| Biological Soil Crusts(BSCs)can cover up to70%of the surface ground in thearid and semiarid regions,which is consisting of soil communities and cyanobacteria,lichens and mosses.They play a crucial role in carbon sequestration,nutrientaccumulation and water cycles in arid and semiarid ecosystems.The effects of BSCson water infiltration, erosion and runoff are complex and controversial,and very littleknowledge was received about the significant relationship between BSCs spatialpattern and water erosion.In order to explore how the BSCs affect soil loss and watererosion in the Chinese Loess Plateau,a typical loess hilly region in the Anjiagoucatchment of Gansu province was selected as the typical region in this study.BSCswere artificially cultivated in the field in the key water erosion region of loessplateau,China.Runoff and sediment yield were measured and recorded during the eachsimulated rainfall in the field.The major results were as follows.First, there is a significant impact on soil physical properties and the improvementof soil structure in0~10cm layer of the two types of the artificial BSCs(mosses andlichens) in this typical region.The results showed that the artificial BSCs increased thevolume weight of soil and decreased the total porosity and the capillary porosity,particularly at the upmost surface layers.During the development of biological soilcrusts,the proportion of the sand grain size was decreased and the silt wasincreased,the impact of BSCs on the clay grain size, however, was complex.Second, the infiltration rate and cumulative infiltration depth were both measuredin the plots where were covered by artificial BSCs or not. Results indicated that thetwo types of the artificial BSCs can both lower the initial infiltration ratesignificantly,and shorten the time to the stable infiltration rate.Infiltrationrate undermosses can reach stable status with a higher rate,while lichen crusts with a smallerone.The effect of the artificial BSCs on infiltration volume was bothpositive.Compared with bare soil conditions, mosses and lichens can increase thetotal infiltration with73.4%and12.7%respectively.Thirdly, it was feasible to inoculate and cultivate BSCs to conserve water and soilin the Loess Plateau,by using the method of broadcast sowing natural BSCs.BSCs,being as a significant indispensability part of the soil surface component,can markedly reduce water erosion potentials in the sloping conditions in the semiaridloess hilly region.Meanwhile, result also found that the reduction effect of overlandflow is more obvious than reduction in sediment.This is mainly dependent on thespecific types of BSCs and rainfall intensity.In general, soil and water retentioncapacities under mosses are better than the lichens, particularly under the influence ofrainfall events with lower intensities.Fourthly, the effect of artificial BSCs pattern on water erosion processes wasdetected and analyzed by the conduction of rainfall simulation experiments at themicro-plot scales.Our results showed that the spatial pattern and arrangement of BSCscan greatly reduce soil and water loss.The runoff volume and sediment yield underdifferent BSCs patterns were in the decreasing order of top congregate lichenpattern>top congregate moss pattern>bottom congregate lichen pattern>scatteredmoss pattern>bottom congregate moss pattern>scattered lichen pattern.This order wasmainly dependent on the spatial pattern of BSCs and rainfall intensity.Moss crustspatterns are better than lichen crusts patterns,and the function of keeping water andsoil is better in low intense rainfalls than in intense rainfalls.The most effective BSCsspatial patterns is scattered lichen pattern,which reduced90.6%of water loss and96.4%of soil loss in low rainfalls, while reduced65.2%of water loss and75.4%ofsoil loss in intense rainfalls. |
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