Direct Observation of Wind-Induced Pressure-Pumping on Gas Transport in Soil

Core Ideas We directly observed the effect of wind-induced pressure-pumping on gas transport in soil. Mean above-canopy wind speeds >3 m s−1 increase the soil gas transport rate by about 10%. We generally recommend considering the pressure-pumping effect in gas flux measurements. Soil gas transport is commonly assumed to be governed by molecular diffusion. However, nondiffusive transport processes such as wind-induced pressure-pumping can significantly enhance soil gas transport during periods of high wind speed. During a field campaign at a forest site, we combined methods to measure soil gas transport, air pressure, and airflow characteristics. We directly observed the enhancement of gas transport due to wind-induced air pressure fluctuations during two periods when mean above-canopy wind speeds exceeded 3 m s–^91. Specifically, we measured an increase of the topsoil gas diffusivity of about 10%. The wind-induced air pressure fluctuations, which were responsible for pressure-pumping, had frequencies of 0.02 Hz and amplitudes up to 5 Pa. Overall, our results show that wind-induced pressure-pumping can substantially increase the commonly diffusion-limited transport rate of soil gases. We therefore recommend considering this process in gas flux measurements in the field and in the laboratory.