4.1 Effects of coverage and wind speed on wind erosion and particulate matter emission of biological soil crusts
There are many factors affecting wind erosion and particulate matter emissions in the natural environment. Although the use of BSCs to cover the ground has a significant effect, being human damage the largest influencing factor (Neff et al., 2008). In this study, the areas covered by BSCs belong to areas with low population density, so wind speed and coverage have become the biggest factors affecting the wind erosion of BSCs and particulate matter emissions (Hong et al., 2020). Comparing and analyzing the factors influencing wind speed and coverage in Table 1 and Table 2, the influence of wind speed and coverage on the amount of wind erosion is similar, but the degree of influence on particulate matter emissions is quite different. Specifically, the influence of coverage is stronger than wind speed, and as the particle size decreases, the greater the influence of coverage and smaller the influence of wind speed, as shown in Figure 7. This phenomenon indicates that for BSCs, coverage is more important than wind speed, which is closely related to the nature of BSCs. Zou et al. (2018) summarized previous studies indicating that particles with a size of 0.05 mm to -0.5 mm are most likely to be eroded. The BSC can aggregate small particles in this size range to form more stable large soil particles through the cementation and adhesion of fungal hyphae (Eldridge and Greene, 1994). Xie et al. (2007) also believed that the biomass of BSCs is closely related to its erosion resistance. In addition, Spagnuolo et al. (2013) argue that the surface of moss has a strong ability to adsorb particles, and some of the particles with very small diameters can even interact with moss cells. Thus, moss can become an environmental indicator. Microbes in algae crusts have similar functions (Bailey et al., 1973). The previous studies can prove that the structure and properties of BSCs are more likely to affect the process of wind erosion and particulate matter emission. Therefore, under the assumption of less human interference, the surface particulate matter emissions of BSCs are more sensitive to coverage, followed by wind speed.
Figure7. Influence of wind speed and coverage in particulate matter emission