Canopy Gas Exchange: Gas Exchange with Soil

Modeling Gas Flow Velocities in Soils Induced by Variations in Surface Pressure, Heat, and Moisture Dynamics

“…Figure 3 shows the COM estimates of v p (0) from Equation , v T (0) from Equation , and v θ (0) from Equation for the June 2012 study period. The takeaways here are that (a) | v p | ≫ | v T | and | v θ |, as might be expected for a soil with a permeability >10 −12 m 2 , and (b) the COM estimate of | v T | agrees more closely with Kimball (1983) than with the estimate based on the thermally induced flow (Section 2.2.2). A less obvious takeaway is that during periods of rain (also see Figure 1 and in particular Figure 2) that | v θ | ≈ | v T |.…”

“…(2013) use a similar approach to estimate the advective velocity of thermally induced flow in stream beds. Also relevant here is the estimate of | v T | that can be derived from Kimball (1983), which is $$$\vert {v}_{T}\vert \approx (0.1)\times 1{0}^{-6}\,{\mathrm{m}\mathrm{s}}^{-1}\quad (\mathrm{K}\mathrm{i}\mathrm{m}\mathrm{b}\mathrm{a}\mathrm{l}\mathrm{l},\ 1983)$$$ This is roughly two orders of magnitude smaller than the preceding estimate of v T . This difference will be discussed further in Section 4.…”

“…But within soils the gas‐filled pore volume can change whenever soil water changes phase, that is, during evaporation or condensation, and during rainfall or irrigation and the concomitant movement of water through the soil matrix. These temperature and moisture influences on induced advective flows have been considered by a few authors, for example, Kimball (1983), Parlange et al. (1998), Jury and Horton (2004), and Novak (2016) all explore possible temperature effects and Lebeau and Konrad (2009) include the possibility of dynamic changes in soil moisture as part of their modeling study.…”

“…Second, beyond the mechanical forcing of soil by fluctuations in atmospheric pressure at the soil surface, surface heating can force temperature variations within permeable media and thereby also induce advective flows in both soil (e.g., Hinkle, 1994; Kimball, 1983; Novak, 2016; Parlange et al., 1998) and snowpacks (e.g., Bartelt et al., 2004; Gray & Morland, 1994; Massman et al., 1997). This is easily understood from the ideal gas law.…”

Model–data fusion approach to quantify evapotranspiration and net ecosystem exchange across the sagebrush ecosystem at different temporal resolutions

“…Across semi‐arid ecosystems, precipitation integrated over a 7‐day period provides an assessment of soil moisture conditions (either wet or dry spell) and can strongly influence ET or NEE (Baldocchi et al, ; Brubaker & Entekhabi, ; Fennessy & Shukla, ). Similarly, at weekly time step, change in air pressure from fronts influences the diffusion of carbon dioxide from soil (Baldocchi et al, ; Kimball, ). We did not have sufficient empirical data to justify the incorporation of the above‐mentioned processes within the model structure.…”