The Effects Of Vegetation Structure On Runoff And Sediment Yield In The Diediegou Watershed Of Liupan Mountains Of China,Ningxia

The vegetation structure played key roles on runoff and sediment yield caused by rainfall.However,the quantitative relationship between vegetation structure and runoff and the quantitative relationship between vegetation structure and erosion is not yet clear.In this study,runoff yield and sediment yield under natural rainfall events and artificial rainfall events were observed under typical vegetation and simulated vegetation with different vegetation structures were observed in the small watershed of Diediegou in Liupan Mountain in Ningxia Hui Autonomous Region.Then the effects of different vegetation and different vegetation layers?herb layer and litter layer?on runoff yield and sediment yield were compared and quantitatively analyzed,in order to provide a theoretical basis for formulating effective soil and water conservation measures and the management strategy of water conservation forest.The main conclusions are as followings:?1?In the Diediegou watershed,the monthly variation of precipitation in the small watershed of Diediegou showed a very obvious single-peak pattern,with rainfall concentrated from July to September.The precipitation was dominated by light rain with low intensity and low rainfall.?2?Under the low rainfall intensity condition(1.17?12.86 mm·h^-1),i.e.,the natural rainfall,stored-full runoff was the main pattern of runoff yield,with runoff coefficient of 0?0.46%.Runoff and sediment yield varied with vegetation type,slope gradient and slope aspect;the greater the slope gradient was,the greater the runoff and sediment yield were,e.g,the runoff yield and sediment yield from Larix principis-rupprechtii plantation on steep slope was greater than that of Larix principis-rupprechtii plantation on gentle slope;the closer it was to the shady slope,the greater the runof yield was,e.g,the runoff yield of grassland on semi-sunny slope was greater than that grassland on sunny slope,but the slope aspect had little effect on the sediment yield.Forest age had little effect on runoff and sediment yield.?3?Due to the influence of vegetation type,slope gradient and slope aspect,the runoff yield exhibited the following order in the Diediegou small watershed:Hippophae rhamnoides scrubland on semi-sunny slope>grassland on semi-sunny slope>Larix principis-rupprechtii plantation on steep slope>grassland on sunny slope>Larix principis-rupprechtii plantation on gentle slope.The sediment yield exhibited the following order:Larix principis-rupprechtii plantation on steep slope>Hippophae rhamnoides scrubland on semi-sunny slope>grassland on sunny slope>grassland on semi-sunny slope>Larix principis-rupprechtii plantation on gentle slope.?4?Surface cover?grass layer coverage,litter thickness?and previous soil water content significantly affect the runoff and sediment yield of a single rainfall.The runoff coefficient and soil erosion rate of Larix principis-rupprechtii forest,Hippophae rhamnoides shrub,and natural grassland all decrease rapidly and then slowly with the increase of herb layer coverage and litter thickness.After comparison,this study uses an exponential equation to simulate The effect is better.However,due to the influence of early soil moisture content,as the thickness of litter increases,the change in runoff coefficient fluctuates,mainly because the increase in soil moisture content in the early stage will increase the runoff coefficient;and with the increase of litter thickness,soil erosion rate slowing shrieking.