Soil And Water Leaking Characteristics In Karst Depressions And Its Prevention And Control Technology Test

On a global scale,soil erosion is a problem of ecological imbalance,especially in the karst area with dual structure of surface and underground,the co-existence of surface surface soil erosion and leakage of Water and Soil,it is directly large areas of bedrock exposed,aggravated the degree of rocky desertification,has an important impact on agricultural production activities.Therefore,this paper selects the Longlie desertification control demonstration zone depression type of Pingguo county as the research object,By monitoring the relationship between the annual precipitation in2018 and the runoff and sediment concentration in ponor,detected the soil physical properties and isotope ¹³⁷Cs,and built the runoff plot in the depression to test the effect of soil erosion conservation,to provides theoretical basis and practical experience for the study of soil erosion and treatment in karst depression.The results have showed that:?1?There are two main ways leakage of soil and water in karst depressions:surface erosion in depressions?the ponor leak?underground river;Underground fissure leakage in the depression?underground river.The ponor is an important channel for water and soil leakage.Monitoring shows that when the rainfall reaches the intensity of moderate rain,rainstorm and downpour,the rainfall has obvious influence on the flow rate of the ponor,while the impact of light rain is small.Precipitationis positively correlated with flow.At 11 o'clock on September 18,2018,there was a guilt in the depression,and the depth of the inner sac was about 200 cm.The peak value of sediment concentration is about 30min-90min behind the peak flow rate.The turbidity of the falling water hole is positively correlated with the sediment content.The linear equation is y=801.33x+1.7833,and the coefficient of determination R²=0.5627.It is proved that the determination of sediment concentration by turbidity is feasible.The amount of soil deposited by the sedimentation pond of the Luoshui Cave for one year was calculated to be 49.73442t/?km²·a?.?2?The total precipitation in the study area was 1531.81mm in 2018,was mainly concentrated May-October,accounting for 83.5%of the annual recipitation.The maximum recipitation occurred in September,reaching 19.67%,and the minimum appeared in November,only 0.85%.There are clear boundaries between the rainy season and the dry season in the study area,and the difference between the two seasons is about 5 times.The months with the most rainy days were July and August,and the months with the least rainy days were February.The average daily rainfall for each month was 10.04mm in September only 0.47 mm,and the difference between the two was about 21 times.In 2018,there were 154 days of rain,mainly light rain,followed by moderate rain,followed by heavy rain and rainstorm.Heavy rainstorm occurred once.?3?The erosion intensity in 2018 was mainly from June to October,and the maximum rainfall erosivity was on September 18,reaching 1238.83MJ·mm/?hm²·h?.The daily rainfall erosivity is 50-100mj·mm/?hm²·h?,which accounts for 50%,and accounts for 25%above 200MJ·mm/?hm²·h?.The maximum monthly rainfall erosivityappeared in September,reaching 2335.60MJ·mm/?hm²·h?,and the minimum was November,only 14.05MJ·mm/?hm²·h?.?4?According to the statistical analysis of soil-water stable aggregates,all the large soil-water stable aggregates are greater than 75%.The larger proportion of the aggregate it was indicated that the better the water stability of the plots.The proportion of water-stable large agglomeration in the surface soil?0-5 cm?maximum appeared at W4,and the minimum appeared at W1.W4 soil water-stable aggregates MWD and GMD are larger than other sampling sites,,indicated that W4 soil aggregates had the best effect.?5?The soil mass loss in the karst depression was proved by the ¹³⁷Cs mass activity of the profile.For example,in the W2 area,the mass activity at 45-50cm¹³⁷Cs also showed a higher value.The correlation between soil aggregates,clays,organic matter and ¹³⁷Cs was used to analyze the water and soil loss.The results show that the correlation between the mass activity of ¹³⁷Cs and the large aggregates larger than0.25mm is only 0.3453,indicating the mass distribution of ¹³⁷Cs.The activity has little effect,soil aggregates can not be used to prove the phenomenon of water and soil loss;the ¹³⁷Cs mass activity has good correlation with clay and organic matter,except for the W2 profile.The possible reason is that there is a large amount of soil loss in the area,which broken this rule.?6?It can be known from the soil and water conservation effects of different land use modes in the test area that the total surface runoff generated by different land use modes is different,runoff plots generated runoff size order for pitaya interplanting Erythropalum scandens>pitaya interplanting Beautiful Millettia Root>pitaya interplanting Wintercreeper>pitaya interplanting peanut>pitaya interplanting soybean.The order of soil erosion and sediment yield was pitaya interplanting Beautiful Millettia Roo>pitaya interplanting Erythropalum scandens>pitaya interplanting Wintercreeper>pitaya interplanting peanut>pitaya interplanting soybean.The soil and water conservation effect of pitaya interplanting soybean was better than other four interplanting methods.