Prof. Dr. Stephan M. KRAEMER

  (c) Thomas Exel
University of Vienna
Professor of Environmental Geochemistry
Head Department of Environmental Geosciences
Vice Director Studies Environmental Geosciences
Vice Director Doctoral School VDS-MES
Josef-Holaubek-Platz 2
A-1090 Vienna
Phone: +43-1-4277-53463

A list of current research projects can be found here


Environmental biogeochemistry is an exciting field of research that studies how biotic (organisms) and abiotic parts (soil, minerals and natural organic material) of the environment interact chemically. These interactions control key processes in the environment such as the mobilisation, transformation or stabilisation of pollutant, mineral weathering and solute acquisition of natural waters and global element cycling. Organisms interact chemically with their surroundings for multiple reasons including the acquisition of nutrients, the generation of energy for metabolic processes and protection against toxins. The nature of the chemistry involved is often complex and diverse, including redox processes, acid base chemistry, dissolution and precipitation processes and complexation reactions. Our group research focuses on clearing up the chemical mechanisms employed by biota on a molecular scale and on quantitatively understanding them.

We do this via field studies and in controlled laboratory experiments, employing various analytical techniques as well as non-traditional isotope geochemistry. We investigate the reactivity of biogenic chemical compounds in model systems but we also involve microbial cultures and plants as well as complex soil systems and sediments. The results of these studies are used to construct quantitative thermodynamic and kinetic models that may serve to predict the effect of biogeochemical processes in complex environments.

Environmental Geochemistry

Constraining environmental and Earth system processes requires the identification and elucidation of complex processes on molecular to global scales. The stable isotope signature of an environmental sample contains valuable information about source materials and transformation processes, which have affected the sample during environmental cycling. Interpreting variations in the stable isotope composition of natural samples requires knowledge of fractionation factors and mechanisms for specific processes as well as data on the isotopic variability of different source materials.

We employ two main study approaches in our research activities in environmental isotope geochemistry: On the one hand, we conduct laboratory experiments on well-defined model systems to determine stable isotope fractionation factors and elucidate fractionation mechanisms of individual processes, and on the other hand, we study the variations of stable isotope signatures on samples collected in the field, encompassing both pristine natural ecosystems as well as sites affected by anthropogenic contamination.

Our research focuses on the stable isotope fractionation of metals which represents a relatively new but very promising area in geosciences and environmental sciences. Other than the “traditional” stable isotope systems (C, H, O, N, S) which are measured by gas source mass spectrometry, the stable isotope analysis of metals requires the application of multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). In our laboratory, we use a Nu Plasma II MC-ICP-MS to measure metal stable isotope ratios with very high precision. The associated clean-room laboratory allows the preparation of samples under metal-free conditions which is necessary to achieve low blank levels and purify the samples prior to analysis.

The analysis of mercury (Hg) stable isotope signatures stands at the centre of our current research. Mercury is a global pollutant element which undergoes complex biogeochemical cycling under different environmental conditions and which is heavily influenced by anthropogenic activities. We use Hg stable isotope signatures, consisting of both mass-dependent fractionation (MDF) and mass-independent fractionation (MIF) components, to trace sources and transformation processes during environmental Hg cycling with a focus on contaminated field systems.