When bacteria, fungi, mosses, lichens and algae combine on dry land, they form so-called biological soil crusts. These cover about twelve percent of the total global land surface, and up to one third of the surface in dry areas. Biological soil crusts play an important role in consolidating soils, making them more stable and less likely to be stirred up by the wind. Since dust particles in the atmosphere have an impact on the climate, soil crusts fulfil an important function in several respects. In a paper published in Nature Geoscience, biologist Bettina Weber of the University of Graz and her colleagues provide, for the first time, comprehensive facts and figures on the importance of biological soil crusts for the regional and global dust cycle, both under current and future conditions.
The largest areas with biological crusts are in Africa, the Middle East and Asia, Australia and the Midwest of the USA. However, they can be found worldwide wherever temperature, rainfall and soil conditions are suitable. Describing her results, Weber says, "We estimate that biological soil crusts reduce global atmospheric dust emissions by about 60 percent." However, by 2070, the authors expect biocrust cover to decrease due to climate change and intensification of land use, with declines of 25 to 40 percent depending on the scenario. As a result, more dust will enter the atmosphere – with various effects.
"On the one hand, dust has climatic effects, as water condenses or ice crystals form on the dust particles, which influences precipitation patterns," Weber explains. Dust also has a cooling effect in the lower atmosphere by reducing solar radiation. "According to our calculations, this corresponds to about half of the cooling effect of aerosols released by humans – for example, through the burning of fossil fuels and biomass," adds the researcher.
On the other hand, dust transports nutrients that, if blown away, are lost from the local site, and can have a fertilising effect in the target area. In barren areas in particular, the nutrient input can cause damage that ultimately displaces the original vegetation. Sand also carries microorganisms that colonise newly formed and existing habitats. "In the process, pathogens can spread and harm plants, animals or humans," Weber explains as another connection. Thus, the loss of soil crusts poses a potential risk to climate, environment and health.
The researchers obtained their results by combining measurement data on biological soil crusts with a global climate model. In this way, they calculated the current importance of biocrusts and simulated various future scenarios. This clearly showed the essential function of biological soil crusts. Therefore, these effects should be taken into account in future modelling of global change, in measures to mitigate climate change and in the design of adaptation strategies, the scientists recommend.
Publication:
Global cycling and climate effects of aeolian dust controlled by biological soil crusts
Emilio Rodriguez-Caballero, Tanja Stanelle, Sabine Egerer, Yafang Cheng, Hang Su, Yolanda Canton, Jayne Belnap, Meinrat O. Andreae, Ina Tegen, Christian Reick, Ulrich Pöschl, Bettina Weber
Nature Geoscience, DOI 10.1038/s41561-022-00942-1
