Abstract: Surface hydrology and soil erosion processes in arid and semiarid regions are affected by biological soil crusts (hereafter biocrusts) mainly through increasing soil surface roughness, which is of great importance but has not yet been fully investigated. In this study, we measured the surface roughness of bare sand, physical crusts, and biocrusts at different developmental stages (cyanobacteria, mixture of cyanobacteria and moss, and moss) by the chain method in a representative small watershed on the water-wind erosion crisscross region of the Loess Plateau. The surface roughness of biocrusts under different topography (slope gradient and direction) and soil conditions (soil types and water content) was investigated, and its correlations with the topographic factors and soil properties were analyzed. The results showed that soil surface roughness gradually increased from 0.67 to 16.76 (F=194.31, P<0.01) when the physical crusts, cyanobacteriabiocrusts, and cyanobacteriamoss biocrusts successively developed from the bare sand. Across all developmental stages, the cyanobacteriamoss biocrusts had the highest surface roughness (25 times of that of the uncrusted soil), while that of the moss biocrusts was decreased by 52.7% as compared with that of the cyanobacteriamoss biocrusts (but still higher than the bare sand and physical crusts). The surface roughness of biocrusts exhibited no significant differences among different slopes ranging from 10° to 30°, but it was significantly increased by 30.5% when the slope increased from 30° to 40° (F=10.05,P<0.01). Similarly, the surface roughness of biocrusts on the sunny slopes was 1.3 times of that on the shady slopes (t=-5.70, P<0.01). Furthermore, the surface roughness of biocrusts fluctuated greatly with increasing soil water content, with that developed on loessial soil being averagely 2.1 times (F=187.16, P<0.01) of that on aeolian soil under any water content. The surface roughness of biocrusts on the loessial soil was significantly negatively correlated with organic matter content (r=-0.998, P=0.04), but not with other soil properties. We concluded that biocrusts significantly increased soil surface roughness in the waterwind erosion crisscross region on the Loess Plateau, with developmental stage of the biocrusts, slope gradient, and slope direction being the key influencing factors.

Key words: energy consumption, economic growth, grey correlation analysis, Liaoning Province.