2.2 Biological soil crust sample collection
In this study, the undisturbed soil collection method was used to collect algae and moss crust-covered soil. The size of the undisturbed soil collection box used in the study was 50 cm×20 cm×15 cm. The four sides of the collection box were inserted into the soil as a whole to complete the fixation of the sample. The soil around the box was dug and the collection box was taken out containing the undisturbed soil. The box was closed at its bottom cover. The surface of the undisturbed soil sample was covered with a non-sticky plastic film to prevent soil damage and leakage. The soil sample assessed using a wind tunnel test. This study uses the point sampling frame to measure the BSC coverage of the soil (Li et al., 2010). Based on the 4 kinds of BSC coverage, in combination with the subsequent wind tunnel test, this study needs to repeat each measurement 3 times under 5 wind speed gradients. Therefore, 15 replicates of undisturbed soil samples for each coverage are ensured, setting up a statistically defensible experimental design. The classification of coverage is shown in Table 1.
Table 1. Coverage of biological soil crust