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Iron Cycling In Microbially Mediated Acid Mine Drainage Derived Sediments

Leitholf, Andrew M
http://rave.ohiolink.edu/etdc/view?acc_num=akron1434976163

Abstract Details

2015, Master of Science, University of Akron, Geology.
Throughout the Appalachian region, active and historic coal mining exposes sulfide minerals to microbial and abiotic weathering. These processes dissolve minerals such as pyrite, creating soluble iron(II) and sulfuric acid. The acidic fluid, termed acid mine drainage (AMD), pollutes local waterways and can form large mounds of insoluble iron(III) phases (referred to as “iron mounds”), through a series of biologically mediated processes. Iron mounds are generally composed of a variety of iron(III) (hydroxy-) oxide minerals that are metabolized by microbes. The microbially mediated processes of interest in AMD rely on iron(II) and iron(III). Conversion between these two oxidation states requires reduction or oxidation (redox) reactions to occur. this transfer of electrons may result in generation of an electric potential (EP) measured in volts. The generation of EP has previously been linked to abiotic processes, but recently has been noted to result from a variety of microbiological processes. The three goals of this study were to 1) determine whether EP signals could be linked to microbial activity within an iron mound setting 2) to determine whether electrochemical signals generated by microbial activity could be distinguished from abiotic redox processes, and 3) to establish whether EP in non-sterile sediments would correlate specifically to microbially mediated iron cycling. To accomplish these goals, iron mound sediment columns were incubated to permit the investigation of EP via voltage measurements against a Ag-AgCl reference, iron(II) accumulation was measured in pore fluid, along with dissolved oxygen (DO), and pH. By monitoring these electrochemical signals it was possible to delineate regions of microbial activity. Using the collected data, a simple model was created using the Nernst equation to account for the iron(II)-iron(III) redox couple. Iron(II) was found to increase with depth in biologically active trials while iron(II) showed no change in abiotic control incubations. Changes in EP with depth reflected the establishment of a redox gradient within the sediment column. EP initially reflected changes in iron(II) concentration, but after the initial 10 days EP ceased tracking iron(II) accumulation. Changes in EP were not significantly different between incubations under oxic and anoxic conditions, indicating similar processes are likely occurring regardless of oxygen availability. From these results it was concluded that the patterns of EP and iron(II) accumulation were demonstrably different between non-sterile sediment and sediment which had been biologically deactivated. In non-sterile sediments, EP and iron(II) were linked to a redox gradient that was established between -18 and -66 mm from the fluid-sediment interface. The depth dependent nature of iron(II) accumulation, behavior of EP with depth, similarity between microbially non-sterile trials, and emergence of a redox gradient within the non-sterile columns may be explained by extra-cellular electron transfer (EET). A simple model based on the Nernst equation, was used to attempt to describe EET within the column. It was successful in matching EP signal shape but did not fully account for the magnitude of observed EP.
John Senko, Dr. (Advisor)
Hazel Barton, Dr. (Committee Member)
David Steer, Dr. (Committee Member)
80 p.
Environmental Geology; Geobiology; Geochemistry; Geophysical; Hydrologic Sciences
Electro-chemistry; Acid Mine Drainage; Python; Geomicrobiology; Electric Potential; Iron cycling; Redox; Aqueous Geochemistry; Appalachia; Iron Mound

Recommended Citations

Citations

  • Leitholf, A. M. (2015). Iron Cycling In Microbially Mediated Acid Mine Drainage Derived Sediments [Master's thesis, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1434976163

    APA Style (7th edition)

  • Leitholf, Andrew. Iron Cycling In Microbially Mediated Acid Mine Drainage Derived Sediments. 2015. University of Akron, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1434976163.

    MLA Style (8th edition)

  • Leitholf, Andrew. "Iron Cycling In Microbially Mediated Acid Mine Drainage Derived Sediments." Master's thesis, University of Akron, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1434976163

    Chicago Manual of Style (17th edition)

akron1434976163
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This open access ETD is published by University of Akron and OhioLINK.