- BB
Authors: Berns, A.E.; Advisor: -; Participants: Mehmood, K.; Flath, A.; Hofmann, D.; Jacques, D.; Sauter, M.; Vereecken, H.; Engelhardt, I. (2018) - We identified undefined cation exchange as the dominant sorption process for Sr2+, followed by surface complexation on organic matter. These process‐based analyses were the basis for field‐scale simulations to predict the leaching risk of Cs and Sr radionuclides in agricultural soils under humid climate conditions. For both soils and radionuclides, the distribution coefficients (Kd) varied distinctly with time in shallow layers due to changes in temperature, saturation, and the prevailing dominant sorption processes. During a 3‐yr‐simulation period, 137Cs+ migrated to depths of 3.6 cm (silty loam) and 7.6 cm (sandy loam), while 90Sr2+ migrated to depths of 15.6 cm (silty loam) and 23.6 cm (sandy loam) due to competitive sorption of infiltrating Ca2+ and Mg2+ ions reducing 90Sr2+ sor...
|
- BB
Authors: Romano, N.; Advisor: -; Participants: Nasta, P.; Bogena, H.; De Vita, P.; Stellato, L.; Vereecken, H. (2018) - Rainy seasons are likely to be characterized by intense storms that trigger floods, resulting in increasing damage severity. The negative effects of anthropogenic disturbance on hydrological ecosystem services can be tempered by demand‐side adaptation options and appropriate investments to ensure water supply under drought conditions. To shed light on some of the scientific challenges related to these issues, a critical zone observatory (CZO) has been established in the Alento River catchment. Although sampling campaigns and monitoring investigations have been performed in this area for >25 yr, a more systematic research program was recently started to take comprehensive measurements in representative subcatchments of the study area. These sites are instrumented with advanced ground...
|
- BB
Authors: Rahmati, M.; Advisor: -; Participants: Pohlmeier, A.; Abasiyan, S.M.A.; Weihermüller, L.; Vereecken, H. (2019) - The results revealed that T2 spectra provided a good proxy to determine the PSD, showing good agreement between the PSD from T2 spectra and that calculated from the water retention curve (WRC) (R2 > 0.78; RMSE <1.38 μm). The application of CH also increased the zeta potential of the soil to −18.5 mV, compared with −20 mV obtained for the reference soil. The WRC measurements revealed that AG decreased the available water content for plant use compared with the reference soil, whereas CH increased the available water in comparison to the reference soil. Considering the parameters of the van Genuchten model, the application of AG and CH mainly affected the parameter α, confirming the dominant changes in macropores. This finding was confirmed by NMRR relaxation spectra. Furthermore, the...
|
- BB
Authors: Gao, Z.; Advisor: -; Participants: Haegel, F.H.; Esser, O.; Zimmermann, E.; Vereecken, H.; Huisman, J.A. (2019) - The measured SIP spectra as a function of saturation were interpreted by fitting a Cole–Cole model to the low‐frequency part of the SIP measurements. The porous nature of the biochar particles strongly affected the SIP response of the partially saturated sand–biochar mixtures. Due to the high residual water content of the biochar in a dry background, the relationship between bulk electrical conductivity and water saturation was nonlinear in a log–log representation. This nonlinear behavior could adequately be explained with a dielectric mixing model that considered the drainage of the biochar particles. Both the measured phase and chargeability of the sand–biochar mixtures showed a complex dependence on water saturation. This was attributed to the decrease in polarization strength o...
|
- BB
Authors: Wang, J.; Advisor: -; Participants: Bogena, H.R.; Vereecken, H.; Brüggemann, N. (2018) - The dynamics of redox potential were induced by changing the water‐table depth in a laboratory lysimeter. Before fertilization during saturated conditions, we found a clear negative correlation between redox potentials and N2O emission rates. After switching from saturated to unsaturated conditions, N2O emission quickly decreased, indicating denitrification as the main source of N2O. In contrast, the emissions of CO2 increased with increasing soil redox potentials. After fertilization, N2O emission peaked at high redox potential, suggesting nitrification as the main production pathway, which was confirmed by isotope analysis of N2O. We propose that redox potential measurements are a viable method for better understanding of the controlling factors of GHG emissions, for the different...
