Spatial heterogeneity and drivers of soil inorganic carbon fractions in loess-derived croplands of the former Yellow River Delta

Soil inorganic carbon (SIC) is increasingly recognized as a dynamic component of the terrestrial carbon cycle, yet its behavior in humid and semi-humid loess croplands remains poorly understood. We quantified SIC and its lithogenic (LIC) and pedogenic (PIC) fractions across 20 soil profiles (0-100 cm) in croplands of the former Yellow River Delta (FYRD), a coastal loessderived landscape shaped by historic Yellow River migrations. SIC stocks were dominated by inherited LIC (2–8 g kg⁻¹), while PIC remained smaller (<4 g kg⁻¹) but spatially variable. LIC declined by more than 50% in the northern FYRD, coinciding with lower soil pH and reduced Ca²⁺ and Mg²⁺ availability, indicating enhanced dissolution under acidifying conditions. In contrast, PIC accumulation was more pronounced along the historic river route, where elevated pH (~8.0) and higher Ca²⁺ concentrations favored carbonate precipitation. These patterns demonstrate that SIC heterogeneity in FYRD loess croplands emerges from the interplay of soil alkalinity, cation supply, and geomorphic history. The results highlight that even in humid loess agroecosystems, traditionally viewed as SOC-dominated, SIC can undergo both depletion and formation. This work contributes to a growing body of evidence that SIC is sensitive to land use and management, and should be integrated into carbon accounting frameworks, especially in calcareous coastal agroecosystems undergoing rapid transformation.