Variation characteristics of CO2 in a newly-excavated soil profile,Chinese Loess Plateau: Excavation-induced ancient soil organic carbon decomposition

Soils of the Chinese Loess Plateau (CLP) contain substantial amounts of soil inorganic carbon (SIC), as well as recent and ancient soil organic carbon (SOC). With the advent of the Anthropocene, human perturbation, including excavation, has increased soil CO₂ emission from the huge loess carbon pool. This study aims to determine the potential of loess CO₂ emission induced by excavation. Soil CO₂ were continuously monitored for seven years on a newly-excavated profile in the central CLP and the stable C isotope compositions of soil CO₂ and SOC were used to identify their sources. The results showed that the soil CO₂ concentrations ranged from 830 μL·L^?1 to 11 190 μL·L^?1 with an annually reducing trend after excavation, indicating that the human excavation can induce CO₂ production in loess profile. The δ¹³C of CO₂ ranged from –21.27 ‰ to –19.22 ‰ (mean: –20.11‰), with positive deviation from top to bottom. The range of δ¹³C_SOC was –24.0‰ to –21.1‰ with an average of –23.1‰. The δ¹³C-CO₂ in this study has a positive relationship with the reversed CO₂ concentration, and it is calculated that 80.22% of the soil CO₂ in this profile is from the microbial decomposition of SOC and 19.78% from the degasification during carbonate precipitation. We conclude that the human excavation can significantly enhance the decomposition of the ancient OC in loess during the first two years after perturbation, producing and releasing soil CO₂ to atmosphere.