|
- BB
Authors: Landl, M.; Advisor: -; Participants: Schnepf, A.; Uteau, D.; Peth, S.; Athmann, M.; Kautz, T.; Perkons, U.; Vereecken, H.; Vanderborght, J. (2019) - The model was calibrated against observed root length densities in both the bulk soil and biopores by optimizing root growth model input parameters. By implementing known interactions between root growth and soil penetration resistance into our model, we could simulate root systems whose response to biopores in the soil corresponded well to experimental observations described in the literature, such as increased total root length and increased rooting depth. For all considered soil physical (soil texture and bulk density) and environmental conditions (years of varying dryness), we found biopores to substantially mitigate transpiration deficits in times of drought by allowing roots to take up water from wetter and deeper soil layers. This was even the case when assuming reduced root ...
|
- BB
Authors: Vereecken, H.; Advisor: -; Participants: Weihermüller, L.; Assouline, S.; Šimůnek, J.; Verhoef, A.; Herbst, M.; Archer, N. (2019) - . We still lack a consistent theoretical framework to predict effective fluxes and parameters that control infiltration in LSMs. Our analysis shows that there is a large variety of approaches used to estimate soil hydraulic properties. Novel, highly resolved soil information at higher resolutions than the grid scale of LSMs may help in better quantifying subgrid variability of key infiltration parameters. Currently, only a few LSMs consider the impact of soil structure on soil hydraulic properties. Finally, we identified several processes not yet considered in LSMs that are known to strongly influence infiltration. Especially, the impact of soil structure on infiltration requires further research. To tackle these challenges and integrate current knowledge on soil processes affecting...
|
- BB
Authors: Cai, C.; Advisor: -; Participants: Vanderborght, J.; Couvreur, V.; Mboh, C.M.; Vereecken, H. (2018) - These models were implemented in HYDRUS‐1D, and soil hydraulic parameters were optimized by inverse modeling using soil water content and potential measurements and observations of root distributions of winter wheat (Triticum aestivum L.) in horizontally installed rhizotubes. Soil moisture was equally well predicted by the three models, and the soil hydraulic parameters optimized by the models with compensation were comparable. The obtained RWU parameters of the Feddes–Jarvis model were consistent with data reported in the literature, although the pressure heads h3l and h3h for lower and higher transpirations rates, respectively, could not be uniquely identified. Response surfaces of the objective function showed that the root‐related parameters of the Couvreur model could be identi...
|
- BB
Authors: Brunetti, G.; Advisor: -; Participants: Šimůnek, J.; Bogena, H.; Baatz, R.; Huisman, J.A.; Dahlke, H.; Vereecken, H. (2019) - In recent years, cosmic‐ray neutron sensing (CRNS) has proven to be a reliable method for the estimation of area‐average soil moisture at field scales. However, its use in the inverse estimation of the effective SHPs is largely unexplored. Thus, the main objective of this study was to assess the information content of aboveground fast‐neutron counts to estimate SHPs using both a synthetic modeling study and actual experimental data from the Rollesbroich catchment in Germany. For this, the forward neutron operator COSMIC was externally coupled with the hydrological model HYDRUS‐1D. The coupled model was combined with the Affine Invariant Ensemble Sampler to calculate the posterior distributions of effective soil hydraulic parameters as well as the model‐predictive uncertainty for dif...
|
- BB
Authors: Groh, J.; Advisor: -; Participants: Stumpp, C.; Lücke, A.; Pütz, T.; Vanderborght, J.; Vereecken, H. (2018) - We used different optimization strategies to investigate which observation types are necessary for simultaneously estimating soil hydraulic and solute transport parameters. Combining water content, matric potential, and tracer (e.g., δ18O) data in one objective function (OF) was found to be the best strategy for estimating parameters that can simulate all observed water flow and solute transport variables. A sequential optimization, in which first an OF with only water flow variables and subsequently an OF with transport variables was optimized, performed slightly worse indicating that transport variables contained additional information for estimating soil hydraulic parameters. Hydraulic parameters that were obtained from optimizing OFs that used either water contents or matric pot...
|
