| Biological soil crust (biocrusts) extensively developed in the Loess Plateau region afterthe “Grain for Green” eco-project was implemented in the region. So far, studies on theroughness of biocrusts in the Loess Plateau region were fresh. Aimed to determine theinfluencing factors of the temporal-spatial distribution characteristics on the surfaceroughness, the study investigated the surface roughness of soil with biocrusts at their differentsuccessional stages by using the chain method. Besides, the impact of slope aspects, soilwater content, freezing and thawing, biological composition and soil physical properties onsurface roughness were also investigated. We analyzed different testing methods of roughnessand their applicabilities. The effect of different roughness of biocrusts on runoff generatedprocess on slope land were studied by the method of pouring water scouring experiment underthe same flow and plot conditions. The paper was aimed at understanding effect of differentbiocrusts roughness on runoff generated process on slope land, and complementing runoffgeneration. As far as our knowledge, the paper was the one of the earliest studies on biocrustsroughness in the Loess Plateau region. The main results are as follows.(1) Soil surface roughness was decreased at the initial successional stage of biocrustsand it was increased along with biocrusts’ development in the region. Soil roughness wastended to be stable since biocrusts developed ten years later and was different dependingon the season. When development of the soil surface roughness on biocrusts had becomemore stable, the sloped aspects has no influence on it, but the differences existing on thedifferent the slope position. Soil surface roughness was decreased to56.81percent after9months rehabilitated and reached to3.44. The roughness of biocrusts was to get an26.9percent reduction within5years rehabilitated and it was increased along with biocrusts’development in the region. Soil roughness was tended to be stable since biocrusts developedten years later. The roughness of biocrusts also changed with seasons, and it decreased in thespring about8.6%lower than winter. When development of the soil surface roughness onbiocrusts had become more stable, the different sloped aspect was not significant. But theslope position was different. The roughness of biocrusts which at low slope decreased10.6%compared to middle slope and reached to7.25. (2) Roughness of biocrusts was related to soil water content, freezing and thawing,the composition of biocrusts, Bryophytes Coverage and the measures. Soil moisturesignificantly impacts surface roughness. The surface roughness of BSCs changed obviouslywith soil moisture variety in the early development. However, it showed slightly change forthe late successional BSCs. Freezing-thawing also affected surface roughness with BSCs.Roughness was more susceptible to freezing-thawing in the early development, which showed29.7%increased compared with bare soil. The surface roughness of late successional BSCsexhibit slightly changes only after repeated freezing-thawing. The surface roughness of BSCsshowed a statistically significant relation-ship with the coverage of moss（P<0.1）Indetermining the roughness, result varies from different methods. Soil rugosimeter was moreapplicable to measuring between patches, and the chain methed was fit for determining withinpatches.3D laser scanner with a1mm precision failed to reflect the difference of roughnesswith variable biological composition.(3)When roughness of biocrusts exceed a certain restriction under the condition of2L/min flow，the runoff depth shot up and duration time of runoff considerablyreduced. The roughness on BSCs with different biological components showed a statisticallysignificant relation-ship with the runoff depth and duration time of runoff（P<0.1）. Therunoff depth hold basically steady within biocrusts’ roughness index from4to10, butincreased47.2%within biocrusts’ roughness index above10. The duration time of runoff holdbasically steady within biocrusts’ roughness index from4to8, and decreased39.1%withinbiocrusts’ roughness index above8. By biocrusts itself, bryophytes coverage showed astatistically significant relation-ship with the runoff velocity and starting time of runoff（P<0.1）. And cyanobacteria coverage showed a statistically significant relation-ship withthe starting time of runoff （P<0.1）. |
PDF Full Text Request