Effect of soil erosion on dissolved organic carbon redistribution in subtropical red soil under rainfall simulation

Abstract

Water erosion governs soil carbon reserves and distribution across the watershed or ecosystem. The dynamics of dissolved organic carbon (DOC) under water erosion in red agricultural soil is not clear. To determine the effect of tillage management and water erosion on vertical and lateral transportation of soil organic carbon (SOC) and DOC production under distinct rainfall intensities in the hilly red soil region of southern China, a chisel tillage plot with low rainfall intensity (CT-L) and two no-tillage plots with high (NT-H) and low rainfall intensity (NT-L) studies were conducted. Soil samples were collected from 0–5, 5–10, 10–20, and 20–40cm soil layers from triplicate soil blocks pre- and post-rainfall for determining concentration of SOC and DOC. Runoff samples were collected at every 6min for determining concentration of DOC and sediments during rainfall simulations on runoff plots (2m×5m) with various intensities. No fertilizer was applied in any plots. Results clearly show that runoff volumes, sediments and SOC entrained with sediment, and laterally mobilized DOC were significantly larger on NT-H compared to other plots, coinciding with changes in rainfall intensity; and the extent of roughness of the plot surface (CT vs. NT) was the variation in runoff DOC concentration. During the simulated rainfall events, DOC exports average 0.76, 0.64, and 0.27gCm−2h−1; SOC exports average 3.52, 1.08, and 0.07gm−2h−1 in the NT-H, NT-L, and CT-L soils, respectively. The maximum export of DOC was obtained under a high intensity rainfall plot, which lagged behind maximum runoff volumes, sediments, and SOC losses with sediment. Export of DOC was proportional to SOC content of soil loss. The least DOC losses in surface runoff and SOC losses with sediment were observed in CT-L plots. Vertical DOC mobilization achieved its maximum with low intensity rainfall under CT treatment. The DOC did not accumulate at the soil surface and was distributed mainly in the second and third soil horizons. The distribution of DOC content down the soil profile increased compared to pre-rainfall, except for subplots E at NT-H and NT-L. Results indicate that rainfall significantly increased DOC content in experimental plots. The SOC content of sediment leaving the erosion zone was significantly correlated with overland flow volume and soil loss. These observations lead to the conclusion that soil erosion is an important factor controlling the export of dissolved organic carbon.