Research On The Hydrological Characteristics Of Karst Underground Shallow Pores (cracks) Soil

The special ecological environment and the irrational utilization and development are the main reasons of the ecosystem degradation in the karst area of southwest China.Area soil formation rate is low,and because of the special surface/ground double space structure and hole shallow carbonate?crack?gap of the development of soil and water loss underground provides important migration pathway of karst region makes the way of slope soil erosion not only exists in the ground,and underground leakage occurs,will eventually,fissure filling pores in carbonate rocks.Although the formation of pore?fissure?gap provides a channel for underground leakage,on the other hand,the shallow layer of karst underground filled with soil provides a longitudinal space for the growth and development of vegetation and provides a positive impression for the restoration of ecological environment.Soil moisture in shallow pore?crack?gap in karst subsurface is one of the most important limiting factors of ecological environment in karst area,which determines the stability of ecosystem in this area.For the system to reveal the area of shallow underground fissure soil moisture migration regularity,characteristic and function of water conservation,infiltration mechanism,this paper,taking guizhou karst slope underground shallow hole?crack?gap as the research object,the experimental observations in the field,based on the analysis of the survey and indoor experiments,the karst underground shallow hole?crack?gap soil water-holding capacity,the moisture migration process and fissure study of soil porosity,the results of the study for the implementation of the national desertification recovery and ecological engineering and recovery provide scientific theory basis,the main results were as follows:?1?There are obvious differences among the soil properties of fissured soil under different vegetation types.Generally speaking,soil bulk density,total porosity and non capillary porosity of different vegetation types all increased with the deepening of soil layer,while non capillary porosity,saturated water content,field water capacity,capillary water capacity,root length density and root surface area density decreased with the depth of soil layer.Among them,the highest content of capillary water capacity is 37.63-56.46%for tree type,followed by shrub type>grassland type>cultivated land type;for field water capacity,the highest content is 35.20-52.15%for tree type,followed by shrub type>grassland type>cultivated land type.The content of soil organic matter in the surface layer?0-10cm?of fractured soil in cultivated land type is lower than that in the second layer?10-20cm?.In the soil aggregate,the content of air dried aggregate>0.25 mm is higher?91.99-98.61%?,but the water stable aggregate is only 71.60-90.24%.The damage rate of soil aggregate in the surface layer?0?10cm?of cultivated land is the highest among the four vegetation types?31.33%?.Under the four vegetation types,the clay?<0.002mm?of fissured soil increased with the deepening of soil layer,while the silt?0.002-0.02mm?and sand?0.02-2mm?decreased with the deepening of soil layer.The content of clay and sand is the highest in the four vegetation types,while the content of silt is the highest in the farmland type.The permeability coefficient of fissured soil decreased with the deepening of soil layer,and the four different vegetation types of fissured soil can be fitted with the logarithmic function y=aln?x?+b.?2?The results of field single ring infiltration of karst shallow fissure soil show that the infiltration rate of fissure soil shows a rapid decline stage and a stable stage,and the stable infiltration time of each fissure sample point is quite different.The stable infiltration time of fissure soil is concentrated in the period of 20-60min,and the fluctuation of infiltration process of fissure soil is mainly concentrated in the period of 0-10min.Compared with Kostiakov model and Philip model,Horton model has the best fitting applicability to the infiltration process of fissured soil?accounting for 8?,which can better simulate and predict the infiltration capacity and infiltration process of shallow fissured soil.Using Spearman correlation analysis,there was no significant correlation between permeability of fissured soil and root characteristics,bulk density,capillary porosity,total porosity and other factors?P>0.05?.At last,the main component equation P₁=0.243X₁+0.257X₂+0.267X₃+0.268X₄,which is obtained from the analysis of the infiltration capacity evaluation of fractured soil,is used to reveal that the order of infiltration capacity of karst shallow fractured soil from strong to weak is grassland>arable land>tree>shrub.?3?The change rule of dye area ratio in the vertical section of karst shallow fracture soil with fracture depth is that the dye area ratio decreases with the increase of soil depth,and the dye depth of each fracture sample point is different?23.00-74.60cm?.Among the soil factors,bulk density,non capillary porosity,total porosity and dye area ratio were significantly correlated?P<0.01?,clay content and dye area ratio were significantly correlated?P<0.05?,while capillary porosity,silt content,sand content and organic matter content were not significantly correlated with dye area ratio?P>0.05?.There was a significant correlation?P<0.01?between saturated hydraulic conductivity,maximum water holding capacity,capillary water holding capacity,field water holding capacity and effective water content.There was a significant correlation between root length density and dye area ratio?P<0.01?,and a significant correlation between root surface density and dye area ratio?P<0.05?.At last,the nine influencing factors that have significant correlation with the preferential flow of fissured soil are extracted for principal component analysis,and the nine influencing factors selected in the study are arranged as follows according to the comprehensive load value and the contribution rate of principal component:saturated water content,total porosity,bulk density,capillary water capacity,field water capacity and effective water content Volume,non capillary porosity,root length density,saturated hydraulic conductivity.