Soil Water Infiltration Characteristics And Model Simulation Of Biological Soil Crusts Based On The Line Source Infiltration Method

After the implementation of the project of returning slope farmland to forest?grass?,biological soil crusts is widely developed on the surface of the returned farmland in the Hilly Loess Plateau region.The average coverage of biological soil crusts in the region can reach60%?70%or even higher,which significantly affects the soil water infiltration and slope runoff of the returned farmland.It is of great significance to clarify the effect of biological soil crusts on water permeability of returned farmland and the hydrological effect of returning farmland to forest?grass?in this area.At present,there are still some shortcomings in the method of determining the water infiltration rate in the soil water infiltration of biological soil crusts distributed on slopes,which hinders people's understanding of the influence of biological soil crusts on the hydrological process.Linear source infiltration method?hereinafter referred to as linear source method?is a method proposed by Tingwu Lei et al.according to the principle of water balance,which can accurately and simply determine the soil water infiltration rate of sloping land under different conditions.In this paper,the effects of soil slope,water discharge rate and soil water content on the determination of soil water infiltration rate by line source method were studied.The applicability of line source infiltration method in the study of biological soil crusts permeability of sloping land was studied with the artificial simulated rainfall test as the reference.Based on the statistical analysis methods such as correlation analysis,principal component analysis,regression analysis,and path analysis,the mechanism of water permeability of biological soil crusts was analyzed.Based on the existing theory of layered soil water infiltration model and the characteristics of biological soil crusts,the parameters of Green-Ampt layered soil water infiltration model were revised,and a soil water infiltration model with biological soil crusts was constructed.The study is of great significance to accurately understand the soil hydrological effect of biological soil crusts on farmland in Hilly Loess Plateau region,and provides a scientific tool for the evaluation of soil and water conservation benefits of the project of returning farmland to forest?grass?in this area.The main conclusions are as follows:?1?Slope and water discharge rate are the key factors affecting the determination results of line source method.The effect of excessive soil water content on the observation of line source method can be eliminated by adding dye into the infiltration water.The line source method can be used for the determination of soil water infiltration rate of biological crust on slope land with a slope of 10°?35°.Within the slope range,line source method measure the initial infiltration rate range of 10 mm/min-4 mm/min,the average infiltration rate range is 2.2 mm/min-1.3 mm/min,the steady infiltration rate range is 1.8mm/min-0.8 mm/min,slope increase line source method to measure the initial,average,steady infiltration rate were significantly decreased.The discharge rate of the water distributor increased from 150ml/min to 450ml/min.The initial infiltration rate measured by the line source method increased from 6mm/min to 9mm/min.The average infiltration rate increased from 2.0mm/min to 4.0mm/min.The steady infiltration rate increased from1.0mm/min to 2.0mm/min.The initial soil water content increased from 8%to 24%,the initial infiltration rate measured by the linear source method decreased from 16mm/min to4mm/min,the average infiltration rate decreased from 4.0 to 1.5mm/min,and the steady infiltration rate decreased from 2.3mm/min to 1.2mm/min.The initial soil water content increased,and the measured initial,average and steady infiltration rates significantly decreased.As for slope change,the initial,average and stable infiltration rates measured by line source method were significantly reduced.The regression equation y₁=-0.1712x+11.273R²=0.7852 p<0.05 y₂=-0.0332x+2.1782 R²=0.7466 p<0.05 the measured values of initial and steady infiltration rates obtained by the line source method with different slopes were corrected respectively.The initial,average and steady infiltration rates of soil water measured by the line source method changed significantly with the change of water discharge rate.In the implementation of line source method,the specific discharge rate should be selected according to the local conditions and the influence of different factors should be considered.For the Hilly Loess Plateau region,300ml/min is an appropriate discharge rate.When the soil pre-water content is greater than 18%,4g/L coomath blue is added to prepare the solution to clearly distinguish the boundary of the dry and wet areas of the soil.?2?Under the condition of line source method,the initial,average and steady infiltration rates of soil water showed an increasing trend with the increase of the development degree of biological soil crusts.With the increase of the total coverage of biological soil crusts,the initial and average infiltration rate of soil water decreased significantly,while the steady infiltration rate increased significantly.With different coverage of moss,the growth degree increases,the initial infiltration rate of biological soil crusts measured by the line source method increased from 3mm/min to12mm/min,the average infiltration rate increased from 0.5mm/min to 4.5mm/min,and the range of stable infiltration rate was 0.3-1.8mm/min.The total coverage of biological soil crusts increased,the initial infiltration rate was reduced from 10mm/min to 4mm/min,the average infiltration rate was reduced from 2.2mm/min to 1.8mm/min,and the stable infiltration rate was increased from 0.9mm/min to 1.3mm/min.The initial infiltration rate was bare soil?28 mm/min?>moss crust?12 mm/min?>cyanobacteria crust?4 mm/min?,and the soil water infiltration rate of algae crusts in the whole infiltration process was lower than that in the moss crusts and bare soil plots.?3?The line source method can well describe the soil water infiltration process of different types of biological soil crusts in sloping land,and it has a significant linear correlation with the steady infiltration rate measured by artificial simulated rainfall test.Under the artificial simulated rainfall measurement,the average infiltration rate of the growth degree of biological soil crusts increased with a range of 0.9mm/min-1.4mm/min,and that of the stable infiltration rate increased with a range of 0.8mm/min-1.3mm/min.Both the average and stable rates showed an increasing trend,with no significant difference among the treatments.Line source method can reflect the complete biological crust with a slope initial,average and stability of the soil infiltration rate and its measurement results with the same test area measured by artificial rainfall simulation steady infiltration rate had significant linear correlation between y=1.73 x-1.24?p<0.05?,the line source method can accurately determine the natural rainfall soil water infiltration rate under the condition of biological soil crusts.?4?The initial infiltration rate of soil water in biological soil crusts was negatively correlated with the coverage of algae crust?R²=0.905 P<0.01?,and the stable infiltration rate was negatively correlated with the density of subsoil?R²=0.738 P<0.01?.The main influencing factors of soil water infiltration of biological soil crusts were crusts coverage,crusts bulk density and substratum bulk density,with a cumulative contribution rate of 74.73%.The initial infiltration rate of biological soil crusts was mainly determined by the coverage of algae crust.The stable infiltration rate was mainly determined by the bulk density of the subsoil,which increased with a contribution rate of 60.68%.?5?Green-Ampt model of soil water infiltration in biological soil crusts.The original model and the improved model,respectively,compared with the measured results of line source method analysis,the improved Green-Ampt model4)= increased by 21.03%,can be more accurate simulation of biological soil crusts water infiltration,lay the foundation for the research of biological soil crusts hydrological effect.