The Effect Of Interrill Erosion Process On Organic Carbon Loss Characteristics On Loess Slope

Soil erosion leads to a large loss of surface soil rich in organic carbon,which threatens soil resources,human survival and sustainable development.At present,the research on the influence of soil erosion on the loss of organic carbon mainly focuses on the content,enrichment characteristics,loss and its influencing factors of organic carbon in sediment,while the research is rarely involved on the corresponding analysis of different components of organic carbon in sediment,loss characteristics of different components,particle size sorting and slope erosion characteristic parameters in different erosion processes.Interrill erosion is the main process of slope soil erosion,and organic carbon is basically lost with sediment as the carrier under the condition of interrill erosion.However,due to the differences in the physical and chemical properties of organic carbon components and their occurrence modes in soil particles,the responses of organic carbon components to the process of interrill erosion may be different.Therefore,it is essential to systematically study the organic carbon content,component change,loss characteristics and influencing factors of erosion sediment in the process of interrill erosion to fully understand the influence of soil erosion on organic carbon loss.In this study,Yangling soil on the Loess Plateau was used as the experimental soil,and five rainfall intensities(42,60,90,120 and 150mm/h)and five slope gradients(7,10,15,20 and 25°)were used to investigate the loss characteristics of organic carbon in different components of slope surface,the content of organic carbon in sediment and the change of sediment particle size components during the interrill erosion process.The relationship between erosion parameters and sediment particle size components and the loss characteristics of organic carbon of different components was analyzed under different conditions,and the influencing factors of interrill erosion process on the loss characteristics of organic carbon in slope surface were revealed.To provide research ideas and theoretical basis for building slope organic carbon loss model.The main conclusions of this paper are as follows:(1)Rainfall intensity and slope gradient significantly affect the process and characteristics of slope erosion.Runoff rate,erosion rate and sediment concentration increased with the increase of rainfall intensity.There is a critical slope for the flow rate with the increase of slope,and the change trend on both sides of the critical value is opposite.Overall,the influence of rainfall intensity on slope erosion parameters is greater than that of slope.With the increase of rainfall duration,the runoff rate increases first,and then maintains a dynamic and stable state until the end of rainfall.On the contrary,erosion rate and sediment concentration decreased first and then stabilized with the increase of rainfall duration.(2)The silt fraction of effective particle size and absolute particle size of erosion sediment and original soil was the highest.The clay fraction of effective particle size in erosion sediment did not enrich,and the silt fraction and sand fraction enriched.In the absolute particle size composition,the clay and silt fraction are enriched,and the sand fraction does not enrich.It shows that fine particles are usually lost in the form of microaggregates during interrill erosion.By comparing the enrichment rate and aggregation ratio of effective particles composed of effective particle size and absolute particle size in erosion sediment,it was found that the clay particle size and sand particle size were more likely to be transported in the form of aggregate,while the silt particle size was more likely to be transported in the mixture form of single particle and aggregate.In the effective particle size composition,the clay particle size and sand particle size have a strong sensitive to rainfall intensity and slope gradient.(3)Slope gradient and rainfall intensity significantly affected the organic carbon content and loss rate of erosion sediment.Compared with the original soil,the total organic carbon and readily oxidized organic carbon content of erosion sediment were higher than those of the original soil,and the content of readily oxidized organic carbon in sediment was lower than that of the original soil in some experiments.With the increase of rainfall intensity and slope gradient,the contents of total organic carbon and readily oxidized organic carbon in sediment increased first and then decreased,and the content of hardly oxidized organic carbon decreased first and then increased.The loss rate of different components of organic carbon in the process of interrill erosion was large at the initial flow rate,and then gradually decreased,finally remained stable.The loss of organic carbon components increased with the increase of rainfall intensity and slope,but the influence of rainfall intensity on the loss of organic carbon was greater than that of slope.In addition,the enrichment ratio of total organic carbon and hardly oxidized organic carbon decreased exponentially with the increase of rainfall duration,while the readily oxidized organic carbon fluctuated during rainfall.(4)The flow rate,erosion rate and sediment concentration were significantly correlated with the content and loss rate of each component of sediment organic carbon(p < 0.05).There was no significant correlation between total organic carbon content and particle size fractions of effective particle size composition and absolute particle size composition.The content of readily oxidized organic carbon was only negatively correlated with the particle size fraction of effective particle size composition,and positively correlated with the sand particle size fraction of effective particle size composition.The content of hardly oxidized organic carbon was positively correlated with effective particle size and absolute particle size.There was a significant positive correlation between the organic carbon loss rate of different components and the effective and absolute particle size of silt,and a negative correlation between the organic carbon loss rate of different components and the clay particle size of the absolute particle size.The sand particle size of the effective particle size was negatively correlated with the loss rate of readily oxidized organic carbon and hardly oxidized organic carbon,and had no significant correlation with the total organic carbon loss rate.(5)Based on the structural equation model,the effects of slope gradient,rainfall intensity,sediment yield and particle size composition on the organic carbon content and loss rate of eroded sediment were analyzed.The results showed that the rainfall intensity had the greatest impact on the organic carbon content of eroded sediment,but the slope erosion characteristic parameters had the greatest impact on the organic carbon loss rate.In addition,the effect of rainfall intensity on total organic carbon content was mainly indirect effect,and the slope was mainly direct effect.The effect of rainfall intensity and slope on the organic carbon content of each component was mainly direct effect,but the effect of rainfall intensity and slope on the organic carbon loss rate was mainly indirect effect.