Effect of Wind on Soil-Atmosphere Gas Exchange

Global climate change in recent decades is accompanied by rising temperatures and increasing cyclonic activity with strong air flows. How do they affect soil respiration? Is it possible to expect an increase in CO2 emissions and, consequently, a positive feedback of climate change through the greenhouse effect? These questions cannot be answered without the insight into the effect of wind speed on the gas exchange between soil and atmosphere in different landscapes. The paper summarizes the long-term measurements of CO2 efflux from forest-steppe chernozems (Kursk oblast, Russia) in natural and anthropogenic landscapes with forest or herbaceous vegetation depending on wind speed; it presents a physically grounded approach to its quantitative first-approximation (linear) description. The approach assumes an impact of wind through increased forced convection and turbulent diffusivity along with a potential reduction in diffusion mass transfer due to a decrease in the gradient of CO2 concentration between the atmosphere and soil. The constructed inverse parabolic dependence adequately describes the empirical data and assumes a twofold increase in the emission with the wind speed increase to the critical value of 3 m/s and its decreases to the initial level with the further wind speed increase to 6-7 m/s. The intensity of forced convection of soil air turns out to be by five-six orders of magnitude lower than the wind speed in the atmosphere but not inferior to the intensity of conventional isothermal CO2 diffusion, which suggests that this mechanism is to be taken into account in the models of soil-atmosphere gas exchange.