Gas diffusivity in chinampas soils in Mexico City .


In this laboratory experiment we measured soil gas diffusion coefficients (D) on undisturbed cores of anthropogenic chinampas soils and tested the validity of some classical gas diffusivity models for predicting the ratio of D to the gas diffusion coefficient in free air (D0) as a function of the soil air-filled porosity (ε). The A1 horizon (0-7 cm) of chinampas soils had the highest gas diffusivity and a linear relationship between D/D0 and ε, and thus, the Penman model gave an adequate prediction for this sub-horizon. The Millington-Quirk model was similar to the D/D0 at all values of ε for the A2 sub-horizon (7-18 cm) and at ε < 0.5 cm3 cm-3 for the A3 (18-30 cm) and A4 (30-50 cm) sub-horizons. Gas diffusivities in chinampas soils were lower than in mineral soils, as predicted by D/D0(ε) models, likely due to the high content of soil organic carbon. The predictive models could be used for the evaluation of greenhouse gases emission from chinampas soil.
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