Gas diffusivity in chinampas soils in Mexico City .

Abstract

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