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94 CHAPTER 3. TERRESTRIAL SYSTEMS
3.1 Soil Physics
Group members
Prof Dr. Kurt Roth, head of group
Angelika Gassama, Staff
Dipl. Phys. Holger Gerhards, PhD student
Moritz Mie, diploma student
Dipl. Phys. Fereidoun Rezanezhad, PhD student
Dipl. Geol. Philip Schiwek, PhD student
Dipl. Phys. Klaus Schneider, PhD student
Carolin Ulbrich, diploma student
Dr. Hans-Jrg Vogel, Post Doc, on leave
Dr. Ute Wollschlger, Post Doc
Abstract
We (i) experimentally study transport processes in soils and groundwater – water, solutes, heat – from
the lab- to the field-scale, (ii) develop and apply methods for near-surface geophysical exploration and
monitoring, and (iii) explore the thermal and hydraulic dynamics of permafrost on the Tibetan plateau
with a focus on climate warming.
Scientific Objectives
1. Qualitatively understand flow processes beyond the classical Richards-regime, specifically gravitydriven
flow instabilities and the dynamics of the capillary fringe.
2. Quantify effective hydraulic material properties for a very wide range of hydraulic states.
3. Develop ground-penetrating radar (GPR) for directly measuring soil water content and electrical
resistivity tomography (ERT) for quantitative monitoring of solute transport.
4. Monitor and qualitatively understand the dynamics of the permafrost in the wet and comparatively
warm region of the Eastern Tibetan plateau.
Overarching topic
To contribute to the fundamental understanding of transport processes in terrestrial systems, mostly
soils. These may be characterized as strongly and stochastically forced processes with a highly nonlinear
dynamics in a multi-scale architecture.
Background
Transport of water, dissolved chemicals, and heat are intimately linked in soils and they are an
important, often crucial aspect of many environmental issues like quantity and quality of groundwater,
irrigation and soil salinization, coupling of soil and atmosphere, and stability of permafrost soils.
Despite their acknowledged significance, these processes are hardly ever represented accurately and
with sufficient detail in models of environmental systems. The fundamental reason for this is that
their is a huge disparity between the scale at which the underlying physics is understood, typically
much less than one meter, and the scale at which a process representation is required for modeling
the environment, typically hundreds of meters to tens of kilometers. The same is true for other
environmental compartments like the atmosphere or the oceans. There, however, appropriate scaling
laws facilitate the closing of the gap for many processes. In terrestrial systems, this is prevented by
the multi-scale architecture of the medium.
A further challenge of terrestrial systems is the inherent and extreme nonlinearity. For instance,
the hydraulic conductivity depends strongly on water content and can easily vary by some 10 orders of
magnitude in a coarse-textured soil. Depending on the external forcing, such a range may be covered
within weeks or months during the summer dry-out or it is swept within minutes during a heavy
rainfall or flooding event.
With our research, we target both major issues: the local processes themselves and the efficient
and accurate determination of the multi-scale architecture.