| The karst peak cluster depression area is one of the eight large karst landform types in southwestern China.It is mainly distributed in the central and western parts of Guangxi.It is characterized by less mountains and more land.When rainfall occurs,the rain carries sediment directly through the vertical cracks on the slope.The underground space causes the soil on the slope to "leak more and less",but "less leaks".However,different from non-karst areas,soil leakage is the most important ecological and environmental geological problem in the karst peak cluster depression area,making it the highest type of rocky desertification and the landform type area of national key governance.Therefore,it is necessary to carry out research on soil leakage on slopes in karst peak cluster depression area.This paper takes Guangxi Guohua demonstration area as a typical case,through monitored rainfall,epikarst spring,soil water,slope farmland runoff plot and slope surface runoff plot,as well as tested the physical and chemical properties of soil samples,particle size,agglomerates,isotopes and organic matter at different slope positions,in order to research the characteristics,influencing factors,processes and prevention of soil leakage on slopes.The main achievements were as follows:(1)In 2018,the total rainfall in study area was 1531.7mm,mainly concentrated in the flood season from May to October,accounting for 83.6%of the annual rainfall;the non-flood season was centralized in two periods,January to April and November to December.There were 407 times of rainfall during the year and the number of rainy days during the year was 154 days.The erosive rainfall was the premise of soil leakage.The rainfall distribution in the study area was extremely uneven during the year,resulting in concentrated rainfall in July to September,while rainfall erosivity was the largest in September,followed by July and August,almost had no erosion in February and November.Rainfall erosivity was significantly positively correlated with monthly rainfall and erosive rainfall.(2)There are significant differences in the physical and chemical properties of the soil at each point profile of the slope in the karst peak cluster depression area,and the degree of soil leakage is different.Compared with the other three points,the soil sample at P4 had the higher characteristics of water content,larger porosity and larger surface aggregates,and the fractal dimension was small,so the possibility of leakage was small,which indicated that the bamboo forest land had better soil and water conservation capacity and corrosion resistance.The soil particle size at each point was mainly composed of powder particles,followed by clay particles,and the sand content was the lowest.The fractal dimension of each point was basically the same as the change trend of clay with soil layer;the content of organic matter decreased with the increase of soil depth,and the content of surface organic matter was the highest;the 137Cs was mainly distributed within 20cm and discontinuous distribution below 20cm.(3)Due to the accumulation of soil or soil leakage,the clay of the sample will decrease with the increase of soil layer,and the soil organic matter will suddenly increase at the bottom of the soil layer,and the 137Cs below 20cm will show a sharp increase or decrease trend.According to the correlation analysis of the data,there were no significant correlation between 137Cs and large than 0.25mm of aggregates;it was negatively correlated with clay,while at the point of soil leakage,137Cs was significantly negatively correlated with clay;it was positively correlated with soil organic matter,indicating their changes in the soil are similar,and soil organic matter can be used to study the process of soil leakage.It was also possible to use the 137Cs in the fractured soil and the external environment to study soil leakage characteristics of the slope,and to quantify soil leakage through epikarst and soil water.As Buyangyihao epikarst the relationship between flow and rainfall was obvious,and had a certain hysteresis,the lag period was about 2h.The greater the rain intensity of 30 min,the larger the leakage of Buyangyihao epikarst.(4)The conceptual process model of soil leakage in karst peak cluster depression geomorphology was constructed and divided into four processes:? rainfall erosion;? surface erosion on slope surface,the leakage of epikarst and underground pore fissure;? leakage of silt shafts,funnels and sinkholes;? underground space movement The annual soil erosion of the slope was estimated,and the ratio of surface soil erosion to underground soil leakage was 1:2.The main particulate matter in soil water was clay,and at medium rainfall intensity,the possibility of soil leakage was greater.Under a series of ecological environment control measures,the research area had significantly reduced the degree of rocky desertification and soil erosion/leakage.(5)It can be seen from the monitoring experiment of slope farmland runoff plot whatever surface soil erosion or rock cracks leakage,the water and soil conservation effect of crop intercropping was significantly better than that of single crops.Pitaya+pasture had the best effect in preventing soil erosion/leakage,followed by pitaya+eyebrows and pitaya+peanuts;pitaya and eyebrows had better soil erosion/leakage conservation effects than corn and peanuts.It can be seen from the slope runoff plot prevention test that the effect of crop soil and water conservation was:jelly fruit>pitaya>cattle>corn.Therefore,the prevention and control measures for soil leakage on slopes in the karst peak cluster depression area are proposed:the prevention and control of local slopes should be carried out for different slopes,and the combination of biological measures and engineering measures should be emphasized. |
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