Study On The Change Of Organic Carbon In Slope Erosion Sediment Under Different Conditions

Soil erosion is the main driving factor of the dynamic change of soil carbon pool and the main link that affects the global carbon cycle.Due to the complexity and variability of slope soil erosion,different erosion conditions(erosion mode,cover condition,scale and rainfall characteristics,etc.)have different effects on the characteristic parameters of organic carbon(content,component and enrichment)of eroded sediment.However,most of the existing studies focus on certain specific conditions,and lack of comparative studies under different conditions,which limits the in-depth understanding of the mechanism of slope organic carbon loss and the variation of characteristic parameters of organic carbon in sediment erosion.In this paper,the typical loess soil was taken as the research object,and the plots with different slope erosion conditions were set up to measure the organic carbon and component content,loss amount and enrichment ratio of eroded sediment in each plot under natural rainfall,and compared with the uneroded soil.Splash erosion under different conditions are analyzed,the sheet erosion and the erosion of the mixture(rill and groove)between organic carbon content in the sediment,erosion and change characteristics of enrichment ratio,explore ways erosion,covering conditions(different aperture iron net and vegetation coverage),slope length and rainfall characteristic parameters influence on erosion and sediment organic carbon characteristic parameters,This paper attempts to reveal the variation mechanism of characteristic parameters of organic carbon in slope erosion sediment under different conditions.The main conclusions are as follows:(1)The spatter amount increased significantly with the increase of average rainfall intensity(P<0.01);The average content of organic carbon(SOC)and mineral-bound organic carbon(MOC)in splashed sediment was slightly higher than that in uneroded soil,and relatively enriched,while the average content of granular organic carbon(POC)was lower than that in uneroded soil,and relatively depleted.The change of rainfall characteristics had no obvious effect on the change of organic carbon and its components.With the increase of spatter erosion amount,POC content of spatter erosion sediment increases,while SOC and MOC contents decrease.The organic carbon and component of spattering migration were significantly correlated with average rain intensity(P<0.05),and increased with the increase of average rain intensity.Organic carbon migration of each component was significantly correlated with spatter amount(P<0.01),and organic carbon loss of each component increased with the increase of spatter amount,and MOC migration was greater than POC.(2)Under different mesh size(1 mm,2.5 mm,5 mm,1 cm,2 cm),erosion plot is smaller than bare slope,and it increases with the increase of mesh size.Compared with bare slope,the contents of SOC and MOC were higher than those of POC under different mesh sizes except 2 cm diameter.With the increase of mesh size,the contents of SOC and MOC increase,while POC decreases.The loss of SOC,POC and MOC of bare slope was significantly higher than that of grid pore size(except 5 mm pore size),and the loss increased with the increase of grid pore size,and the loss of organic carbon was MOC>POC.The SOC enrichment ratio of bare slope erosion sediment is higher than 1 mm and 2.5 mm pore size,but lower than 5 mm,1 cm and 2 cm pore size.The SOC enrichment ratio increases with the increase of mesh size.The POC enrichment ratio in bare slope sediment is lower than that under mesh aperture coverage,and the POC enrichment ratio in 5 mm aperture is the highest.The ENRICHMENT ratio of MOC increases with the increase of mesh aperture,and the enrichment ratio of 1 mm and 2.5 mm is lower than 1,while the enrichment ratio of MOC is greater than 1 under other conditions.The influence of sediment yield on organic carbon is greater than that of runoff,and the loss of MOC is greater than that of POC.(3)The increase of vegetation coverage significantly reduced sediment yield and changed the relationship between runoff yield and sediment yield.The regulation effect of vegetation coverage on sediment yield was stronger than that on runoff.The SOC,POC and MOC contents in erosion sediment under different vegetation coverage were not significantly different from those in bare slope,and there was no obvious change rule or enrichment phenomenon.The loss of SOC,POC and MOC in bare slope erosion was significantly higher than that in vegetation coverage,and decreased with the increase of vegetation coverage.The main rainfall factors affecting organic carbon and its components,loss,enrichment ratio,POC/SOC and MOC/SOC were different between bare slope and different vegetation coverage.POC,MOC,SOC loss and sediment yield are positively correlated linearly,and positively correlated with sediment yield is greater than that of sediment yield.(4)The runoff per unit area decreased with the increase of slope length and increased with the increase of rainfall intensity,and the 5 m slope length was significantly higher than other slope lengths.Sediment erosion per unit area fluctuates with the slope length,and increases with the increase of rainfall intensity and energy.The sediment erosion per unit area is the largest under the slope length of 14 m,and there is no significant difference among different slope lengths.The average POC content of eroded sediment was the highest in 20 m slope length and the lowest in 17 m slope length,and there was no significant difference in POC content under different slope lengths,but it was basically lower than that of uneroded soil.The average contents of MOC and SOC were the highest under 5 m slope length,and the lowest under 11 m slope length.The enrichment ratio of organic carbon and its components showed a similar trend to its content.POC loss was the highest under 14 m slope length and the lowest under 5 m slope length,and there was no significant difference among different slope lengths.The variation trend of MOC and SOC loss was consistent,with the highest value at 17 m slope length and the lowest value at 5 m slope length,and there was no significant difference at each slope length.The correlation between the loss of organic carbon and its components and rainfall parameters showed that when the slope length was 11 m and 17 m,there was no correlation between the loss of POC and rainfall parameters,and when the slope length was 8,11 and 17 m,there was no correlation between the loss of MOC and SOC and rainfall parameters.In other cases,organic carbon loss of each component was significantly correlated with rainfall parameters.Runoff yield and erosion have significant effects on SOC,MOC and POC losses under different slope lengths.(5)Under different erosion modes,SOC content of sediment is splash erosion > chip erosion > mixed erosion(rill and rill),POC content is splash erosion > splash erosion > mixed erosion,MOC content is splash erosion > chip erosion ≈ mixed erosion,indicating that POC content is more sensitive to chip erosion,while MOC content is more sensitive to splash erosion.The amount of splashed sediment is the main factor affecting the carbon content and the migration of organic carbon flow,while the rainfall factor has an indirect effect,and the impact of rainfall factor on the migration of carbon component is greater than the impact of splashed sediment.Sheet erosion and erosion process,the mixed terrain factors had the greatest influence on the carbon content in the erosion and sediment,followed by rainfall factor,measures factor and slope erosion and sediment yield in the(),all is given priority to with immediate effect,including terrain factor,measures factor and slope erosion characteristics for the negative effects,and the rainfall factor is positive effect,indirect effect for the negative effects of the rainfall factor,The effect of direct positive effect on carbon content in sediment erosion was weakened.Slope erosion has the greatest influence on organic carbon loss,followed by topography,rainfall and measures,all of which are positive effects.The direct effects of slope erosion characteristics and measures were the main factors,while the indirect effects of topographic factors and rainfall factors were the main factors through changing slope erosion characteristics.