled, dust particles can lead to respiratory illnesses, and naturally occurring soil metals such as arsenic and mercury transmitted in dust can cause metal poisoning. Many fungal pathogens of crop and noncrop plant species are transmitted over long distances by windblown spores.
The Dust Bowl
One of the most memorable historical images in the North American psyche is the American Dustbowl, which lasted about 10 years during the 1930s. Poor land management that left soil bare, and combined with several consecutive years of drought to make soil extremely vulnerable to wind erosion. Regular dust storms in the U.S. Great Plains blew enormous dust clouds of silt, clay, and organic matter eastward into the Atlantic Ocean. Huge dark clouds of dust shrouded eastern states; it is said that the dust clouds over Washington, D.C., incited Congress to pass new laws to mitigate soil erosion.
Poor land management and overgrazing continue to intensify soil erosion around the world. Billions of tons of dust blow off of arid lands every year, and the dust blows into adjacent states and around the world. Dust storms in the desert southwestern United States are intensifying as recreational motor vehicle use and grazing increase, because these activities kick up dust and kill the natural cyanobacterial biological soil crusts that prevent erosion by binding surface soil particles together. High-altitude dust storms, from places as far apart from each other as Utah and China, deposit dust on snow packs in the Colorado Rockies and cause them to melt faster due to the decreased albedo of darker surfaces.
Faster and earlier snow melt feeds western rivers and reservoirs too quickly, causing them to overflow early in spring and run low late in the summer. This shift in timing has serious economic consequences for industries and communities that rely upon a steady flow of water throughout the summer. Dust from the Taklamakan Desert in China and the Sahara in Africa falls on the Swiss Alps, and Chinese and Mongolian mountain ranges receive dust from the Gobi Desert.
If the use of semi-arid lands intensifies with increased global human populations and agricultural land degradation, the intensity and frequency of dust storms and their far-reaching consequences will likely increase as well. Scientists will continue to study how the deposition of dust from faraway lands interacts with other consequences of global environmental change to affect human and natural communities.
- C. Brady and R.R. Weil, The Nature and Property of Soils (Prentice Hall Publishers, 2002);
- Harris, “Dust Storms Threaten Snow Packs,” National Public Radio, Morning Edition (May 30, 2006);
- Harris, “Stirring up Dust in the Desert,” National Public Radio, Morning Edition (May 31, 2006).