Impact of wind speed and soil permeability on aeration time in the upper vadose zone

In high permeability soils, gas flux through the Earth-atmosphere interface can be significantly greater than expected from only diffusion. One mechanism that can contribute to the overall flux increase is wind-induced transport (WIT). Here, we explored the magnitude of WIT as a function of the averaged wind speed and soil permeability. Five columns, each filled with homogeneous dry soil or soil-aggregates with different permeability were installed in a bare field. The permeabilities in the columns ranged from 3.87 x 10(-10) m(2) (sand) up to 2.67 x 10(-6) m(2) (large aggregates collected from a nearby agricultural field). CO2-enriched air was used to quantify air transport in each soil column. Measurements were carried out under natural wind conditions. Data collected included atmospheric (wind speed, air temperature, barometric pressure, etc.) and soil parameters inside the columns (temperatures and CO2 concentration at -0.2 m). Data of changing CO2 concentration over time were compared to (1) an analytical diffusion transport solution, and (2) a numerical advection-dispersion solution. Results show that for sand, air transport was governed by diffusion with a very small additional WIT effect, increasing total air transport by up to similar to 25% for cases of high wind speed (> 5 m/s). From the permeability of small gravel and above (>= 1.02 x 10(-8) m(2)), WIT dominated air transport and the effect of WIT was clear even under low wind speeds. The increase in total air transport in the large aggregates for high wind speed was up to one order of magnitude greater than pure diffusive transport.