The stable isotope signature of pore water provides an integral fingerprint of water origin, flow path, transport processes, and residence time and can thus serve as a powerful tracer of vadose zone hydrological processes. However, the full potential of stable isotopes to quantitatively characterize vadose zone water dynamics under varying conditions is yet unfolded. A major reason is the difficulty in obtaining continuous in-situ measurements of spatiotemporally variable stable isotope signatures of pore water. Using a field-deployable laser-based isotope analyzer, a new non-destructive and fully automatable sampling system for the continuous in-situ sampling of the stable isotope signature of pore water was recently developed at the Chair of Hydrology and successfully applied in field experiments during the summer of 2012. This technique provides a innovative tool to investigate water dynamics, input and output fluxes as well as stable isotope behavior in soils. However, several aspects of liquid and gaseous soil water stable isotope behavior important to in-situ measurements are still unknown and urgently require detailed investigation.

The goal of this thesis is to investigate the effects of different soil physical properties and states - including soil water content, matric potential, and temperature - on stable isotope signatures in the liquid and vapor phase of soils related to the in-situ measurement of stable isotope signatures of pore water. This shall enhance both our physicochemical understanding of the processes involved and our ability to measure the stable isotope signature of soil water in-situ with high accuracy and precision.

The thesis work will include planning, execution, and evaluation of suitable lab experiments to achieve the defined goal. This involves the application of the newly developed sampling system, including a laser-based isotope analyzer, in soil column and/or soil core experiments. The generated data will then be analyzed and interpreted to understand the observed behavior and establish quantitative relationships between the soil physical properties and states of interest and the stable isotope signatures derived by in-situ sampling.

Markus Weiler und Till Volkmann

The work involves laboratory (and field) experiments and may involve collection of suitable soil material in the vicinity of Freiburg.

Markus Weiler markus.weiler@hydrology.uni-freiburg.de Tel. +49 (0)761 / 203-3530

Stable Isotope Hydrology; Soil Hydrology; Laboratory Experimentation; Data Analysis

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