Environmental Biogeochemistry

(c) Dr. Walter Schenkeveld

Environmental Biogeochemistry is an exciting field of research that studies how biotic (organisms) and abiotic parts (soil, minerals, natural organic material) of the environment chemically interact. These interactions control key processes in the environment such as the mobilization, transformation or stabilization 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 the protection against toxins. The nature of the chemistry involved is often complex and divers, and includes redox processes, acid base chemistry, dissolution and precipitation processes, and complexation reactions.The research of our group focuses on clearing up the chemical mechanisms employed by biota on the molecular scale and on quantitatively understanding them.

We do this in 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 Isotope 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. One 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. 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 multiple 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 to purify the samples prior to analysis.

The analysis of mercury (Hg) stable isotope signatures stands at the center 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.

Guidelines for MC-ICP-MS Laboratory

 

(c) Dr. Jan Wiederhold