Vertical sections of CO2 (a) and O2 (b) concentrations showing the prevailing gas channels. Two different transects for the two different gases were chosen. (a) CO2 concentrations are shown in linear transect 4. Up to five CO2 channels can be seen from which four are reaching the soil surface. (b) Transect 6 is used to illustrate oxygen channels through the soil. CO2 concentrations are given in %.