Two years ago, 24 million tons of dust lifted high above Africa to create a cloud that swirled across the Atlantic Ocean and covered Puerto Rico. A meandering jet stream helped launch the monster dust cloud. The disappearance of biocrust, a mat that coats dryland soil and helps keep dust in place, wasfingered by ecologists as a factor in such storms.
Researchers say that the glue is likely to become weaker in the future because of climate change. The loss of biocrust in one area of the world can have wide-ranging and far- flung impacts, according to Rebecca Finger-Higgens, an ecologist at the U.S. Geological Survey.
A biocrust is a hard surface coating that contains a community of organisms. Historically, ecologists have paid little attention to biocrusts, which cover soils in arid, semiarid, and extremely cold places all over the world. Researchers have realized that these coating produce and process food that organisms need to thrive in arid environments. They help keep the soil moist.
Weber, Rodriguez-Caballero, and their colleagues mapped all of Earth's biocrusts, concluding they cover 12% of the land surface. Climate modelers and dust experts collaborated to figure out how much dust the biocrust glue currently averts. The researchers collected data about how much wind it takes to destroy the biocrust. They calculated dust emissions at 31 different sites, then fed the results into a model that predicted worldwide dust emission.
Weber and her team report that biocrusts reduce dust in the air by 700 million tons a year. All of New York City would be covered in 35 centimeters of dust. Maestre says that the study places biocrusts as key players in preventing dust emissions globally.
Between 25% and 40% of these crusts will disappear over the next 65 years according to Rodriguez-Caballero. Climate change that threatens soil organisms will account for half of the destruction. Other damage will come from trampling by humans, livestock, and farm machinery.
The impact of climate has been documented. In a long-term biannual survey of plots in Utah's Canyonlands National Park, they found that biocrust lichens suffer when temperatures increase. The team reported on 11 April in the Proceedings of the National Academy of Sciences that as Canyonlands temperatures rose, the lichens that help convert nitrogen in the air to a form that other organisms can use have almost disappeared. Finger-Higgens says that with less nitrogen, fewer plants can survive, leaving more bare ground and more dust emission.
Some implications of a dustier climate are not known. The impact of dust on temperatures depends on the size of the particles. Dust particles can cause snow to melt faster. Dust can make respiratory problems and other health issues worse for people.
Up to now, dusty places like the Sahel were expected to get less dusty as higher carbon dioxide levels have a fertilizing effect, but biocrust loss will likely counteract this process to some degree.
Michael Mann, an atmospheric scientist at Pennsylvania State University, University Park, says that climate modelers often overlook how biocrusts affect temperature and precipitation. He says that the effects of diminishing biocrusts shouldn't be dramatic enough to make a difference. There are large areas of the Earth for which we have no information about biocrusts, cautions Joseph Prospero, an atmospheric chemist at the University of Miami. That may change. Weber, Maestre, Finger-Higgens, and other biocrust experts are seeking funding for standardized measurements of biocrusts around the world.
The need to protect fragile communities is already clear. Reducing emissions and changing farming practices can help reverse the decline.
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