Water Repellency of Biological Soil Crusts and Influencing Factors on the Southeast Fringe of the Tengger Desert, North-Central China

Biological soil crusts (BSC) have key roles in hydrological and ecological processes in arid desert areas. Water repellency (WR) of BSC is an important property because it modifies the local hydrological regimes and affects ecosystemfunctions. However, the variations ofWR in different types of BSC and the temporal variations under field condition are relatively unknown. Actual WR of four types of BSC and mobile sand were observed sequentially after heavy rainfall using the water drop penetration time test. The development of BSC on the surface of stabilized sand dune markedly promotes WR. The WR of four types of BSC variation across time was influenced by environmental factors under field conditions. The WR increased as soil moisture content or air relative humidity increased up to a level above which WR decreased. However, the peak levels varied between the different types of crusts. For surface temperature of BSC and air temperature, the WR of the four types of BSC decreased with increasing temperature. Our results demonstrate that the WR of BSC in arid desert ecosystems depends greatly on the developmental stages of the crusts, as well as environmental factors, such as antecedent topsoil moisture conditions, relative humidity, surface temperature, and air temperature.