Regulation effect of microbiotic crusts on soil hydrological processes in shapotou revegetation-fixed sand dune regions

Abstract

Microbiotic crusts (MC), also called biological soil crusts, cryptogamic crusts, mostly formed by cyanobacteria, green algae, lichens, and mosses, are widespread in arid and semiarid zones and well developed in a revegetation-fixed sand area of Shapotou, southeastern edge of Tengger desert, Northwest China. They lie adjacent to completely bare sand dunes, provide a loam cap for the structureless aeolian sand, and have greatly altered the hydrophysical properties of the topsoil in the regions, which would consequentially affect the soil hydrological processes. Soil hydrological process of MC has been a most debated problem with so much academic concerns all along. This paper introduced the results gained in studies of the regulation effect of MC on soil hydrological processes such as precipitation penetration, soil water redistribution and surface evaporation, through synthetic analysis of serial field ecological investigation, experimental analysis of MC's hydrological properties, and soil hydrodynamics experiment under simulated precipitation in field as well as dynamic monitoring of soil water content in profiles of different vegetation-fixed and mobile sand dune regions after natural precipitation. Some results are as follows: (1) MC not only reduced the speed and depth of water penetration but also induced the instability of wetting front showed by appearance of finger flow in the water transition zone. (2) The year-by-year development of MC resulted in significant variations of process patterns of soil water distribution. Water redistribution in sand dune profile presented a trend toward top layer, showing an obvious effect of MC on precipitation interception. (3) MC greatly increased surface evaporation by reducing reflectivity and enhanced soil capillarity. The regulation effect of MC on soil hydrological process is deeply changing the soil water environment of this rainfed revegetation ecosystem in the sand dune regions, which might partly interpret the cause of the degraded vegetation ecosystem.