| In order to explore the variability of soil erodibility and its influencing factors in different erosion fields during surface and underground erosion in karst fault basin in eastern Yunnan.Based on the hypothesis that vegetation restoration can reduce soil erodibility by changing soil nutrient status and soil aggregate stability,this paper sets up sample plots in the surface and underground erosion process of Haifeng karst basin in eastern Yunnan,collects soil samples and analyzes soil physical and chemical properties.Based on soil aggregates,the erodibility of surface and underground erosion fields in karst fault basin is comprehensively evaluated by index weight analysis,and the following conclusions are drawn:(1)The physical and chemical properties of soil in karst fault basin have obvious vertical variability and spatial heterogeneity.In the process of surface erosion,different vegetation types and process of underground leakage,soil organic carbon(SOC),total nitrogen(TN),total phosphorus(TP),>5mm aggregate,>0.25 mm aggregate,average weight diameter of soil aggregates(MWD),geometric average diameter of soil aggregates(GMD),soil structure stability index(SSSI)and comprehensive soil nutrient index(CSNI)decreased with the increase of soil depth.Therefore,the stability of soil structure decreases with the increase of soil depth,and the comprehensive soil erodibility index(CSEI)increased with the increase of soil depth.The stability of surface soil structure is better than that of deep soil structure.SSSI(0.97,0.64 and 0.50)and CSNI(0.77,0.57 and 0.65)in the process of surface erosion,different vegetation types and process of underground leakage belong to strong variability.The CSEI(0.15,0.15)of surface erosion process and different vegetation types belong to moderate variability,while the CSEI(0.05)in the process of underground leakage belongs to weak variability.(2)Vegetation restoration is beneficial to promote the accumulation of soil nutrients and the formation of large soil aggregates,thus enhancing the stability of soil aggregates and reducing soil erodibility.Among different vegetation types,SOC,TN,MWD,GMD,SSSI and CSNI of Castanopsis orthacantha and Lithocarpus dealbatus primary forest and Myrsine africanan shrub are higher than those of Pinus yunnanensis forest.Among the three kinds of Pinus yunnanensis forests,SOC,TN,MWD,GMD,SSSI and CSNI of artificial mixed forest are the highest,followed by natural secondary forest and the artificial pure forest is the lowest.Therefore,the soil erodibility of Castanopsis orthacantha and Lithocarpus dealbatus primary forest(0.37-0.53)and Myrsine africanan shrub(0.44-0.55)is lower than that of Pinus yunnanensis forest.In Pinus yunnanensis forest,the soil erodibility of artificial mixed forest is the lowest(0.44-0.58),followed by natural secondary forest(0.52-0.59)and the soil erodibility of artificial pure forest is the highes(0.56-0.65).Vegetation restoration is beneficial to enhance soil stability and reduce soil erodibility.(3)The soil erodibility of each erosion field in karst fault basin is significantly different,which increases with the erosion process.The soil erodibility in the process of underground leakage is higher than that in the surface erosion process,and there is a risk of secondary erosion.Soil erodibility is closely related to soil physical and chemical properties.The MWD,GMD,SSSI and CSNI in the process of underground leakage are lower than those in the process of surface erosion.Therefore,the CSEI of underground leakage process(0.56-0.72)is higher than that of surface erosion process(0.36-0.69),and there is a risk of secondary erosion.In the process of surface erosion,the soil erodibility of slope is lower than that of lowland,with the lowest soil erodibility at the middle slope(p<0.05)and the highest soil erodibility at the foot of slope(p>0.05).In the process of underground leakage,the soil erodibility of karst caves is lower than that of fissure,sinkholes and underground rivers.In the two fissures,the soil erodibility of Pinus yunnanensis secondary forest fissure is significantly lower than that of Myrsine africanan shrub fissure(p<0.05).In the sinkholes,the soil erodibility of the bottom(D6)is the highest,followed by the south cave wall(D5),and the north cave wall(D4)is the lowest.North cave wall is significantly different from bottom and south cave wall(p<0.05).SOC,TN,organic carbon cementation index(SCAI),aggregates > 5mm,GMD and MWD are the main influencing factors of soil erodibility.It shows that higher soil SOC,TN,>5mm aggregates content and better soil aggregate stability can effectively reduce soil erodibility.(4)By comparing the comprehensive evaluation method of soil erodibility in karst fault basin with the K value of this study area and other karst landform types,it is found that the comprehensive evaluation method of soil erodibility is applicable to the evaluation of soil erodibility in karst fault basin.In the process of surface erosion,the soil erodibility K value is between0.108-0.208,the soil erodibility at the middle slope is the lowest,and the soil erodibility at the foot of slope is the highest.With the progress of erosion and the increase of soil depth,the soil erodibility shows an upward trend.Under different vegetation types,the K value is 0.173-0.273,and the K value of Pinus yunnanensis forest is higher than that of Castanopsis orthacantha and Lithocarpus dealbatus primary forest and Myrsine africanan shrub.Among the three Pinus yunnanensis forest,the soil erodibility of artificial mixed forest is the lowest,followed by natural secondary forest,and the soil erodibility of artificial pure forest is the highest,and the soil erodibility increases with the increase of soil depth.It is consistent with the conclusion of comprehensive evaluation method of soil erodibility.The CSEI of Haifeng karst fault basin is between 0.36 and 0.72,and the soil erodibility is at a higher level,which is consistent with the previous research conclusions. |
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