Runoff processes and lateral transport of soil total carbon induced by water erosion in the hilly region of southern China under rainstorm conditions

Soil erosion by water destroys the physical protection of carbon in soil aggregates and accelerates decomposition, thus impacting soil organic carbon stocks and making the soil barren. Runoff process and lateral transport of soil total carbon were studied using sloping flumes in an artificial rainfall simulator. The flumes were filled with soil collected from the surface horizon, the underlying laterite horizon, and the deeper sand horizon, three portions of a weathered granite soil profile. The results showed that the initial runoff-yielding time was faster under large rainfall intensities and steep slope gradients. The runoff process on sand soil slopes showed a trend of increasing with the increase of rainfall duration, while the trend on surface soil slopes and laterite soil slopes were mainly increasing rapidly and then stable. The volume of overland flow on surface soil slopes was the largest under the same conditions, with an average value of 14,259 mL, while it was the smallest on sand soil slopes. There was no interflow on surface soil slopes, and the interflow curves of the sandy soil slopes and the laterite soil slopes were all single-peak curves. The TC concentration curves of overland flow on sand soil slopes presented a high initial concentration and were then decreasing to a stable state, but the trends on laterite soil slopes and surface soil slopes was not obvious. The TC concentration curves of interflow on sand soil slopes and laterite soil slopes were similar to those of the runoff process curves, and the TC concentration on laterite soil slopes peaked faster. The TC loss gross amount on sand soil slopes and laterite soil slopes was much larger than that on surface soil slopes. Sediment was the main carrier of TC on sandy soil slopes, which TC loss with sediment was more than 50% in each rainfall test. Runoff was the main carrier of TC on laterite soil slopes and surface soil slopes; TC loss with runoff was above 60% on surface soil slopes. At the same time, partial correlation coefficients showed that rainfall intensity was the most important factor affecting TC loss. The results can provide a calculation method and scientific basis for the estimation of the TC loss on weathered granite soil slopes in the south of China.