A ‘Living Skin’ is Protecting the Great Wall of China From Erosion
taylorvich writes:
https://www.science.org/content/article/living-skin-protecting-great-wall-china-erosion
The Great Wall of China used to be much greater. What stands today is only a fraction of the expansive fortifications built on the country's northern borders starting more than 2000 years ago and then eroded by time. But many sections of the remaining walls seem to be getting preservation help from an unlikely source: thin layers of bacteria, moss, lichen, and other organisms known as biocrusts, which grow on the surface of soils.
A study published today in Science Advances finds that these so-called "living skins" have likely protected parts of the Great Wall from wind, rain, and other corrosive forces. And with advances in technology and research, scientists might eventually propagate new biocrusts to spare the wall from further degradation.
The work is "innovative and creative," says Nichole Barger, an ecologist at the Nature Conservancy who was not involved in the new research. She notes it's not necessarily surprising, however, given the growing recognition of the protective effects of biocrusts: These webs of growth are known to help stabilize dryland ecosystems and prevent soil erosion.
Many of the Great Wall's most well-known and visited sections are made of stone or brick, but other parts were built out of soil compacted by workers, often called rammed earth. Over time, this material can break down as rain seeps in, wind blows the soil away, salt crystals form inside, and temperatures fluctuate.
But this compacted soil, much like the natural soils surrounding it, can also become home to biocrusts. These layers of growth have been estimated to cover some 12% of the planet's land surface, and are concentrated in regions with drier climates, including northern China. They come in a variety of forms, from thin networks of bacteria mere millimeters thick to denser layers of moss and lichen up to a few centimeters in height.
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The researchers suggest these properties and others linked to biocrusts protect the Great Wall from degradation in a few ways, including by reducing wind erosion, preventing water and salt from seeping in, and increasing the overall stability of the rammed earth. Perhaps unsurprisingly, thicker, moss-dominated biocrusts were generally more protective than thinner ones dominated by cyanobacteria.
Journal Reference:
Yousong Cao et al., Biocrusts protect the Great Wall of China from erosion, Sci. Adv., 8 Dec 2023, Vol 9, Issue 49 DOI: 10.1126/sciadv.adk5892
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