| The karst trough valley area not only has the above-ground /underground binary space structure,but also has the typical geological structure of the along/reverse strata.It is very easy to cause soil erosion during rainfall,which makes the karst trough alley area an ecologically fragile area.Due to the difficulty of monitoring soil erosion/loss in the karst trough area,the process and mechanism of the soil erosion/loss in the arst trough area are still unclear,so it is impossible to make more reasonable and efficient measures to prevent soil erosion.In this experiment,under the conditions of field vestigation of Longtan trough valley,the method of artificially simulating the rainfall process was used to design the rainfall intensity to be 30mm/h,60mm/h,90mm/h.The overlapping area of the holes is used to simulate the crack degree of underground holes(1%,2%,3%,4%,5%),and then to study the characteristics of runoff,sand and nitrogen and phosphorus loss in the karst trough area,with a view to the production of karst trough area A scientific basis for the disclosure of abortion and the mechanism of nitrogen and phosphorus loss.The results show:(1)Rain intensity has no obvious effect on the concentration of total nitrogen,ammonium nitrogen,and nitrate nitrogen,but has an effect on the concentration of total phosphorus and water-soluble total phosphorus,which decreases with the increase of rain intensity.The total nitrogen concentration in surface runoff is the highest under the condition of 90mm/h rain intensity on the surface and underground runoff,and the concentration of ammonium nitrogen and nitrate nitrogen is the ighest under the condition of 60mm/h rain intensity on the surface and underground runoff.The concentrations of phosphorus and water-soluble total phosphorus are the highest in the surface and underground runoff under the 30mm/h rain intensity kit.Under different rainfall conditions,the nitrogen concentration is that the underground runoff is higher than the surface runoff,and the phosphorus concentration is that the surface runoff is higher than the underground runoff.The rock formation inclination mainly affects the distribution of nitrogen and phosphorus on the surface and underground,that is,under different rock formation inclination,the nitrogen concentration is higher in the underground runoff than the surface runoff,and the phosphorus concentration is higher in the surface runoff than the underground runoff.Under different rock layer inclination conditions,the concentrations of total phosphorus,ammonium nitrogen,nitrate nitrogen,total phosphorus,and water-soluble total phosphorus are higher in the reverse layer slope than the bare layer and the bedding layer slope.(2)The greater the rainfall intensity,the greater the above-ground and above-ground production flow in the karst trough area.Under the condition of light rain intensity(30 mm/h),the underground flow rate is greater than the surface flow rate;under moderate rain intensity(60 mm/h)and heavy rain level(90 mm/h),the bare slope flow rate is equal to the surface and underground surface flow The flow rate is generally greater than the underground flow rate,and the bedding slope and reverse layer slope show that the surface flow rate is less than the underground flow rate.The greater the underground pore fissure degree,the greater the distribution ratio of underground runoff.The 2% underground pore fissure degree is the critical value of the bedding slope underground runoff greater than the surface runoff,and the reverse layer when the underground pore fissure degree is greater than 3% The slope has no surface runoff.(3)Under the condition of bedding slope,the greater the rock layer inclination,the surface flow and distribution ratio will increase first and then decrease,and the underground flow and distribution ratio will increase;under the reverse layer slope condition,the rock formation inclination angle is 90 The surface production flow is the largest at °,the surface production flow is the smallest at 60 °,and the underground production flow is the largest at the rock formation inclination angle of60 ° and the smallest at 90 °.Under the condition of bedding slope,the rainfall intensity has the greatest influence on the surface underground runoff among the factors,followed by the crack degree of underground holes.Under the reverse layer slope condition,the rainfall intensity has the greatest influence on the surface runoff,followed by the rock layer dip angle;among the factors that affect the underground runoff,the rainfall intensity has the highest impact,followed by the underground pore fissure degree.(4)Under bedding slope conditions,the greater the rain intensity,the greater the surface underground production flow.The rain intensity has a significant impact on the total nitrogen,ammonium,and nitrate nitrogen losses on the surface,and the phosphorus loss is mainly affected by heavy rain(90mm/h).Rain intensity mainly affects the amount of sand produced on the surface.Under the condition of medium and small rain intensity(30mm/h ~ 60mm/h),it has a greater impact on nitrate nitrogen.Under reverse slope conditions,the greater the rainfall intensity,the greater the surface underground production flow,and the rainfall intensity increases significantly the total and ammonium nitrogen and nitrate nitrogen losses on thesurface and underground.The rain intensity mainly affects the surface sediment yield,and the heavy rain intensity(90mm/h)has a greater impact on the underground sediment yield.As the rain intensity increases,the loss of nitrate nitrogen in the sediment also increases.(5)Under the condition of bedding slope,with the increase of rock pore fissure degree,the surface runoff will decrease.Under the condition of 3% porosity,the amount of nitrogen and phosphorus loss in runoff is the largest,and under the condition of bedding slope,phosphorus in runoff The loss occurs mainly through the1% porosity condition,while the nitrogen loss occurs mainly through the 3% porosity,and the surface sediment mainly occurs through the 1% and 3% pore fissures.Under reverse slope conditions,surface runoff decreases with increasing pore fissure degree,and underground runoff increases with increasing pore fissure degree.Total nitrogen,nitrate nitrogen,total phosphorus and water-soluble total phosphorus are mainly lost through 1% ~ 2% pore fissure degree.With the increase of the pore fissure degree,the surface sediment production shows a decreasing trend,while the underground sediment production shows an increasing trend.With the increase of pore fissure degree,the change relationship of nitrogen and phosphorus loss in sediment is not obvious,indicating that the underground fissure degree has little effect on the loss of nitrogen and phosphorus in runoff. |
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