Impact Of Detachment And Transport Of Rainfall Erosion On Sediment Organic Carbon

The influence of soil erosion process on soil organic carbon and global carbon cycle process is a hot topic and a difficult point in this field.However,the influence of the dynamic process of slope erosion on the characteristics of organic carbon loss is not clear at present.Based on the natural rainfall erosion event in field plot,this paper aimed at the change of sediment organic carbon and its composition and particle distribution characteristics during the separation and transport of rainfall erosion in the Loess Plateau,the evolution of rainfall erosion process in the Loess Plateau and the effects of runoff yield and sediment particle distribution on the characteristics of organic carbon loss on the slope were studied from the slope scale.The changes of organic carbon characteristics in splashing sediment,sheet erosion sediment and sediment transport from different distance were analyzed,and the relationship between sediment particle composition and organic carbon content and composition in sediment under different erosion processes was discussed.This paper attempted to reveal the mechanism of the influence of slope erosion separation and transport on the organic carbon content and its components in eroded surface and sediment.The main results of the study are as follows:(1)SOC>MOC>POC was observed in the erosive topsoil and erosion sediment.SOC and MOC content was the lowest under moderate rain intensity.SOC and MOC in splashing sediment of small rainfall intensity increased at first and then decreased with the increase of slope,while POC was the opposite.The content of organic carbon in eroded topsoil did not change obviously with slope,and the enrichment of SOC,MOC,POC in eroded topsoil and splashed sediment was consistent with the enrichment pattern of eroded soil particles.(2)The SOC,MOC,POC in eroded sediment decreased with the increase of slope under the condition of small rain intensity.Under the condition of moderate rain intensity,the SOC,MOC,POC increased at first and then decreased.Under the condition of heavy rain,SOC and MOC in eroded sediment decreased at first and then increased with the increase of slope,POC increased at first and then decreased.The variation pattern of DOC in runoff was consistent,when the rain intensity is relatively low,the DOC content showed an increasing trend in the fluctuation,with the increase of the rain intensity,it decreased rapidly at first and then increased slowly.The variation of DOC in runoff transport flux with rain intensity was characterized by bimodal distribution.When the rain intensity is small,theDOC transport flux increased slowly,and then decreased slowly with the increase of rain intensity.The regularity of SOC,MOC,POC enrichment in eroded topsoil and sediment was consistent with the enrichment pattern of eroded soil particles.(3)The change of SOC,POC and MOC content in the erosion sediment in different transport processes was consistent with the slope length.The content of SOC,POC and MOC decreased with the increase of the slope length and then increased slowly in the fluctuation.Among them,the organic carbon content of 5m slope length was the largest,and the mass concentration of DOC in runoff has no consistent variation with slope length.The variation characteristics of DOC transport flux with rain intensity increased at first and then decreased,under the same rain intensity,the DOC transport flux in runoff decreased at first and then increased slowly with the prolongation of slope length.The regularity of SOC,MOC,POC enrichment in eroded topsoil and sediment was consistent with the enrichment pattern of eroded soil particles.(4)There was little difference in organic carbon content in soil surface and sediment under different experimental conditions of the same component organic carbon.For SOC,the whole content of organic carbon showed as different transport distance > sheet erosion >uneroded topsoil and eroded topsoil > splash erosion.The variation of MOC content was largest in sheet erosion,followed by different transport distance,the content of MOC in uneroded topsoil,eroded topsoil and splash erosion were close and minimum.The overall change of POC was not obvious,but the SOC,MOC,POC content in splash erosion,sheet erosion and different transport processes was mainly affected by the sediment particle content before and after dispersion,and the amount of loss was positively correlated with the amount of erosion.The mass concentration of DOC in runoff during sheet erosion and different transport processes was mainly affected by slope,runoff,rainfall duration and E,the transport flux was controlled by runoff and rain intensity,respectively.