ESD welcomes George W. Luther, Ph.D. (Univ. of Delaware)
The oxidation of aqueous Fe(II) to Fe(III) solids is of great significance to Earth history including banded iron formation (BIFs) and the rise of O2 in waters and the atmosphere. The chemical oxidation of aqueous Fe(II) in air saturated solutions is facile at circumneutral pH, but O2 arises mainly from photosynthetic activity. There are currently three theories on how microbes could have contributed to Fe(III) precipitation: (1) oxygenic photosynthesis, coupled to abiotic Fe oxidation, (2) aerobic (anerobic?) Fe oxidation by iron oxidizing bacteria (FeOB), and (3) anoxygenic photosynthesis, with Fe as an electron donor (photoferrotrophs). Using kinetic data obtained in the field as well as in the laboratory with in situ microelectrode techniques developed in our lab, it is now possible to discriminate between chemical Fe(II) oxidation and these microbially based processes in real time. Field data will be shown from diverse sites including Yellowstone National Park where groundwater, rich in Fe(II) and Mn(II) but with little or no O2, enter oxygenated systems. In the case of FeOB, their importance in Fe(II) oxidation increases at low O2 concentrations. Thermodynamic calculations for the first electron transfer between the metal ions, Fe(II) and Mn(II),with O2 over pH gives insight to the distribution of these metals in BIFs and their biogeochemical behavior.
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