## 3 Results and Discussion  
### Hydraulic Behavior  
Water content observations (Figures 2 and 3, Supplementary Materials S2) indicate that the periods with higher values, caused by the daily infiltrations of only TWWE in the morning and evening hours, are followed by much longer periods of lower water content. These periods with higher and lower values are resulting from daily wet and dry phases, respectively. Moreover, the intermittent infiltrations (see Supplementary Materials S1) cause oscillations of water content in the upper observation points (Obs1). The retention of water in the dry phases is observed much lower in the soil with more permeability and smaller proportion of fine pores (Figure 3) than in the soils with lower permeability and higher fine pore content (Figure 2). Furthermore, the results indicate that periods with water contents close to full saturation are not existent, and thus, sufficient oxygen supply is expected during the infiltration of TWWE only. Depending upon the hydraulic conductivity of the soils, it is already evident that the daily fluctuations of water content are influenced due to precipitation events. In case of the more intensive (event 2) and longer (event 3) events, steep increases in water content for both observation points are observed (Figure 2B,C and Figure 3B,C). However, these high soil moisture contents, less appropriate for high biological activity, decline rapidly after the end of the precipitation events. Therefore, it can be concluded that water contents are only temporally affected by the additional infiltration of water originating from precipitation events. In the course of evaluating the obtained data, it should also be taken into account that 1D-column experiments may lead to an overestimation of water content compared to real-world conditions due to their dimensionality. The restricted lateral flow of the infiltrated water can lead to a higher degree of saturation [34; 35]. Furthermore, preferential flow paths, such as the sidewall flow, can affect sensors positioned close to the sidewall [36; 37]. A good agreement between observed and predicted water content for the upper observation point was achieved. However, for the lower observation point, the simulated water content showed a constant offset from observations but indicated a similar pattern of moisture fluctuations. One of the reasons could be the compaction of soils causing the apparent change of observed moisture distribution in the lower half of the column systems. Overall, the model outputs indicate that the time patterns of the fluctuating water contents during the joint infiltration of both TWWE and the additional water originating from precipitation events are in a moderate to good agreement. (Figures 2 and 3, Supplementary Materials S2). Besides visual comparison, two error indicators were calculated to assess the quality of the conformity between observed and simulated water contents. Root Mean Square Error (RMSE), one of the commonly used error indicators, shows how well the simulated data represent the pattern of the observed data [38]. In principal applications, the lower the RMSE, the better the model performance [39]. In addition, percent bias (PBIAS), expressed as a percentage, assesses the averaged trend of the simulated data to be larger or smaller than the observed values [40]. The optimal value of PBIAS is zero, indicating accurate model simulation. In the case of positive values, the model is underestimating the water content while the model is overestimating the water content in case of negative values. PBIAS values up to \(\pm\) 25% can be considered as good to moderate fit [39]. The error indicators were calculated for the total simulation time of 168 h in the course of a precipitation event to see the overall trend of the fluctuating water contents including phases with normal TWWE infiltration as well as the joint infiltration of both TWWE and the additional water.