|Other Abstract||In arid region, soil water condition is the key factor for the desert ecosystem. Soil water infiltration capacity profoundly affects the redistribution of precipitation, and is of crucial importance for the storage and utilization of precipitation. The Gurbanttunggut Desert is the largest fixed and semi-fixed desert in China. It is covered by well-developed biological soil crusts( mosses, lichens, alage, fungi, cyanobacteria and bacteria). To explore the effects of BSCs on water infiltration plays an important role in revealing the characteristics of water circulation in this area. In this study, three typical types of biological soil crusts (moss, lichen and algal crusts) in the Gurbantunggut Desert were selected and sevaral experiments were used to examine the effect of biological soil crusts on the process of soil infiltration and evaporation. The results indicated that the effect of biological soil crusts on soil water infiltration was significant. Firstly, all three types of biological soil crusts decreased the initial infiltration rate significantly, but they differed in the degree of the reduction. The moss crusts, lichen crusts and algal crusts decreased the initial infiltration rates by 36.10%、46.42% and 50.39% respectively. The stable infiltration rate of sandy soil covered by the moss crusts, lichen crusts and algal crusts are as floow: 2.205-2.799 mm/min、1.622-2.283 mm/min and 1.128-2.254 mm/min. The moss, lichen（p<0.05）and algal crusts（p<0.05 also can decrease the stable infiltration rate by 16.50%、33.98% and 35.92% respectively. Secondly, movement of wetting front was slower in soils covered with these three types of biological soil crusts than in bare soil. The leakage time of soil under moss, lichen and algal crusts were respectively 2.13, 3.04, and 2.98 times that of bare soil. Thirdly, all three types of biological soil crusts reduced the cumulative infiltration volume. Relative to the bare soil, the reduction rates of moss, lichen and algal crusts are 16.10%、28.56% and 26.56% respectively.
The effect of biological soil crusts on soil water evaporation was also significant.
From may to september, the cumulative evaporation of sandy soil covered with the moss, lichen and algal crusts were 1.09, 1.14, and 1.01 times that of the naked soil. Over all, the sand covered by lichen crust has the strongest evaporation capability，and algal crust weakest. The moisture fixed in the BSCs maintain a higher rate of evaporation in a longer time, so most of them will loss through evaporation after precipitation. The soil covered by BSCs generally reduces the ability of precipitation that transform into the soil moisture.
In this experimental situation, the Kostiakov equation is most applicable to describe the infiltration processes of sandy soil covered by the three types of biological soil crusts, and the Horton equation was the next best option.|