Countless geochemical and environmental processes occur
on the microscopic-scale. As such, a fundamental understanding of these
microscopic phenomena is necessary to understand the influence of these
processes on large-scale environments and ecosystems. I am interested in
the examination of these processes using spectroscopic techniques such as
X-ray absorption spectroscopy (XAS) and vibrational spectroscopies
including infrared and Raman spectroscopy. Specifically, my research can
be divided into three components, (1) chemically and biologically mediated
cycling of iron, sulfur, and associated trace metals; (2) mechanistic
investigations of mineral precipitation and surfaces; and (3) the use of
synchrotron-based spectroscopic techniques for the study of soil and
sediment processes.
To date, I have studied the chemical behavior of many
trace metals in both oxic and anoxic environments. For example, arsenic
and molybdenum partition strongly to sulfide minerals in anoxic soils and
sediments. I have examined arsenic and molybdenum speciation in sulfidic
sediments and the mechanism by which arsenic and molybdenum are retained
to better understand the behavior of arsenic in these anoxic environments.
Often simple adsorption processes are insufficient to describe trace metal
retention. Ternary complexes, the synergistic adsorption of ion pairs, may
facilitate adsorption; e.g., uranium(VI) forms phosphate ternary complexes
on iron oxides in some soils. Chemical processes (e.g., arsenate may be
reduced by manganese oxides) or biological processes (e.g., uranium
reduction by microorganisms) may reduce trace metals, potentially
influencing their bioavailability and/or transport properties. Redox
transformations may also indirectly influence trace element speciation.
Zinc is transformed to zinc sulfide (sphalerite) under reducing conditions
without changing its oxidation state. Consequently, I also work to
understand the processes that modulate iron and sulfur speciation in
soils, lake sediments, and within ocean particulate matter. These few
examples taken from my work and those of others illustrate the importance
of these individual processes that regulate the bioavailability and
transport of many elements. I am interested in continuing these
mechanistic studies, as well as the study of both pristine and
contaminated environments to better understand the fundamental geochemical
and biogeochemical processes.
