Variability of concentrations of gases in the air of the vadose zone in the natural and agriculturally converted environments

The paper presents results of studies of gas concentrations in soil air of the vadose zone (O2, CO2, CH4, H2S, NH3) in natural (alder swamp and dune) and agriculturally modified (plough fields, permanent grassland) environments. Basing on the results of the field measurements dependence of gas exchange between aeration zone and atmosphere can be observed. Limited gas exchange between atmosphere and aeration zone results in increase of CO2 concentration and decrease of O2 content. The processes that regulate the concentrations of CO2 and O2 are: [1] variations of the temperature of the atmosphere and soil, [2] variations of soil moisture, [3] variations of atmospheric pressure. The oxygen concentration in the vadose zone decreases with increasing depth, while the CO2 concentration increases. Analysis of the distribution of gases in the vadose zone against the mean daily temperature shows that the O2 concentration was lower during cooler periods than during warm periods. An increase of soil moisture (e.g., resulting from the precipitation infiltration) is related to the O2 concentration decrease and CO2 concentration increase resulting from unfavourable conditions of gas exchange between soil and the atmosphere