Carbon accumulation in the red clay layer of the subsoil in a major river delta: Contribution of secondary carbonate
2020
Li, Yuan | Fu, Chuancheng | Zeng, Lin | Zhou, Qian | Zhang, Haibo | Du, Zhen | Wei, Jing | Li, Lianzhen | Luo, Yongming
Understanding C formation and budgets in soils of large river deltas is necessary in studying the global C cycle because deltas are important interfaces between continents and oceans for material fluxes. Soil organic carbon (SOC) and soil inorganic carbon (SIC) were assessed at different soil depths in wetlands and farmland of the Yellow River Delta. SOC content decreased by 54% in the topsoil after converting wetland to farmland and there was little soil inorganic carbon (SIC enrichment). However, the contents and stocks of SOC and SIC in the subsoil were significantly enhanced in the red clay layer (RCL) in both land use types. The RCL also showed high accumulation rates of SIC (197 ± 95 g C m−2 yr−1), highlighting its importance in carbon sequestration in this large estuary. A negative correlation between SIC and δ13CSIC throughout the dataset and more negative values in the RCL indicate a larger contribution of secondary carbonate under C3 vegetation in the RCL. A positive correlation between SIC and SOC suggests that an enhancement of SOC may lead to an increase in SIC, especially in the subsoil YSL–RCL sequence with its relatively low SOC content. The RCL formed in the fluvial-deltaic sedimentary system with both higher carbonate content and stronger weathering intensity indicates that adsorption and precipitation of atmospheric derived carbonate on fine–grained suspended particulates may be important factors in carbonate accumulation.
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