Study On Characteristics Of Preferential Flow On Three Types Of Land Use In Northern Beijing

As a common movement form of soil moisture,preferential flow is closely related to soil nutrient content,groundwater quality and slope stability.Soil macropores could provide a material basis for the occurrence of preferential flow,so that the water and solute could rapidly infiltrate into deep soil.Study on soil macropores and preferential flow characteristics in different types of land use can provide a theoretical basis for evaluating the effects of the preferential flow on the allocation of water resources and water resources utilization,meanwhile it can provide a scientific basis for regional water resources management,groundwater pollution assessment and the prevention of geological disasters,etc.This study combined the methods of CT scanning of soil columns and indoor dyeing tracer test and applied image analytics and mathematical statistics analysis to investigate the spatial structure of soil macropore and analyze the occurrence and development characteristics of preferential flow in the three typical land use types(grassland,garden,forest land)in northern Beijing.The main conclusions are summarized as follows:(1)Different morphology characteristics of soil macropores could be found in the three types of land use.The macropores of grassland soil are mainly tubular forms which have small relatively diameters,amounts and the strong connectivity.However,there are more macropores,dispersed distributions and relatively strong connectivity in the soil that are on the surface of gardens,while the amount of macropores in the deep soil is smaller than the soil in the surface.The three-dimensional structure of macropores in forest land soil is a form of cluster,which is composed of a large number of well-connected tubular paths.(2)The quantity and volume of macropores in different land use types were significantly different and showed a trend of that the forest land>the garden>the grassland.With the increase of soil depth in the three types of land use,the number and volume of macropores gradually decreased.In terms of the distribution of macropore diameter,the three types of land use have the same trend that the proportion of pores decreased with the increase of diameter range.(3)The dyed area all decreased gradually with the increasing of soil depth in grassland,garden land and forest land.Apparent preferential flow phenomena could be found in the soil of three types of land use.Meanwhile,the preferential flow occurred in forest land firstly,the second one is grassland and the last one is garden land.(4)When the form of flow changes from the matrix flow to the preferential flow,we could found the biggest variation in the soil of forest land and the smallest variation was in grassland.The coefficient of variation of dyed coverage ratio was used as the index of preferential flow evaluation,the result showed that the development level of preferential flow in the three types of land use is that the forest land>the garden>the grassland.Soil density,organic matter content,sand content and root length density of 0-5 mm can affect the formation of preferential flow significantly in the study area(P<0.05).