The Effect Of Biological Soil Crusts On Water Infiltration And Simulation In Hilly And Gully Region Of The Loess Plateau

Biological soil crust (biocrusts) extensively developed after the Grain for Greeneco-project was implementated in the Loess Plateau region, there is a large area ofbiocrusts in the region. So far, we had not clearly known what and how the biocrusts,which were in different successional stages, had an effect on water infiltration. In the study,soil hydraulic and infiltration parameters of biocrusts in different successional stages weremeasured and analyzed so as to determiner effect of biocrusts in different successionalstages on water infiltration. Then the process of water infiltration was simulated. The studywas aimed at clarifying and definiting the role of biocrust played on water infiltrationprocess. The study may benifit effective management of biocrusts, rational utilization ofwater and soil resources to promote vegetation restoration, promote the healthydevelopment of the ecosystem. The results were as follows.(1) The formation of biocrusts lead to an increase of soil water repellence (SWR)markedly. The SWR showed a decrease trend along with the succession of biocrusts.Soil moisture content and the composition of biocrusts were the major influencefactors of SWR.No SWR was observed on the loessal soil without bioctrust in Hilly and Gully Regionof the Loess Plateau. However, a slight SWR was developed on soil when biocrustspresented, both in the intensity and persistence. SWR of biocrusts showed a decrease trendalong with the succession of biocrusts. SWR of biocrusts with the moss coverage above20%was significantly lower than that of cyanobacterial crusts. SWR of biocrusts wasrelated to soil moisture and dominant species. SWR increased against the decrease of soilwater content for moss dominated biocrusts, while there was a bimodal curve as thedecrease of soil water content for the cyanobacterial biocrusts. For the light cyanobacterialcrust, SWR approached the maximum value at40%of field water holding capacity. While for the other four stages of biocrusts, which were dark cyanobacterial crust,cyanobacterial and little moss crust, moss and little cyanobacterial crust as well as themoss dominated crust, SWR reached the maximum value at20%of field water holdingcapacity.(2) Soil water retention and moisture availability were increased with thepresentation of biocrusts. Soil water retention increased after the formation of biocrust,along with the soil moisture availability. But the soil water retention and soil moistureavailability decreased during the development of biocrusts.(3) Biocrusts showed an effect on the process of water infiltration, the range ofeffection was subject to the matrix soil. Meanwhile, the interaction between biocrustsand matrix soil effected the the process of water infiltration. Water infiltration rate wasreduced with biocrusts, the descent range relaxed as the succession of biocrust. Theinfluence of biocrust on water infiltration process varied with the change of matrix soil.(4) Water infiltration process of Loessal soil covered with biocrusts can besimulated by the revised Green-Ampt model. The model fitting infiltration rate ofsoil covered with biocrusts were consistent with the measured values except for soilcovered with light cyanobacterial crust. For the revised Green-Ampt model, biocrustshad an efffect on water infiltration process, boiled down to the influence of soil hydraulicconductivity, and the water infiltration process is controlled by layer of biocrusts. Theenergy dynamics theory of water infiltration process of biocrust covered on Aeolian sandysoil and Lou soil were more complex than that on Loessal soil, so further research wasneeded.