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Multidimensional visualization of preferential flow pathways using neutron and x-ray radiation
(2016)
The occurrence of preferential flow of water in soils is rather the rule than the exception particularly in heterogeneous structured soils. The quantitative prediction is difficult because of the spatial as well as temporal variability. One aim of the dissertation was to visualize the soil structure and flow patterns in mine soils using a combination of neutron radiography, neutron tomography and x-ray computed tomography experiments. Both radiation techniques were used to describe preferential pathways as a soil structure with CT and the process of preferential flow of water with NT. For the first time neutron radiation was applied on undisturbed soil cores to visualize water distributions in natural soils on three examples for heterogeneities of different origin.
In a first investigation we used neutron radiography to analyze the moisture distribution in undisturbed slab-type and cylindrical samples of mine soils containing lignitic fragments and inclined soil layers. 2D radiography sequences indicated that flow pathways are highly dependent on the shape, distribution, and internal structure of the lignitic fragments. For 3D experiments, the quantitative analysis of water contents failed due to a pronounced beam hardening effect. The tensiometer data indicated the existence of local non-equilibrium in pressure heads between fragments and matric pore regions.
The objective of the second study was to analyze and visualize the effects of initial soil structure formation at the surface of bare soils in an artificial hydrological catchment that has been left to undirected ecological succession for three years. The three-dimensional (3D) micro-morphology was described using the X-ray computed tomography (CT); two-dimensional (2D) infiltration patterns were obtained from drip infiltration experiments using time-resolved neutron radiography (NT). The analyses of CT data indicate the existence of (i) structural crusts on soil consisting of sandy to loamy sediments and (ii) depositional crusts on sandy sediments. The results of combined observations using CT and NT suggest that the initial soil surface structure alterations of young sandy sediment modify moisture patterns of infiltrating water only slightly.
The aim of the 3rd experiment was to study effect of two ‘ecological engineers’, moss vegetation and beetle larvae on pore structure and infiltration. The soil pore structure was characterized by micro-computed tomography analyses of bare soil, sparse and dense moss-vegetated samples containing a single burrow. Flow patterns of infiltration experiments were visualized using the neutron radiography technique. The results of this study suggest that moss vegetation and burrowing activity of ground beetles strongly control the initial soil development by modification of pore structure and surface water infiltration.
In regionalen Klimamodellen wird die untere Randbedingung durch Bodenmodelle bereitgestellt. Diese beinhalten Modellformulierungen, die eine große Anzahl an Eingabeparametern benötigen. Die exakte Bestimmung dieser Parameter stellt ein Problem dar, da sie für ein großes Gebiet in hoher räumlicher und teilweise zeitlicher Auflösung erfolgen muss. Die unterschiedlichen Bestimmungsmethoden tragen dazu bei, dass für viele Oberflächen- und Bodenparameter nur ein möglicher Wertebereich angegeben werden kann. Die Auswirkungen dieser ungenauen Kenntnis der Parameter auf die Ergebnisse regionaler Klimasimulationen mit dem CLM wurden untersucht. Für den LAI, den Vegetationsbedeckungsgrad, die Wurzeltiefe, die Vegetationsalbedo, den Stomatawiderstand, die Bodenart und die Wärmeleitfähigkeit konnten Veränderungen der Modellergebnisse im Jahresmittel von 2-6 W/m^2 der Energiebilanzgrößen und 0,25 K der 2m-Temperatur nachgewiesen werden. Im Monatsmittel ergeben sich Veränderungen bis 20 W/m^2 für die turbulenten Wärmeflüsse und bis 1,5 K für die 2m-Temperatur. Es konnte gezeigt werden, dass die resultierenden Unsicherheiten in den Modellergebnissen dabei räumlich und zeitlich variieren und stark vom Bodenwassergehalt beeinflusst werden. Die Benutzung zweier neuer Parameterdatensätze führte in den Simulationen zu einer Erwärmung bis 0,5 K im Jahresmittel und konnte damit die gegenüber Beobachtungsdaten vorhandene Temperaturabweichung von 1,5 K des Modells reduzieren.
