Two years ago, 24 million tons of dust rose high above Africa, forming a cloud that swirled across the Atlantic, cloaking Puerto Rico in a pink patina. An unusually meandering jet stream contributed to the formation of the monstrous dust cloud. But now ecologists have identified another contributing factor to such storms: the disappearance of the “biocrust,” a microbial mat that covers the dry soil and keeps dust in place.
A biocrust is a hard surface coating, or “skin,” typically a few millimeters thick, that contains a thriving community of fungi, lichens, mosses, cyanobacteria, and other microbes. “It glues the sand together,” says Bettina Weber, an ecologist at the University of Graz and a co-author the in NatureGeoscience published study. But trampled on by cattle and destroyed as a result of climate change, this glue is likely to weaken in the future, leaving the soil prey to the wind. The dust study shows “that the loss of biocrust in a given area of the world can have far-reaching implications,” said Rebecca Finger-Higgens, an ecologist at the US Geological Survey.
Biocrust in the Australian state of New South Wales.
(Photo: David Eldridge, UNSW)
Until now, ecologists have paid little attention to the biocrusts that cover soils in arid, semi-arid, and extremely cold regions around the world. However, researchers have realized that these layers produce and process nutrients that other organisms in the area need to thrive, especially in arid environments. They also help dry soils retain their low moisture levels.
In 2018, Weber and her colleagues mapped all of Earth’s biocrusts and concluded that they cover 12 percent of the land surface. They then teamed up with climate modellers and dust experts to find out how much dust formation the biocrust glue currently prevents. First, the researchers determined which wind is needed to destroy the biocrust and blow away the soil. Then they calculated dust emissions at 31 different locations and fed the results into a model of global dust levels – and how much it would increase without the biocrust.
According to Weber and her team, biocrusts reduce dust pollution in the air by 700 million tons per year. That amount would bury all of New York under 14 inches of dust. The study shows “that biocrusts play a key role in preventing dust emissions worldwide,” says Fernando Maestre, a dryland ecologist at the University of Alicante.
Dust can aggravate respiratory problems and other ailments
Dust storms like the one that devastated cities in southeastern Brazil in 2021 could become more frequent as soils in arid regions retain less moisture. Between 25 and 40 percent of these crusts will disappear in the next 65 years, says Emilio Rodriguez-Caballero, who was involved in the study and now works at the University of Almeria. On the one hand, climate change threatens soil organisms, it could cause about half of the destruction. The crusts are also trampled on by people and livestock or get under the wheels of agricultural machinery.
Finger-Higgens and colleagues have documented the effects of climate in more detail. In a long-term study of areas in Canyonlands National Park in Utah, they found that biocrust lichens in particular suffer from rising temperatures. As temperatures in the Canyonlands have risen by 0.27 degrees Celsius per decade, lichens, particularly those that help convert the nitrogen in the air into a form that other organisms can use, have all but disappeared. the team reported in the specialist magazine in April PNAS.
Fewer plants can survive with less nitrogen, resulting in bare soil and more dust emissions, according to Finger-Higgens. According to the researchers, some effects of a dustier climate are still unclear. The influence of dust on temperatures depends in part on the size of the particles. Dust particles serve as nuclei for cloud formation and can cause snow to melt faster. While dust helps transport essential nutrients for plant life, it can aggravate respiratory problems and other health conditions in humans.
Previously, it was assumed that dusty areas like the Sahel would become greener and less dusty because higher levels of carbon dioxide have a fertilizing effect. But the loss of biocrust will likely counteract this process to some extent, Weber and her colleagues note.
Climate modelers have often neglected how dust affects temperature and precipitation, says Michael Mann, an atmospheric researcher at Pennsylvania State University. However, the effects of the disappearing biocrusts should not be so dramatic that they make a big difference in global climate models, he says.
However, Joseph Prospero, an atmospheric chemist at the University of Miami, warns that there are large areas on Earth for which information about biocrusts is scarce. Weber, Maestre, Finger-Higgens and other experts are now trying to fund biocrustal measurements around the world.
According to the researchers, the need to protect these vulnerable communities is already clear. Reducing emissions and changing agricultural and other land-use practices can help halt their decline, says Maestre. “The results make a strong case for protecting biocrust around the world.”
This post is in the original in the science magazine Science published, published by the AAAS. German editing: cvei