Identification of sediment sources and exploration of scale effects in the black soil region of Northeast China

Sediment provenance plays an important role in describing soil erosion characteristics and assessing the benefits of soil and water conservation measures. To further understand the transfer of sediment, a Bayesian mixing model-based fingerprint tracing technique was used in this study to quantify the relative contributions of sediment sources to the bottom of the gullies. Two catchments, the Hebei catchment with an area of 27.6 km² and its sub-catchment with an area of 3.5 km², located in the black soil region of Northeast China, were selected to identify sediments from cultivated topsoil, uncultivated topsoil, and gully soil. Seventy soil samples were collected from each catchment to characterize the sediment sources. Five sediment samples deposited in gully bottoms were collected from each catchment. Although a composite sampling method was applied, the spatial variability in the fingerprints between the Hebei catchment and its sub-catchment showed significant (p < 0.01) differences. The different optimum composite fingerprints obtained for the two catchments were: Ba, Ga, Br, Ce, and P for the Hebei catchment and Ba, Ga, Br, and As for its sub-catchment. In both catchments, over 95% of the sediment deposited in the gully bottoms was from cultivated topsoil and gully soil. However, the relative sediment contribution of cultivated topsoil and gully soil were significantly (p < 0.01) different between the two catchments. Notably, 42.0% and 47.8% of sediments were from cultivated topsoil while 55.3% and 49.6% of sediments were from gully soil (mean absolute fit > 0.95) in the Hebei catchment and its sub-catchment, respectively. Most of the sediment from the gully (>60%) was deposited in the upper segment of the gully bottom while the sediment from cultivated topsoil gradually increased in the lower segment.