Soil Science Society of America Journal Soil Sci. Soc. Am. J.81:770–774 doi:10.2136/sssaj2017.01.0034n Received 25 Jan. 2017. Accepted 29 Mar. 2017. *Corresponding author (thomas.laemmel@bodenkunde.uni-freiburg.de). © Soil Science Society of America, 5585 Guilford Rd., Madison WI 53711 USA. All Rights reserved. Direct Observation of Wind-Induced Pressure-Pumping on Gas Transport in Soil Soil Physics & Hydrology Note Soil gas transport is commonly assumed to be governed by molecular diffusion. However, nondiffusive transport processes such as wind-induced pressure- pumping can signifcantly enhance soil gas transport during periods of high wind speed. During a feld campaign at a forest site, we combined methods to measure soil gas transport, air pressure, and airfow characteristics. We directly observed the enhancement of gas transport due to wind-induced air pressure fuctuations during two periods when mean above-canopy wind speeds exceed- ed 3 m s –^91 . Specifcally, we measured an increase of the topsoil gas diffusivity of about 10%. The wind-induced air pressure fuctuations, which were respon- sible 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 substan- tially increase the commonly diffusion-limited transport rate of soil gases. We therefore recommend considering this process in gas fux measurements in the feld and in the laboratory. Abbreviations: PPC, pressure-pumping coeffcient; PPE, pressure-pumping effect; SWC soil water content. G as exchange between the soil and the atmosphere is of major interest in the current perspective of climate change (Smith et al., 2003). Molecular diffusion is commonly assumed as main transport process of soil gases (Buckingham, 1904). However, studies showed that nondiffusive gas transport processes can substantially enhance soil gas transport. Studies have shown that (i) advection can be generated by rapid changes in barometric air pressure associated with the passage of frontal systems (Clements and Wilkening, 1974), (ii) advec- tive movement of air in surface layers can also be generated by high wind speeds in highly porous material such as moss (Hirsch et al., 2004) or mulch (Novak et al., 2000), and (iii) wind-induced pressure-pumping (Massman et al., 1997) can enhance soil gas transport by dispersive mixing of soil air when air pressure fluctua- tions propagate through the air-filled soil pores (Maier et al., 2012). Only a few studies have quantified the pressure-pumping effect (PPE) on gas transport in the soil. Under controlled conditions, Kimball and Lemon (1971a) used a tracer gas to study the PPE in different artificial substrates, whereas Maier et al. (2012) used artificial airflow in a laboratory experiment with soil samples. In the field, the PPE was observed only indirectly by soil CO 2 concentration mea- surements (Baldocchi and Meyers, 1991; Bowling and Massman, 2011; Bowling et al., 2009; Maier et al., 2010). However, changes in CO 2 concentration as an indica- tor for transport processes imply high uncertainties because CO 2 concentrations are affected by both CO 2 production and transport. The aim of this study was to directly quantify the PPE on soil gas transport in the field using an inert tracer gas and to relate it to air pressure and airflow characteristics. T. Laemmel* Soil Ecology Univ. of Freiburg Bertoldstrasse 17 79098 Freiburg Germany M. Mohr Environmental Meteorology Univ. of Freiburg Werthmannstrasse 10 79085 Freiburg Germany H. Schack-Kirchner Soil Ecology Univ. of Freiburg Bertoldstrasse 17 79098 Freiburg Germany D. Schindler Environmental Meteorology Univ. of Freiburg Werthmannstrasse 10 79085 Freiburg Germany M. Maier Soil Ecology Univ. of Freiburg Bertoldstrasse 17 79098 Freiburg Germany 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 fux measurements. Published online August 31, 2017