Objective Soil structural stability reflects soil’s ability to resist water erosion, which is closely related to the content of soil water-stable aggregates and their organic carbon content. In the context of land use changes, investigating the distribution characteristics of organic carbon in soil aggregates under different land use types and its impact on structural stability is crucial for preventing soil erosion and understanding the mechanisms of organic carbon sequestration. Moreover, purple soil, as the predominant soil type in the Three Gorges Reservoir area and influenced by its parent material, is characterized by shallow soil layers and poor, unstable structure, making it highly susceptible to soil erosion. However, the response of soil structural stability to the content of soil water-stable aggregates and their organic carbon content remains poorly understood in the Three Gorges Reservoir area.

Methods To investigate the distribution characteristics of organic carbon within soil aggregates and its impact on soil structural stability under different land use types in the purple soil region of the Three Gorges Reservoir area, six typical land use types within the Huangdunxi small watershed in Jiangjin district were selected. Vegetation characteristics and soil properties, along with water-stable aggregate content of different particle sizes and their organic carbon contents, were measured. Then, soil structural stability parameters, including soil structural stability index (SSI), mean weight diameter (MWD), and geometric mean diameter (GMD), were calculated. Differences in water-stable aggregates of different particle sizes and their organic carbon content, as well as soil structural stability under different land use types, were analyzed, and main controlling factors of the differences in soil structural stability were identified.

Results The results showed that water-stable aggregates of different particle sizes, their organic carbon contents, and soil structural stability differed significantly among different land use types. Except for slope farmland, the particle size distribution of water-stable aggregates for the other five land use types was dominated by aggregates > 0.25 mm, but the content of 5– > 2 mm aggregate was the minimum in all land use types. The organic carbon content across different water-stable aggregate sizes exhibited a unimodal distribution. It initially increased and then decreased with increasing aggregate size, reaching its minimum in aggregates ≤ 0.25 mm. The SSI followed the descending order: evergreen coniferous forest > evergreen broad-leaved forest > shrubland > grassland > economic fruit forest > slope farmland. The MWD and GMD decreased in the following order: shrubland > evergreen coniferous forest > evergreen broad-leaved forest > grassland > economic fruit forest > slope farmland. Overall, slope farmland exhibited the poorest soil structural stability, followed by economic fruit forest. Redundancy analysis revealed that variations in soil structural stability were significantly influenced by soil organic carbon, > 5 mm aggregates, silt content, organic carbon in 5– > 2 mm aggregates, 2– > 0.25 mm aggregates, and ≤ 0.25 mm aggregates. Among these factors, soil organic carbon and > 5 mm aggregate content were the main controlling factors, accounting for 56.11% and 17.28% of the variations, respectively.

Conclusions In conclusion, economic fruit forest and slope farmland remain potential sources of soil erosion in the Three Gorges Reservoir area. Given the rapid expansion of economic fruit forest along the rivers in the reservoir area in recent years, improving their soil structure and enhancing erosion resistance are crucial for controlling soil erosion and non-point source pollution loss in the reservoir area, which is vital for achieving green development in the Yangtze River Economic Belt.