| dc.description.abstracteng | The presented thesis is of pronounced interdisciplinary character; based on applied physics, it addresses a challenging analytical task in soil science.
The goal of this work is to specify and analyze the sulfur pool of urban soils with major anthropogenic impact, i.e. the dumping of war debris. This impact obviously influences soil composition and soil formation processes, but may, due to sulfate leaching, also be a substantial risk to urban water quality. Therefore, the sulfur load of different debris components was studied and the sulfur content of different soil samples was evaluated and correlated to different parameters, such as position of the respective soil horizon within the soil profile or location of the soil profile in the surrounding terrain.
In terms of methods, the goal of this work is to show that x-ray absorption spectroscopy and x-ray microscopy are highly suitable to address the analytical problem of sulfur speciation in complex soil samples. Two major advantages are important to stress at this point: (a) the capability to differentiate the occurring oxidation states of sulfur (speciation) and (b) the capability to combine spectroscopy with spatial resolution on the micron and sub-micron scale in terms of spectromicroscopy.
An important part of this work was to evaluate under which experimental parameters and in combination with which data analysis method x-ray absorption spectroscopy of sulfur in urban soil samples can be carried out optimally.
The following modalities of x-ray absorption spectroscopy were used: sulfur K-edge XANES spectroscopy, x-ray microscopy in terms of x-ray fluorescence imaging, and a combination of both, x-ray spectromicroscopy.
With pure XANES spectroscopy, the averaged sulfur pool of whole soil horizons as well as of single debris components was studied, applying different data analysis methods. These are peak fitting, principle component analysis (PCA), and linear combination fitting (LCF). Each of the methods gives particular insight into different sample properties, that may be mutually adaptable or complementary. PCA (when considering target transformation) and LCF are crucially dependent on an appropriate database of standard spectra.
With x-ray fluorescence imaging and spectromicroscopy, soil aggregates, debris particles, and soil solution were analyzed on the micrometer scale. These measurements show highly heterogeneous sample composition and clear gradients in sulfur speciation and oxidation state within single particles. The weathering of the anthropogenic material is therefore directly observable.
This work demonstrates the general applicability of sulfur x-ray spectroscopy and spectromicroscopy to analytical problems in urban soils. It also addresses the proper sample preparation techniques.
This work was supported by the DFG under contract number TH 445/11-1, AOBJ: 552902: ''Mechanismen der Sulfatfreisetzung aus Trümmerschuttböden'', which was a joint project of the working groups of Dr. Jürgen Thieme, Institute for X-Ray Physics, University of Göttingen (affiliation when the project started) and Prof. Dr. Gerd Wessolek, Department of Ecology, Technical University Berlin. | de |