Research On Soil Erosion Effect Of Slope Cover Pattern In Loess Hilly And Gully Area

The soil erosion in the Loess Hilly Region is very serious because of its broken terrain,low vegetation coverage,frequent heavy rainfalls,and poor soil anti-erodibility.In the arid and semi-arid areas,in particular,vegetation restoration and construction are restricted by water conditions.Therefore,soil and water conservation is difficult to reach the ideal state.In this case,it becomes particularly urgent to rationally allocate the vegetation pattern within the carrying capacity of water resources in this area.In view of the serious soil erosion in the Loess Plateau,the optimization of land vegetative cover should proceed from the benefit of runoff and sediment reduction.In this way,the soil erosion effect of different land cover patterns should be studied;the scientific land cover pattern should be arranged appropriately;and at the same time,the index system for characterizing the soil erosion effect of different land-cover should be constructed.In this paper,firstly,the physical-chemical properties,infiltration properties and anti-scouribility of the soil under different land-cover factors were systematically studied and compared.And the spatial heterogeneity of slope soil formed by vegetation restoration and crustal growth was discussed.Secondly,the runoff and sediment erosion of different land cover patterns were discussed through simulated erosion experiments in the field in view of the different land cover pattern of hill slope caused by the spatial heterogeneity of slope soil.After that,for the reason that the qualitative description of slope land cover patterns is too simple to represent all the characteristics of it,the conditions and recommended index for using different pattern metrics to characterize slope land cover pattern are discussed.Finally,the effectiveness of applying pattern metric to represent land cover patterns and soil erosion is showed.The main conclusions are as the following:(1)During the process of vegetation restoration and succession in the Loess Hilly Region,the slope soil will get spatial heterogeneity due to their different ground conditions.With the vegetation restoration and crustal growth,the soil organic matter and water stable aggregates increase significantly,and soil bulk density decreases significantly.The infiltration performance and anti-scouribility of soil will increase through vegetation restoration;while the former will decrease and the latter will decrease because of crustal growth.In this way,the increase of soil organic matter and water stable aggregates was positively correlated with its anti-scouribility,which is negatively correlated with soil bulk density.The anti-scouribility of the soil under the canopy of Artemisiagmelinii community and the soil with crustal growth is respectively 3.22 times and 1.56 times that of the bare soil.And the infiltration performance of these two kinds of soil is 1.21 times and 0.841 times that of the bare soil respectively.(2)The different land cover pattern of slope all have benefits of runoff and sediment reduction,which is highly correlated with the coverage area directly.That means,the greater the vegetation coverage is,the more effective the runoff and sediment reduction is.Compared with the whole bared soil,the sediment reduction efficiency of the aggregation pattern on the top-slope,middle-slope,base-slope and the whole slope is respectively 43.75%,50.51%,48.84%and 71.04%of their measured efficiency.If the area of the land-cover is not to be counted,i.e.,the pattern of this cover is the only factor to be taken into consideration,the sediment reduction benefit of the middle-slope aggregation is relatively greatest.Besides,the effect of different land cover patterns is not identical due to their different soil erosion agency.And the sediment yield will increase with the increase of soil erosion agency.However,this result may not be achieved if the soil erosion agency further increases.(3)In order to study the effect of the land cover patterns,this paper classifies the 18 kinds of pattern metrics by means of statistical factor analysis.When the proportions of the patches significantly change,the five indexes of Percentage of Landscape(PLAND),Related Circumscribing Circle mean(CIRCLE_MN),Clumpiness(CLUMPY),Splitting Index(SPLIT)and Normalized Landscape Shape Index(NLSI)were relatively independent of each other,and their information is not so redundant,which could comprehensively describe the pattern information.And when the proportions of these patches are similar,the five indexes of PLAND,CLUMPY,NLSI,Fractal Dimension Index mean(FRAC_MN)and Effective Mesh Size(MESH)can fully describe the pattern information.On the whole,the indexes of PLAND,Related Circumscribing Circle mean(CIRCLE_MN),CLUMPY,SPLIT,NLSI,CLUMPY and MESH in the analysis of pattern can represent the pattern information comprehensively with less redundant information.(4)In the analysis of the question "Whether the pattern metric can reflect the soil erosion process",the pattern metrics and the representative variables of soil erosion are negatively correlated when it comes to the two landscapes of“source”and“sink”.And it is effective in the respective of type to use land cover pattern metrics to explain the differences of soil erosion.Moreover,the index of MESH and SPLIT are more effective than other indexes in indicating the soil erosion and sediment yield of landscape pattern.However,there is still uncertainty in indicating soil erosion through pattern metric because of the complexity of soil erosion and the limit of pattern metric though the index is effective in the respective of type.The land cover pattern is relatively stable within a certain period;while its erosion force changes a lot with the criticality.Therefore,only though analyzing the factors of erosion force can we achieve a better understanding of the soil erosion process.