| Soil erosion is one of the serious environmental problems in our country, it could cause serious soil erosion, result in soil nutrients loss, decline land productivity, and severely damage land resources. In addition, soil erosion caused soil organic carbon(SOC) loss, which impacted on the SOC sequestration and regional carbon cycle, and thereby affected global climate change. Severe water erosion happened in hilly red soil region of southern China, and the study on SOC migration and redistribution caused by water erosion is a hot issue. In this study, field rainfall simulation experiments were carried out in the plot of 2 m(width) × 5 m(length). Rainfall events were performed on four chisel tillage plots with rainfall intensities of 100, 80, 40 and 30 mm/h and two no tillage plots with rainfall intensities of 80 and 30 mm/h, respectively, in order to analyze loss characteristics of runoff, sediment, SOC and mutual relations among them under erosion, and the differences in the SOC distribution before and after rainfall, which can explore the impact of water erosion on SOC migration and redistribution. In the meanwhile, SOC loss process was simulated by combining sediment transport model with SOC loss calculation theory.The results show that SOC in surface soil occurs horizontal redistribution after the simulated rainfall. SOC content decreases in the middle of the plot and increases in the bottom of the plot. At the same time, water erosion changes vertical redistribution of SOC. Vertical migration of SOC happens after a ll the rainfalls in the different slope positions. SOC contents decrease in the 0~20 cm and increase in the 20-40 cm. The results indicate that SOC is transported vertically from the surface 10 cm soil to the deeper soil layer under water erosion. Rainfall intensities and tillage methods have effect on SOC redistribution. Higher rainfall intensity and plough result in stronger redistributon.The loss process of sediment-dissolved organic C was similar to that of runoff except for the peak values appeared during 10~30 min in high-intensity rainfalls, and the sediment-bounded organic C loss rate firstly rose and subsequently kept a relatively stable value. The results above-mentioned demonstrated magnitude of runoff affected SOC loss; Loss process of runoff had an obvious effect on that of sediment-bounded organic C, but was not such obvious correlation with that of runoff-dissolved organic C. A positive linear relationship between SOC loss rate and runoff rate was shown. The regression analysis reveals variab ility of runoff can explain 80% of the variance in SOC loss, and runoff rate had a larger effect on sediment-bounded organic C than runoff-dissolved organic C. Cubic fitting is obtained between sediment-bounded organic C between and sediment loss. In addition to high rainfall for plowing tillage and low intensity rainfall for no tillage, significant correlations are observed between the both. The relationships between the amount of sediment-bounded organic C and sediment loss are significantly linear.The model of SOC loss could be effectively adapted to the simulation of SOC loss in hilly red soil region of central Hunan province during a rainfall event and get a wonderful simulation goodness and accuracy. The mean error from the simulation of SOC loss rate was observed to be around 30% with the detemination coefficient beyond 0.85 in CT and NT. In the meantime, the simulated results indicated the process of the sediment and SOC loss appeared fluctuant state under overland flow erosion. The sediment and SOC loss rate were rising at the first stage of 0~10 min after runoff began and then kept a relatively stable tendency. Comparing the model of sediment transport by runoff and SOC loss in NT with that in CT, results demonstrated that the sediment and SOC loss rate in CT were grater than that in NT under erosive rainfall. And the situation of sediment and SOC loss in CT kept similar to that in NT under non-erosive rainfall. |
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