Erosion-deposition processes drive soil organic carbon mineralization through aggregate breakdown and buildup

Water erosion critically influences lateral soil organic carbon (SOC) redistribution and CO₂ emissions in terrestrial ecosystems. While SOC redistribution patterns have been extensively studied, the mechanisms by which erosion–deposition regulates SOC mineralization via aggregate turnover (breakdown and buildup) remain unclear. This study integrated rare earth oxides tracing, 30-minute flume experiments for simulate erosion–deposition, and 56-day soil incubation for monitor aggregate turnover over time to investigate soil aggregate turnover-mediated SOC mineralization. Cumulative aggregate breakdown (CBD) and buildup (CBU) rates were significantly higher in soils from the erosional area (SE) (CBD: 10.49 %; CBU: 13.26 %) than in those from the depositional area (SD) (9.55 % and 9.83 %, respectively), indicating more intense aggregate dynamics in SE. Both erosion and deposition enhanced SOC mineralization, showing a descending order: SE (41.39 mg kg⁻¹) > SD (30.37 mg kg⁻¹) > control (CK) (24.21 mg kg⁻¹). The kinetic model y = K(1-e^-bx) (R² > 0.90) effectively described SOC mineralization dynamics, with parameters K and K·b indicating greater SOC mineralization potential in SE than in SD and CK. Structural equation modeling identified aggregate breakdown as the primary driver of mineralization, with a much higher path coefficient in SE (0.703) than in SD (0.110). In contrast, aggregate buildup suppressed mineralization via physical protection, with a stronger effect in SD (path coefficient: 0.334) than in SE (0.215). These results confirm that aggregate breakdown is a key regulator of SOC dynamics during erosion–deposition, providing critical insights for carbon management. We propose implementing watershed-scale engineering structures (e.g., check dams, gully stabilization systems, and sediment retention basins) to create depositional zones, which can reduce SOC loss and mitigate CO₂ emissions, thereby enhancing SOC sequestration.