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

Abstract

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 11190 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 δ13CSOC 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.

Keywords

• soil organic matter
• human excavation
• soil co2
• stable carbon isotopic composition
• china loess plateau