The Characteristics Of Microtopography And Its Effect On Soil Moisture In The Loess Region Of Northern Shaanxi Province

The current artificial plantations on semi-arid loess slopes in northern Shaanxi is facing problems such as insufficient soil moisture and degraded forest land.Topographic heterogeneity can make redistribution of material and energy on the slope.Therefore,the use of habitat heterogeneity on the slope microtopography to provide theoretical guidance for artificial afforestation will improve the success of artificial afforestation.However,the study of soil moisture in micro-topography only stays in the difference in water characteristics between different micro-topographies.The mechanism of micro-topography that leads soil moisture variation and more detailed laws of soil moisture in micro-topography needs to be further study.This study was conducted through multivariate statistical analysis,time series analysis,and geostatistical analysis based on the soil moisture fixed point monitoring data and the three-dimensional scanning data of micro-topographies.The characteristics and distribution rules of 4 different microtopography on the loess plateau were clarified,and then the effect of microtopographic shape features on soil moisture was studied.Finally,the response laws of different microtopographic soil moisture to natural rainfall were obtained.The results shows that:1)The shape features of the four types of microtopography are not the same.The average area of the microtopography was sort as follow:platform>ephemeral gully>sinkhole>scarp;the fractal dimension index was sort as:scarp>ephemeral gully>platform>sinkhole,The length of uphill was sort as platform>sinkhole>scarp>ephemeral gully.Resluts indicating that the platform has the largest area among the 4 kinds of micro-topography,while the scarp has the most complex boundary,and the epgemeral gully is the closest to the top of the slope.(2)Site type not only affects the average area of micro-topography,but also affects the proportion of area occupied by micro-topography.In this study area,the area of micro-topography in gentle semi-shadow slope is the largest,with 19.89%,19.55%for gentle suny slopes,15.79%for gentle shandy slopes,14.75%for gentle semi-sunny slopes,12.49%for steep semi-sunny slopes and 10.78%for steep semi-shandy slope.Different micro-topography has different slope ratios in different site types,with scarp having the largest proportion in gentle shandy slopes,platforms having the largest proportion in semi-shandy slopes,and sinkhole occupying the largest proportion in semi-shade slopes,ephemeral gully has the largest proportion in gentle sunny slopes.This result can benifit for the near-natural vegetation afforestation planning.(3)At the end of the dry season,the soil water content in the four kinds of micro-topographes was sort as scarp<sinkhole<ephemeral gully<platform.However,the coefficient of variation of soil moisture on shandy slope was less sunny slopes indicating that despite the better soil moisture conditions in the previous studies,in the dry season,the soil moisture loss rate is higher.(4)Among the various topographic factors of microtopography,the area of microtopography has a significant effect on soil moisture content.Among them,on the shady slope,the soil moisture and microtopographic areas of the 4 kinds of microtopography both show an increasing trend.There is a linear function relationship between the micro-topography area and soil moisture for scrap,ephemeral gully and sinkhole,while logarithmic function relationship for platform.On the sunny slope,there is a positive logarithmic correlation between the area of the platform.The soil moisture of the scarp increases linearly with the area.The soil moisture of the ephemeral gully decreases linearly with the increase of the area.At the same time,the soil moisture within the micro-topography also has a significant distribution difference,which needs to be considered in the future vegetation allocation process.(5)Analysis of time series showed that in the study area,the autocorrelation of soil moisture was significantly different among the microtopography,and the soil moisture was greatly affected by the previous period moisture,and the time-dependent domain of the water series of the platform,sinkhole,and ephemeral gully was 4 weeks.The time-dependent domain of the scarp and the original slope is 2 weeks.The impact of precipitation on the deeper soil(120cm)is still a relatively slow process,and there are significant differences between the different micro-topography and the original slope surface.It takes 12 weeks for the platform,10 weeks for the sinkhole,18 weeks for the scarp,6 weeks for ephemeral gully and 12 weeks for the original slope.The recharge time of precipitation to relatively deep soil is an important reason that leads to different soil moisture condition among micro-topographies.