Desertification is seen as a severe threat to Mediterranean ecosystems and the desert fringes. Both land use and climate variations may lead to an advance of the desert, and human and natural factors can be connected in feedback relationships. This makes it difficult to describe cause-and-effect relationships, and to predict the impact of global warming. A key is understanding historic desertification, since the investigation of the past allows to better separate the roles of man and weather. These questions were investigated in the Decapolis region in northern Jordan, an area in the transition zone between the Arabian desert and the Mediterranean climate belt. It had been assumed that historic desertification in the Decapolis was connected with severe degradation of soils, and caused by agricultural mismanagement and deforestation. This idea served as explanation for economic decay and abandonment of cities, too. However, the greatest part of the erosion took place during the last Ice Age and the Younger Dryas. There is no indication that the inanimate landscape changed significantly since the Bronze Age. Historic field systems were partially preserved and seem reflected by distinct soil development, indicating that the impact of land use was more complex and less devastating than previously assumed. Historic human impacts on the natural environment seem limited, and certainly not connected with desertification. Romantic northern European misconceptions of how a "natural" landscape should look like may in this context have contributed to a negative assessment of traditional agriculture in the Mediterranean. Comparative analyses of soils and colluvia, air photos, historic travel reports, tree rings and climate reconstructions indicate that population growth was behind the flourishing of the Decapolis, which took place mostly under favourably stable climatic conditions. Periods of decline seem triggered by climatic anomalies. As it seems, climate change was previously understood too linearly: extreme rainfall events can be more devastating than drought, and temperature, wind and rainfall distribution over the year are important as well. Cool and dry periods at the end of the last Ice Age were connected with incision and sometimes dramatic erosion. Climatic fluctuations during history may have been connected with pests, famines, plagues, and wars which caused dramatic drops of population levels. The ecological sensitivity of the desert belt may have aggravated the impact of climate variations. Economic recovery took place only when population levels rose again. It is so far unknown how climate will develop under global warming, but an increasing number of anomalous events could have dramatic impacts. The key for dealing with global warming seems therefore adaptation to climatic irregularities.
Die Verbesserung bindiger Böden mit Kalk im Planumsbereich von Verkehrsflächen hat sich seit vielen Jahren in der Praxis nicht nur kurzfristig, sondern auch langfristig bewährt. Es stellte sich daher die Frage, unter welchen Bedingungen und in welchem Umfang bei der Ausführung von Kalkverbesserungen die Dicke des frostsicheren Oberbaus reduziert werden kann. Voraussetzung hierfür ist, dass das Boden-Kalk-Gemisch keine schädlichen Frosthebungen verursacht und dauerhaft eine ausreichende Tragfähigkeit gewährleistet. Im Rahmen des Versuchsprogramms wurden Verkehrsflächen mit kalkbehandeltem Planum, die mehrjährigen Belastungen aus Verkehr und Klima unterworfen waren, erfasst und analysiert. An den Strecken wurden Zustandsbewertungen, Aufgrabungen und Tragfähigkeitsmessungen durchgeführt sowie ungestörte Proben aus dem Planum und gestörte Proben des unbehandelten Ausgangsbodens für Laborversuche entnommen. Im Labor wurden mineralogische Veränderungen sowie das Verhalten der kalkbehandelten Böden gegenüber Wasser und Frost untersucht und mit den unbehandelten Ausgangsböden verglichen. Die kalkbehandelten Böden wurden Frostempfindlichkeitsklassen nach ZTVE-StB zugeordnet, und Beziehungen zu den beim Einbau vorliegenden stofflichen, technischen und technologischen Bedingungen wurden ermittelt. Daraus und aus Ergebnissen weiterer Versuchsreihen wurden Kriterien abgeleitet, unter denen eine Verbesserung des Erdplanums mit Kalk die Dicke des frostsicheren Oberbaus reduzieren kann.