## 3 Results and Discussion
#### 3.1.1 Time Series and Seasons  
We present typical examples and interpretations of selected data from the Spruce monitoring plot at the ES site (Figure 4). All data were quality checked and filtered so that the different gases presented in this example cover different time slots. N\({}_{2}\) and Ar are not shown since they were only used for quality assurance purposes. O\({}_{2}\) concentrations always decreased with depth indicating consumption of O\({}_{2}\) by the soil (Figure 4). A clear seasonality in O\({}_{2}\) concentrations was registered (Figure 5) with O\({}_{2}\) concentrations reaching down to 200,000 ppm (20%), which is approx. 8000 ppm below the atmospheric concentration of O\({}_{2}\) (Figure 4). This means, this soil was always well-aerated. Soil CO\({}_{2}\) showed an opposite course and clearly increased in concentration with depth throughout the entire time series (Figure 5). CO\({}_{2}\) concentrations ranged from 400 ppm near the soil surface to 10,000 ppm in 10 cm depth. Soil CO\({}_{2}\) also shows a typical seasonality with much higher concentrations in the summer when temperatures and soil respiration is highest (Figure 5). Figure 4: Time series of the soil gas profile at the ES spruce plot showing the course of average concentrations of O\({}_{2}\), CO\({}_{2}\), CH\({}_{4}\), N\({}_{2}\)O and C\({}_{2}\)H\({}_{4}\) at different positions in the mineral soil (\(-10\), \(-5\), MS), in the humus layer (0, 3, HL), and in the atmosphere (ATM). CO\({}_{2}\), O\({}_{2}\) and N\({}_{2}\)O concentration measurements cover almost the entire observation period, while technical difficulties limit the data availability of CH\({}_{4}\) and C\({}_{2}\)H\({}_{4}\) concentrations. concentrations could be due to a strong local CH\({}_{4}\) source e.g., an industrial area, a biogas plant or peatland. It could also partly result from the relative uncertainty of the calibration gas and other artefacts. The apparently elevated atmospheric CH\({}_{4}\) concentration had only an indirect effect since our monitoring and flux calculation approach rather relies on detecting vertical gradients than measuring the absolute concentration. To find out about or source of CH\({}_{4}\) or possible artefact we are currently planning CH\({}_{4}\) measurements with an independent gas analysis system. The time series of N\({}_{2}\)O neither showed a clear seasonality nor clear depth gradients. They often showed a very weak increase in concentration with depth, yet the variability at a given depth was often in a similar range (Figure 4). Calculating a seasonal average course from the entire time series (Figure 5) showed that this weak increase with depth was persistent during most of the seasons, which is an indication of an ongoing weak mean denitrification and production of N\({}_{2}\)O. Reliable measurement of soil C\({}_{2}\)H\({}_{4}\) concentrations (above the detection limit) could be collected only after 2017 at this site (Figure 4). Most values of C\({}_{2}\)H\({}_{4}\) measurements were below the detection limit which is normal for a well aerated soil. Despite the good supply of O\({}_{2}\) we detected concentrations of up to 6 ppm of C\({}_{2}\)H\({}_{4}\). C\({}_{2}\)H\({}_{4}\) concentrations seemed to have higher values in winter (Figure 5) when soil water content was higher and soil gas diffusivity lower. In summer, when soil temperature peaked and soil microbial activity was highest, C\({}_{2}\)H\({}_{4}\) concentrations also seemed to become temporarily higher. The detected C\({}_{2}\)H\({}_{4}\) concentrations of up to 6 ppm in the humus layer can be considered as a high value [27]. We think that the production of C\({}_{2}\)H\({}_{4}\) occurs at hot spots similar to the production of N\({}_{2}\)O. This is in contrast to the more or less evenly distributed production CO\({}_{2}\) or consumption of O\({}_{2}\) which results in more homogenous soil gas profiles. Calculating C\({}_{2}\)H\({}_{4}\) fluxes or production rates was not feasible due to the limited data and its small-scale processes.