How Is Overland Flow Sediment Transport Capacity Affected by Biological Crusts?

Abstract Overland flow sediment transport capacity () governs soil detachment and sediment deposition processes, yet its regulation by biological soil crusts (BSCs), particularly across varying algae–moss community compositions, remains poorly quantified. In this study, five BSC community compositions spanning an algal‐ to moss‐dominated gradient were selected on the Loess Plateau. was measured using a scouring flume under six slope–discharge combinations (10°–25° and 0.2–1.0 L·s −1 ). The results showed that ranged from 0.99 to 12.30 kg·m −1 ·s −1 and was reduced by 11.47%–23.07% relative to bare soil, with progressively greater reductions from algae‐dominated to moss‐dominated crusts. Among the measured BSC characteristics, surface roughness showed the strongest negative correlation with and accounted for the largest unique fraction of its variation (59%) in the variation‐partitioning analysis of BSC characteristics. The relative contributions of BSC characteristics and hydraulic parameters varied with increasing hydraulic forcing, suggesting a transition toward greater hydraulic influence near a shear stress of 10 Pa. Two empirical power‐law equations incorporating surface roughness and shear stress provided good fits to the observed under the lower‐ and higher‐shear‐stress conditions, respectively. These findings demonstrate that BSC‐induced changes in surface roughness govern sediment transport under shallow overland flow conditions and provide a mechanistic framework for improving erosion prediction and ecological restoration in semi‐arid regions.