Response of flow systems in soils to extreme atmosperical boundary conditions
Final Report Abstract
To analyzis the impact of changing climate conditions on flow patterns of water and solutes in soil experimental and model based approaches were applied. The impact of drying/rewetting and freezing/thawing cycles on flow patterns and time series was studied in the framework of the central manipulation experiments using tracer experiments, image analysis, extreme value statistics, and multivariate statistical analysis for flow patterns and nonlinear time series analysis for time series. Small scale heterogeneity and preferential flow were analyzed in column experiments under controlled laboratory conditions. A deterministic transport model was used for flux quantification and interpretation of field results. Unfortunately, simulations could not be continued for the second funding peridod due to severe damages of the experiment site (Kyrill) and changes in the soil hydroloical conditions. To analyse the impact of organic horizons, wettability and stones on the generation of preferential flow patterns in the framework of field tracer experiments VIS/NIR spectroscopy is used for high resolution in situ measurements of soil physical and soil chemical parameters. Detailled analyses were performed for wettability and contact angles. We analyzed temperatur and moisture effects on contact angles and wettability in laboratory experiments and studied spatial patterns of wettability and temporal changes of soil moisture and wettability in the context of the field manipulation experiments. Results may be summarized as follows: 1. Using Brillant Blue and iodide as tracers we were able to identiy distinct flow regions in soil. Along root macropores Brillant Blue and Iodide showed a good agreement in transport behaviour. Due to differences in sorption properties Brillant Blue transport was more focused to preferential flow paths than iodide (conservative tracer). 2. Quantification of flow pattens with dye coverage functions and extreme value indices was only partly successful. Improvements were possible by restriction of the analysis to the lower parts of the profiles and by including the scale parameter of the Pareto distribution. 3. Initial soil moisture and irrigation rates had a distinct impact on flow pattens. Flow pattern characterstics are further influenced by the spatial structure of organic top horizons and stones in the soil. Drying/rewetting and freezing/thawing did not reveal visible effects. 4. Statistical analysis of flow patterns was demanding and required the use of mixed effects model approaches with fixed and random effects. These analyses were carried out for soil texture, fine root density, dry bulk density, exchangeable cations, pH, Ctot, Ntot, and C:N ratio. Results showed significant differences and a good agreement of model estimates with measurements. 5. Dynamic column experiments under controlled conditions showed pronounced structure effects and clearly supportet the relevance of preferential flow for the laboratory scale. 6. Calibration results of water flux modelling for experimental treatments showed consistent results. Nonlinear time series analyses discovered considerable uncertainties and deviations from observed ecosystem behaviour. Modelling was not continued due to severe damages by strong storm events that also changed the hydrological characteristics of the site. 7. VIS/NIR spectra could successfully calibrated with measured values (contact angle, water drop penetration time, total organic carvon. PH, Fe, sand, silt, clay, Brillant Blue concentration, bulk density, soil moisture, soil texture). R2 values typically were in the range of 0.8 – 0.95. The spectrometer is used in the summer 2011 campaign for high resolution in situ measurements in the context of tracer experiments. 8. Comparisons of different methods for contact angle measurements and wettability showed good correlations. Temperature and moisture pretreatments of samples in laboratory experemints had a pronounced impact on water drop penetration time. Implications for field conditions are studied in an extensive measurement campaign in the context of the drought/irrigation experiments in 2011. 9. Spatial measurements of wettability and soil texture in a nested stratified random sampling design showed a clear spatial autocorrelation. The range exceeded diameter and distance of the manipulation plots. To which extent mixed effects models can be used to account also for these spatial effects is currently studied. 10. Contact angles in organic and mineral horizons are clearly different from zero. In Ah and O horizons mean values were greater than 90°. Maximum values approached 180°. Contact angles and hydrophobicity thus are assumed to have an considerable impact on infiltration behavior and moisture distribution in the forest soils under study (ongoing research in 2011).
Publications
- Analysing flow patterns from dye tracer experiments in a forest soil using extreme value statistics. European Journal of Soil Science 59(1), 103-113 (2008)
Bogner, C; Wolf, B; Schlather, M; Huwe, B
- Visualisation and analysis of flow patterns and water flow simulations in disturbed and undisturbed tropical soils. in Beck E., Bendix J, Kottke I, Makeschin F, Mosandl R,: Ecological Studies, Springer Verlag Vol. 198, 387-397 (2008)
Bogner, C; Engelhardt, S; Zeilinger, J; Huwe, B
- Effects of soil frost on nitrogen net mineralization, soil solution chemistry and seepage losses in a temperate forest soil. Global Change Biology 15, 825-836 (2009)
Hentschel, K; Borken, W; Zuber, T; Bogner, C; Huwe, B; Matzner, E
- Investigating flow mechanisms in a forest soil by mixed-effects modelling. European Journal of Soil Science 61, 1079-1090 (2010)
Bogner, C; Gaul, D; Kolb, A; Schmiedinger, I; Huwe, B
- Rapid estimation of Brilliant Blue concentrations in soil by vis diffuse reflectance spectroscopy. Geoderma 164, 95-98 (2011)
Bogner, C; Schmiedinger, I; Huwe, B
