| The ecological protection and high-quality development of the Yellow River basin are important contents of the construction of ecological civilization in the new era in China.The exposed feldspathic sandstone region is one of the main coarse sand source regions in the middle reach of Yellow River.Studying the regulatory mechanism of artificial vegetation on hydraulic erosion had great significance to guide vegetation construction and reduce coarse sand into Yellow River.Small watershed of Baojiagou in the exposed feldspathic sandstone region was selected as the research object in this thesis.The law of erosion sediment yield,micro-topographic change process and hydrodynamics characteristic of slope of the exposed arsenic sandstone area were clarified clearly by monitoring runoff plot and wild drainage washout test in the slope;the impact of rainfall and vegetation on runoff and sediment production of slope were analyzed;flow-reduction and sediment-reduction mechanism of artificial vegetation were studied with the main artificial vegetation in exposed feldspathic sandstone region from the aspects of multi-layer system of rainfall holding back,physical property of soil and hydrology,santi-erodibility and soil quality,and the minimized data set for evaluating soil quality of the exposed feldspathic sandstone region was established.Geographic information database was constructed based on the research of basic soil characteristics,data related to topography,land usage and vegetational cover of the area from the watershed scale.Then the impact of artificial vegetation layout and topography on spatial heterogeneity of soil quality was researched by combining with the theory and method of geostatistics.The vegetation layout of small watershed and the law of spatial variation of hydraulic erosion were analyzed by using the theory of landscape ecology and special analysis method,to reveal the coupling impact and action mechanism of vegetation layout and topography factors on hydraulic erosion.The main research results were showed as follows:(1)The rainfall types in the research area are divided into four categories:long-duration heavy rain,long-duration moderate to heavy rain,short-duration heavy rain,short-duration light to moderate rain.Rainfall can significantly change micro-topography of slope of exposed bed rock,which has no impact on the slope where there is vegetation growing.During the rainstorm season,the average value of micro-topographic slope of exposed bed rock slope increases from 22.76°to 23.09°,the density of gully of rill on the slope surface increases from 0 to 33.73 m/m2.With the development of microtopography of slope surface towards the direction in favor of occurrence of erosion persistently,the quantity of flow yield and sediment yield on the slope surface increase.As the number of washout flow rate and slope increases,the scouring capability of runoff and the runoff and sediment production along with it becomes more and more.Low vegetational cover(≤15%)has relatively small impact on slope runoff,and erosion sediment yield is easily to occur by hydraulic scour;while when vegetational cover reaches 30%,its block action on runoff increases evidently,weakening the washout capacity of runoff.(2)There are difference in surface coverage under different vegetation types,The highest value of surface coverage in Hippophae rhamnoides and Pinus tabuliformis,it was 1.41 and 1.26 times that of the grassland.The interception ability for different vegetation types followed the order of Pinus tabuliformis>Prunus armeniaca>Caragana korshinskii>Hippophae rhamnoides>grass land;We also found that Water holding capacity of litter according to vegetational factors a trend:valley floor>slope>ridge;The occurrence macropore of in the soil has a very important role in the soil saturation conductivity,and soil of bare land exhibit low porosity,soil saturation conductivity;The highest value of soil infiltration rate in Hippophae rhamnoides,the others were Pinus tabuliformis,Caragana korshinskii,Prunus armeniaca,grass land and bare land.(3)The damage mechanism of rainfall on soil aggregates in exposed soft sandstone area is different.The gas explosion caused by heavy rain is the main factor that leads to the destruction of soil aggregates in exposed soft sandstone area,dispersion of the raindrops was followed by the destruction,and the destruction of soil structure due to water absorption expansion the least.Hippophae rhamnoides exhibited the lowest soil aggregate processing damage rate,followed by Pinus tabuliformis,Prunus armeniaca,Hippophae rhamnoides,Caragana korshinskii,Hippophae rhamnoides grass land and bare land.At first,soil physical nutrient,biochemical functions and antierodibility properties were analyzed.Afterwards,we employed PCA(principal component analysis)and MDS(Minimum data set)to establish an indices system of soil qulity.The minimum data set(MDS)for soil quality assessment of artificial forest in the Feldspathic sandstone region should encompass the following eight indices,that is soil organic matter conten,soil moisture content and soil aggregate processing damage rate.The calculation shows that the calculations of MDS was very satisfied with calculations of SDS and TDS.The soil quality evaluation showed a rank from best to the worst as Hippophae rhamnoides,Prunus armeniaca,Caragana korshinskii,Pinus tabulaeformis,grass land and bare land.(4)Baojiagou small watershed is the most typical watershed among Feldspathic sandstone region.The dominant landscape in the basin is exposed bedrock landscape,followed by a large area of artificial vegetation landscape.The intensity of hydraulic erosion in the Baojiagou watershed is mainly micro-erosion,which is the main erosion landscape in the watershed.The degree of fragmentation of each erosion intensity patches ranged from large to small in the order of extremely strong erosion,strong erosion,moderate erosion,mild erosion and micro erosion.There is a significant spatial autocorrelation of the hydraulic erosion intensity in the watershed.The high-value accumulation area of the hydraulic erosion intensity is mainly located in the area where the bedrock is exposed largely,and the formation of the high-value accumulation area is closely related to the slope.The low-value aggregation area is mainly distributed on the slope,and the degree of aggregation is related to the degree of plaque fragmentation.Terrain is the main factor that leads to the fragmentation of vegetation landscape and determines the intensity of hydraulic erosion.In the gentle terrain,the connectivity of vegetation landscape is the main factor restricting the development of hydraulic erosion. |
