| Soil erosion on the Loess Plateau of China is very serious both in China and in the world.Small watershed as an independent Erosion and Sediment yield unit plays an important role in the study of soil erosion.This study analyzed pattern variation of soil erosion in Liu Dao Gou catchment locating in the wind-water crisscross region of Shenmu County using composite fingerprinting technique.Soil samples were collected both in the catchment and in the dam field.Soil sampling in the catchment was based on variation o the land use type,landforms and soil type.Sediment in the dam field was collected by layers in the depostion profiles.The time series of sediment in the deposition profile of the dam was established depending on the local rainfall data,and major events records related to soil erosion.The potential fingerprint properties were selected from the physical and chemical properties of soil samples.We defined the sediment source using composite fingerprint identification,and estimated the deposition amount.The main research conclusions are as follows:(1)Since the dam was built in 1978,the check dam held the sediment about 74654 t,the soil erosion in the catchment was about 7319.19 t / km~2 · a,and the soil erosion intensity was extremely strong.According to the sediment deposition characteristics and the soil erosion intensity,the soil erosion in the small catchment is divided into three stages: the first stage was from 1978 to 1987,the soil erosion rate of the small catchment is 12144.93 t / km~2 · a,which belongs to the extreme soil erosion.The second stage was from 1988 to 1997,the soil erosion modulus is 14930.52 t / km~2 · a,which belongs to the extreme soil erosion.The third stage was from 2001 to 2013,the soil erosion modulus is 7907.14 t / km~2 · a,which belongs to the intensity soil erosion.Soil erosion in this study area is mainly dominated by gravity erosion.The main role of hydraulic erosion is the material that collapses on both sides of the channel due to gravity erosion.The gravity erosion of this study area is related to the special topography and geomorphology.On the other hand,it has a great relationship with the drastic disturbance in the area.There are many coal mines in the area,all of which are coal mined areas and mined areas Soil subsidence is also an important reason for the severe gravity erosion of soil in this area.(2)We divided the potential source land into five categories through on-the-spot investigation,they are: red mud gully wall,loess gully wall,sheet sand area,the abandoned farmland,the slope region.We found the optimum fingerprint through the Kruskal-Wallis H test,which consisted of Cr,Mg,Ba,Na,Y and TN(soil total nitrogen).These 6 fingerprint properties discriminated 91.7% of the sediment source samples correctly.In the potential sediment sources,the red mud gully had the largest contribution(79.7%),followed by the sheet sand region(12.9%),loess gully wall(5.4%)and the abandoned farmland(2.1%)contributed much less,while the slope region barely had no ersion at all.(3)We analyze the particle composition and the thickness of sediment layers in different locations of check dam.We found the increasing trend for the total thickness of sediment,the thickness of sand and clay layers,the mean grain size of sediment layers and the coarsening degree of the particle composition.Moreover,the and the sand bed’s coarsening degree of sand layers was larger than that of the clay layers.The sediment in different location of dam is mainly composed of the fine sand(59.77%),followed by silt(23.41%),clay particle(11.21%)and coarse sand(5.62%).Novel changes have taken place in the particle composition of sedimentary cycles,it provides a very good indicator for time scale determination using combined with precipitation,strong erosion events and topography of the catchment. |
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