Applicability of the soil gradient method for estimating soil–atmosphere CO2, CH4, and N2O fluxes for steppe soils in Inner Mongolia

摘要

For evaluating the applicability of the soil gradient method as a substitute for CO₂-, CH₄-, and N₂O-flux measurements in steppe, we carried out chamber measurements and determined soil gas concentration at an ungrazed (UG99) and a grazed (WG) site in Inner Mongolia, China. The agreement of the concentration-based flux estimates with measured chamber-based fluxes varied largely depending on the respective GHG in the sequence CO₂ CH₄ N₂O. A calibration of the gas-transport parameter used to calculate fluxes based on soil gas concentrations improved the results considerably for CO₂ and CH₄. After calibration, the average deviation from the chamber-based annual cumulative flux for both sites was 11.5%, 10.5%, and 59% for CO₂, CH₄, and N₂O. The gradient method did not constitute an adequate stand-alone substitute for greenhouse-gas flux estimation since a calibration using chamber-based measurements was necessary and vigorous production processes were confined to the uppermost, almost water-saturated soil layer.