The Role of Road and Ditch-Pond Networks in Regulating Sediment Connectivity: An Analysis of the “Source-Pathway” Relationship of Sediment in Subtropical Red Soil Hilly Watersheds from an Erosion-Connectivity Coupling Perspective

 Accurately identifying critical soil erosion source zones and sediment transport pathways within watersheds represents a key challenge in current soil erosion control and watershed management. To address this challenge, an integrated "RUSLE-IC" analytical framework was developed in this study, coupling the Revised Universal Soil Loss Equation (RUSLE) with an improved Sediment Connectivity Index (IC) to systematically quantify the spatial correspondence between erosion and transport processes. In this study, we utilized high-resolution UAV remote sensing techniques in a typical red soil hilly watershed in southern China. Based on calculated soil erosion modulus, and the sediment connectivity index was revised by integrating topography, vegetation, and road-ditch-pond artificial network elements. Additionally, the four-quadrant method was utilized to analyze the spatial matching patterns between erosion modulus and connectivity levels, thus accurately identifying the critical “source-pathway-sink” zones for sediment transport within the watershed. The results indicated that: (1) The predominant soil erosion level in the watershed was slight (75.43%), but the light erosion level, which accounted for only 23.50% of the area, contributed 60.03% of the total soil loss in the watershed, demonstrating highly spatially concentrated erosion. (2) The IC was significantly enhanced by the effects of road and ditch-pond networks, which combined to contribute 58.82% of the total IC enhancement effect. Meanwhile, a distance-threshold decay in the effect was observed, where the IC values decreased significantly with increasing distance within a 40-meter buffer zone (R²>0.91), but the effect weakened beyond that range. (3) The coupled erosion-connectivity analysis revealed that high erosion–high connectivity (HE-HC) zones, which comprising only 6.34% of the watershed area, contributed 25.76% of sediment yield and were identified as priority areas for management. And low erosion–high connectivity (LE-HC) zones (11.81%), predominantly associated with roads, ditches, and ponds, were characterized as potential high-efficiency sediment delivery pathways. Generally, (4) sediment transport in small watersheds was more sensitive to soil erosion source areas than to high-connectivity zones. The effectiveness of the proposed framework for identifying soil erosion and sediment delivery hotspots under complex surface conditions was validated, providing a scientific basis for implementing targeted soil and water conservation measures based on coordinated regulation of “source areas and transport pathways.”