Objective Identifying sediment sources in check dam-controlled watersheds is essential for understanding soil erosion and sediment transport processes and for formulating soil and water conservation measures.

Methods This study took the Wanshenglong check dam in the Ten Tributaries as the research object, with forestland, grassland, cropland, and bare land selected as potential sediment source areas. A composite fingerprinting technique was applied to quantitatively analyze the sources of deposited sediment.

Results Fe₂O₃, P, and low-frequency mass-specific magnetic susceptibility (χ_lf) were identified as the optimal fingerprint factor combination. Its classification accuracy reached 83.3%, and the mean goodness-of-fit (GOF) was 0.89, indicating reliable model performance. Bare land contributed the largest proportion of the sediment (76.89%; unit-area yield ratio, 4.05), followed by cropland (14.80%; unit-area yield ratio, 14.51). Forestland (5.41%; unit-area yield ratio, 5.30) and grassland (2.90%; unit-area yield ratio, 0.04) had lower contributions. Further analysis across sedimentary cycles revealed that extreme precipitation events increased sediment layer thickness and coarsened sediment particle size. The contribution of forestland rose, suggesting that its soil and water conservation function may be weakened under extreme rainfall.

Conclusions Bare land and cropland are the main sediment sources in the watershed, with bare land contributing the most overall and cropland having the highest unit-area yield. Forestland and grassland play a positive role in soil and water conservation, indicating that cropland-to-forest conversion and grassland restoration are of great significance for strengthening the soil and water conservation capacity of the watershed. Under the background of potentially more frequent extreme precipitation, greater attention should be paid to the soil and water conservation functions of forestland to enhance the system's resilience to disturbance.