The effect of dynamic changes in vegetation coverage on the mechanism of organic carbon loss in inter-rill erosion

Abstract

The intricate effects of dynamic variations in vegetation coverage, representing different vegetation growth states and erosion conditions, on properties (content, enrichment and loss) of sediment and soil organic carbon (SOC) fraction in inter-rill erosion have not yet been fully elucidated. By setting micro-plots with different vegetation coverage ranges (0 %, 15 ∼ 35 %, 25 ∼ 55 % and 35 ∼ 70 %), the interaction mechanisms between vegetation coverage and inter-rill erosion, particle size distribution and SOC fractions properties during the vegetation growing period were studied. The average sediment yield, runoff yield and sediment concentration were highest under the bare plot, and diminished progressively with increased vegetation coverage. The effective clay content decreased with the increasing coverage, while ultimate clay was highest in the vegetation coverage range of 25 ∼ 55 %. Clay particle was transported as aggregates, with enrichment for all treatments except for the vegetation coverage range of 35 ∼ 70 %, providing transportation potential for SOC fractions loss. The content of SOC and mineral-associated organic carbon, as well as their enrichment ratio, decreased and then increased with coverage, which is the opposite of particulate organic carbon, and the loss of all fractions decreased with increasing vegetation coverage. Mineral-associated organic carbon dominated change in SOC, with proportion in SOC content and loss decreasing first and then increasing with vegetation coverage. The structural equation model showed the impact of vegetation coverage on SOC fraction loss was mainly achieved through indirect regulation of inter-rill erosion and particle size distribution. Our results provide new insights into the complex relationship between natural slope vegetation coverage and SOC loss, particularly from a fractions perspective, as well as understanding the ultimate fate of SOC in such environments.