Geochemical Characteristics and Provenance Tracing of Surface Sediments in a Typical Agropastoral Ecotone: A Case Study from Kangbao Region, Northern China

Land desertification in the Agropastoral ecotone of arid and semi-arid regions poses significant threats to ecological security. Elucidating the geochemical characteristics and provenance of surface sediments is crucial for understanding desertification mechanisms and developing effective sand-control strategies. This study focuses on Kangbao County in the Bashang region of Hebei Province. We systematically collected 57 surface sediment samples from four geomorphic units: low mountains-hills, gently sloping hills, gully depressions, and undulating plains. Major and trace element concentrations were determined using X-ray fluorescence spectroscopy (XRF) and inductively coupled plasma mass spectrometry (ICP-MS). Elemental ratios, principal component analysis (PCA), and Non-metric Multidimensional Scaling (nMDS) were employed to decipher sediment geochemical signatures and provenance, emphasizing geomorphologically controlled source differentiation mechanisms. Key findings are as follows: (1) Geochemical characteristics reveal that sediment elemental enrichment or depletion patterns exhibit fundamental differences depending on the specific bedrock reference. When normalized against felsic versus mafic end-members, elements including Fe2O3, MgO, TiO2, CaO, Cr, Ni, Co, V, Rb, and Ba demonstrate contrasting geochemical behaviors. (2) The sediments originate from a homogenized mixture derived from the weathering of regional bedrock, clearly distinct from the high-maturity aeolian sands of the Hunshandake Sandy Land. (3) The spatial geochemical differentiation of surface sediments follows a two-stage process: the initial formation of a homogenized sediment source from bedrock weathering products, followed by subtle modification through landform-specific geomorphic processes, resulting in weak but systematic geochemical variations across the landscape. Based on these findings, a zonal management strategy is proposed to disrupt the localized sediment cycle by intercepting sources in hilly areas, restoring gully depressions, and blocking aeolian pathways on the plains. This study provides a scientific basis for precise desertification control in Kangbao and supports ecological barrier enhancement for the Beijing–Tianjin–Hebei region.