Study Of Shallow Landslide Characteristics And Its Effects On Soil,Water And Carbon And Nitrogen Loss On Loess Grass Slope

Since the large-scale implementation of the National Project of Returning Farmland to Forest and Grassland,the vegetation construction on the Loess Plateau has achieved remarkable achievements,the vegetation cover has been well improved,and hydraulic erosion has been effectively controlled.However,under the condition of prolonged rainfall or rainstorm,the slope surface fully soaked by rainwater will still trigger landslides in the gully region of the Loess Plateau,causing gully weir blockage and road obstruction,posing a threat to regional agricultural production and ecological environment.Current studies on loess landslides focus more on the exploration of the genetic mechanism of landslides on exposed slopes,but the characteristics of shallow landslides on vegetated slopes and the rules of runoff and sediment transport,carbon and nitrogen loss under landslide disturbance are still unclear.Therefore,the characteristics and causes of shallow landslides as well as the effects of shallow landslides on sediment production and carbon and nitrogen loss on 35～40slopes under 1.0 mm/min rainfall intensity were studied in this paper by using the field simulated rainfall experiment to establish bare plot and grass plot.The aim of this study was to deepen the understanding of the erosion of shallow landslide on vegetation slope and provide scientific reference for the prevention and control of shallow landslide on vegetation slope in loess area.The main research results are as follows :(1)The rainfall-induced shallow landslide was caused by soil saturation.The depth of landslide on bare slope was higher than that on grassy slope,and the existence of root reduced the depth of sliding surface.Under the continuous seepage action of rainfall,the soil volume water content and pore water pressure in the landslide area developed from the lower slope to the middle slope and the upper slope.With the increase of soil volume water content and pore water pressure,the slope body gradually reached to the saturation state.Roots formed different soil environments between the upper and lower layers of the landslide surface,resulting in a lower soil bulk density and a higher total porosity and saturated water conductivity in the upper layer of the landslide surface.As the infiltration water filled the root soil space,the saturated layer of the root soil would slide along the landslide surface.(2)Landslide affected the processes of slope runoff and infiltration,inhibited rainfall infiltration and promoted slope runoff.Runoff rate varies with rainfall duration showed a linear increasing trend before landslide,and showed a power or quadratic changing trend after landslide.The average runoff rate after landslide increased by 125.0%～1357.6%compared with before landslide.Infiltration rate varies with rainfall duration showed a linear decreasing trend before landslide,and showed a quadratic changing trend after landslide.The average infiltration rate after landslide decreased by 55.7%～90.0% compared with before landslide.Water reduction efficiency of grass cover plants decreased after landslide.(3)Landslide affected the process of slope sediment yield,which significantly increased slope erosion,and changed the relationship between slope runoff and sediment.Sediment yield rate varies with rainfall duration showed a power increasing trend before landslide and an exponential changing trend after landslide.The average sediment yield rate after landslide increased by 7.18～899.00 times compared with before landslide.Sediment reduction efficiency of grass cover plants decreased after landslide.Correlation analysis between runoff rate and sediment yield rate showed that the correlation before landslide was stronger than after landslide.The cumulative sediment yield increased linearly or power function with the cumulative runoff volume and cumulative infiltration volume,and the response rate of sediment yield to runoff volume after landslide was higher than before landslide.(4)Landslide caused the redistribution of organic carbon,reduced the sediment organic carbon content,increased the risk of organic carbon loss,and affected the response of organic carbon loss to runoff and sediment.The average sediment organic carbon content after landslide was 23.6%～62.6% lower than before landslide.The average organic carbon loss rates in runoff and sediment after landslide were 0.95～10.60 times and 6.18～189.14 times higher than before landslide,respectively.Correlation analysis between organic carbon loss and runoff sediment showed that the correlation before landslide was stronger than after landslide.Regression analysis between organic carbon loss and runoff sediment showed that the landslide had little effect on the response relation.After landslide disturbance,the reduction rate of grass cover to organic carbon loss was reduced.(5)Landslide drove the migration of water,sediment and total nitrogen,changed the total nitrogen content in runoff and sediment,increased the risk of total nitrogen loss,and affected the relationship between total nitrogen loss and runoff sediment.The average runoff total nitrogen content after landslide was 3.0%～52.1% higher than before landslide,while the average sediment total nitrogen content was 16.5%～54.3% lower than before landslide.The average loss rates of total nitrogen in runoff and sediment after landslide were 1.20～9.29 times and 6.60～228.17 times higher than before landslide,respectively.Correlation analysis between total nitrogen loss and runoff sediment showed that the correlation before landslide was stronger than after landslide.Regression analysis between total nitrogen loss and runoff sediment showed that the landslide did not change the response relation,but it significantly increased the soil erosion loss.After landslide disturbance,the reduction rate of grass cover to total nitrogen loss was reduced.