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In freshwater ecosystems trace metals are mainly bound to and transported by natural organic matter (NOM) and different types of iron (Fe) colloids/particles. The chemical speciation of Fe, and also its interaction with NOM and metals, is largely controlled by the pH and redox level of the aqueous phase. Under oxidizing conditions, where Fe is present as Fe(III), the speciation is mainly controlled by a competition between precipitation as Fe(III)-(hydr)oxides and binding of Fe(III) to oxygen-containing groups in NOM. Under reducing conditions, where Fe(II) and free sulfides are present, there is an analogous competition between precipitation of FeS and binding of Fe(II,III) to NOM. In general, these processes are much better characterized in oxidizing than in reducing systems. Although it is known that the mobility/reactivity of trace metals in ecosystems to a large extent is controlled by interactions with Fe-phases and NOM, a more detailed process-oriented understanding is required, both on a fundamental molecular level and on an ecosystem/landscape level.

The Umeå Environmental and Biogeochemistry Initiative is one of Umeå University's strong research environments and we now announce two postdoctoral positions to expand our research on iron and natural organic matter as transporters of trace metals in aquatic systems. The overall strategic objective of the Initiative is to strengthen and further explore integrated research efforts and techniques for advanced research in environmental chemistry and biogeochemistry. We strive to promote advances in the quantitative and mechanistic understanding of biogeochemical cycles, which combine chemical-physical-biological processes over a range of temporal and spatial scales. Our current research environment offers outstanding prerequisites for joint research at the interface between environmental chemistry and ecosystem-oriented biogeochemistry. Both fundamental and more applied research are conducted, in collaboration with other universities and also with stakeholders outside academia. Preliminary, the two projects will be focused on one or several of the trace metal/metalloids mercury, cadmium, and arsenic.

Position 1 (ref nr 315-567-12)
Molecular level studies of Fe - NOM - trace metal interactions in controlled model systems

This project will concern fundamental studies on three-component interactions between Fe-NOM-trace metal(s) in controlled model systems. The project includes design and measurements on model systems and chemical modeling of the results. The studies will be focused on reduced systems where Fe is present as Fe(II) and precipitation of FeS can occur. Adsorption/desorption processes of trace metals to FeS/NOM systems will be studied, including binding mechanisms and characterization of complexes' coordination and stability constants. Understanding of these fundamental processes is crucial for understanding the biogeochemical cycling of trace metals at ecosystem/landscape levels, and the two proposed post-doc projects will therefore be closely integrated.

Experimental work in the laboratory will include the design and set up of relevant model systems with varying complexity and the use of various spectroscopic techniques for quantification of adsorbed and dissolved metals, and characterization of solid and aqueous phase speciation of metals. Relevant analytical techniques include inductively coupled plasma mass spectrometry, possibly with gas or liquid chromatography separations, spectroscopic techniques based on Fourier transform infrared and ultraviolet/visible spectroscopy, as well as synchrotron based X-ray absorption spectroscopy. Chemical speciation modeling will be used to further assess the speciation of dissolved metals.

Position 2 (ref nr 315-574-12)
Fe-NOM-trace metal interactions in aquatic ecosystems

This project will involve new innovative techniques with respect to chemical characterization of sedimenting material and sediments across redox gradients. The aim is to obtain molecular-level information about the chemical speciation of the main sediment constituents using various spectroscopic techniques for quantification of adsorbed and dissolved metals, and characterization of solid and aqueous phase speciation of metals. Relevant analytical techniques include wavelength-dispersive x-ray fluorescence spectrometry, inductively coupled plasma mass spectrometry, possibly with gas or liquid chromatography separations, spectroscopic techniques based on Fourier transform infrared and ultraviolet/visible spectroscopy, as well as synchrotron based X-ray absorption spectroscopy. This will open unique possibilities to interpret the redox status of the sediments as well as the coordination and chemical characteristics of elements such as Fe.

Samples will be collected from different lake environments at sites where on-going limnological and paleolimnological studies are underway. For example, in one of the study lakes, chemical speciation can be traced from soils via sediment traps to lake bottom, and across time in a series of sediment cores collected over the last few decades. Based upon the information provided by the analytical methods, chemical speciation models for the samples will be designed. These models will be used to discuss diagenetic processes and can also serve as predictive tools to foresee future changes in recent lake sediment geochemistry.

For both positions, the successful candidate should have a PhD in (bio)geochemistry, analytical chemistry or a closely related field, and demonstrated experience applying some of the listed analytical techniques. The degree should in the first case not be more than three years old. For position 2, experience from the analysis of natural environmental media (e.g., sediment, soils, seston) and from field sampling of soils and lake sediments is also considered meritorious.

For both positions we also demand a documented capability of autonomous scientific research work and skills in writing scientific publications and reports in English. In addition, the postdoctoral researcher is expected to participate in other current research projects within the collaborating research groups, and a willingness to develop research-funding possibilities within the research groups is encouraged. Very good command of the English language, both written and spoken, is required.

The positions are for full-time under two years. Your application should contain: (1) a cover letter summarizing your research accomplishments and how you could contribute to the research project, (2) a Curriculum Vitae, (3) a publication list, (4) transcripts of relevant degree certificates and publications, and (5) names and contact details of 2-3 references.

The application can be submitted either electronically or in hard-copy form. All documents submitted in hard-copy form should be in duplicate, and all electronically submitted material should be in MS Word or PDF format. Should you wish to apply for both positions, separate applications need to be submitted.

For further information, please contact:

For position 1 (315-567-12); Professor Per Persson (+46-(0)90-786 55 73, per.persson@chem.umu.se) or Associate professor Erik Björn (+46-(0)90-786 51 89, erik.bjorn@chem.umu.se).

For position 2 (315-574-12); Professor Richard Bindler (+46-(0)90-786 97 42, richard.bindler@emg.umu.se) or Associate professor Christian Bigler (+46-(0)90-786 97 29, christian.bigler@emg.umu.se).

Union information is available from SACO, +46-(0)90-786 53 65, SEKO, +46-(0)90-786 52 96 and ST, +46-(0)90-786 54 31. Your complete application, marked with correct reference number, should be sent to jobb@umu.se (state the reference number as subject) or to the Registrar, Umeå University, SE-901 87 Umeå, Sweden to arrive August 7, 2012 at the latest.