## 3 Results and Discussion
#### 3.1.2 Typical Soil Gas Profiles  
Soil water content, soil temperature and soil gas diffusivity are important drivers and underlay seasonal cycles (Figures 5 and 6). \(D_{\text{S}}\)/\(D_{0}\) is highest in the humus layer and lower in the deeper mineral soil layers (Figure 6 top). This is an effect of the decrease in total pore space with depth which results from the load of the soil above [45,65]. \(D_{\text{S}}\)/\(D_{0}\) is decreasing with depth within each layer because soil water content is usually increasing with depth. The typical \(D_{\text{S}}\)/\(D_{0}\) profile changes through the seasons. The wet seasons of spring and winter have higher soil water contents and thus lower \(D_{\text{S}}\)/\(D_{0}\) values than the warmer and drier seasons of summer and fall (Figures 5 and 6). Soil gas profiles data (O\({}_{2}\), CO\({}_{2}\), CH\({}_{4}\) and N\({}_{2}\)O) were grouped according to their season (Figure 6). Seasonal average values per sampler were calculated instead of monthly averages of all five samplers per depth (as shown in Figure 5) to represent the variability covered by the replications. That means variability of the green dots at a given depth shown in Figure 6 represents the average spring concentration of one specific sampler at a given depth. This allows assessing the homogeneity of the soil gas profiles and gives some information on possibly simultaneously occurring processesFigure 6: Typical seasonal soil profiles of (top) soil gas diffusivity (\(D_{\text{S}}\)/\(D_{\text{O}}\)) and (below) soil gas concentrations of O\({}_{2}\), CO\({}_{2}\), CH\({}_{4}\) and N\({}_{2}\)O. Seasons are indicated by colours for spring (green), summer (yellow), fall (brown) and winter (blue). Each dot represents the average seasonal value of one sampler. Vertical lines connect average values per depth. O\({}_{2}\) decreased with depth in all seasons, similar to the increase in CO\({}_{2}\) with depth. The CO\({}_{2}\) and O\({}_{2}\) gradients are much stronger in summer than in winter and spring. Average summer concentrations of CO\({}_{2}\) and O\({}_{2}\) of all samplers are clearly different from winter concentrations (blue and yellow dots do not mix), because the strong seasonal cycle dominates the variability of each sampler at all depths. The O\({}_{2}\) gradient is strongest during summer and lowest O\({}_{2}\) values were registered in 10 cm depth in the summer seasons, as observed in the seasonal time course of soil gas concentrations (Figure 4). Seasonal soil CO\({}_{2}\) concentrations were very similar to the O\({}_{2}\) profiles but had slightly bigger differences between the winter and spring profiles than the O\({}_{2}\) data (Figure 6). The CO\({}_{2}\) concentrations of all samplers showed a persistent ranking over time according to their depth, but also at each depth (data not shown). The lower absolute precision of the concentration measurement of O\({}_{2}\) compared to CO\({}_{2}\) resulted in a slightly larger scattering of daily profiles, which was smoothed out by averaging seasonal O\({}_{2}\) profiles in Figures 5 and 6. Yet, daily O\({}_{2}\) profiles included a higher uncertainty in the concentration measurement than CO\({}_{2}\) profiles. The seasonal soil CH\({}_{4}\) concentrations showed an almost constant profile all year round with a linear decrease in CH\({}_{4}\) concentration from the soil surface to 5 cm depth (Figures 5 and 6) which means that the gradients did not vary too much over time and within the top soil. One of the five samplers at 10 cm depth had average CH\({}_{4}\) concentrations from 1.7 to 1.8 ppm throughout the seasons while all other samplers always had CH\({}_{4}\) concentrations below 1.5 ppm. This indicates either (a) a weak local net production of CH\({}_{4}\) near this sampler while net consumption of CH\({}_{4}\) dominated the rest of the soil gas profile, (b) less CH\({}_{4}\) consumption above this sampler, or (c) a locally higher soil gas diffusivity above the sampler.