Contrasting sediment export despite similar hydrological responses in paired integrated crop-livestock watersheds

Purpose Runoff and sediment export are triggered by the same storms but need not scale proportionally across managed watersheds. We tested whether event-scale sediment export differed between two neighboring integrated crop-livestock watersheds after accounting for drainage area and the magnitude of runoff response under comparable rainfall forcing. Methods Three years of 10-min hydrometric and turbidity monitoring were evaluated for 58 contemporaneous rainfall-runoff events in two neighboring subtropical grain-dairy headwater watersheds (0.67 and 1.14 km²). Event discharge volumes were converted to runoff depths before watershed comparison. Paired Wilcoxon tests, rank-based rainfall-response analyses, a direct runoff-sediment analysis, and sediment-discharge hysteresis were used to compare responses. Turbidity-derived suspended sediment concentrations were interpreted with explicit attention to calibration uncertainty at high concentrations. Results After normalization by drainage area, total runoff depth, baseflow depth, surface runoff depth, specific peak discharge, and runoff coefficient did not differ significantly between watersheds. In contrast, maximum suspended sediment concentration and specific sediment yield were markedly greater in the north watershed ( p < 0.001), with maximum SSC reaching 25.6 g L − 1 versus 3.36 g L − 1 . Surface runoff depth was strongly associated with specific sediment yield within both watersheds (Spearman rho = 0.81 and 0.79), but a pooled log-transformed model showed a strong watershed offset ( p < 0.001), indicating substantially different sediment export at comparable runoff. Clockwise hysteresis predominated in both watersheds, whereas the hysteresis index did not differ significantly. Conclusion The results support partial event-scale decoupling in the magnitude of runoff and sediment responses: hydrological response was broadly similar after area normalization, whereas sediment export differed strongly between watersheds. Because drainage area, riparian condition, livestock access, tillage, soil composition, and other attributes co-varied, these contrasts are interpreted as system-level associations rather than isolated causal effects. Management should therefore address both runoff-generation pathways and sediment-transfer connectivity.