Where does the eroded sediment from hillslopes go in small karst watersheds?

Abstract

The transport mechanisms of eroded sediment in watersheds have long been a focal point and challenge in the field of eco-hydrology, especially in the context of increasingly frequent extreme climate events globally. However, few studies have focused on the hillslope to watershed scale eroded sediment transport mechanism in karst areas. This study analyzes long-term changes in hillslope eroded sediment yield (ES) and catchment suspended sediment yield (SS) using long-term in-situ hydrological and sediment observation data from two typical small karst watersheds (Huyangshui (HYS) and Yangjichong (YJC). The cross-scale sediment delivery ratio (SDR) from slope to watershed was also estimated. Combined with karst hydrological theory and observed characteristics, this study reveals the cross-scale transport mechanisms of eroded sediment in these karst watersheds. The results indicated that the hillslope ES was significantly higher than the catchment SS in both karst watersheds ( p < 0.05). Their temporal trends during the respective observation periods were complex. Specifically, HYS small watershed exhibited a non-significant increasing trend in ES and a significant increasing trend in SS; YJC small watershed showed a non-significant increasing trend in ES and a non-significant decreasing trend in SS. The average SDR was low in both watersheds, 0.183 for HYS and 0.173 for YJC. Mechanistically, the low SDR in karst areas stems from the region's distinctive “surface-subterranean” dual hydrogeological structure. During transport, this structure forces eroded sediment through a dual-process of surface retention and subsurface leakage-deposition, which drastically reduces the proportion of sediment that ultimately reaches and is measured at the catchment outlet. This study systematically reveals the sediment transport mechanisms in small karst watersheds, thereby enriching the theory of sediment dynamics in karst areas and thus laying a theoretical foundation for the targeted precision control of soil and water loss in similar regions.

The authors' abstract, as published at the source. CATENA, 2026 · DOI ↗