Fluctuation Analysis of Oxidation-Reduction Potential in Circumneutral pH Iron-Oxidizing Microbial Systems

The goal of this thesis was to assess the utility of using small-scale fluctuations in oxidation-reduction (redox) potential to distinguish microbial from chemical iron oxidation. Fluctuations in potential arise from the motion of particles in a fluid; measuring fluctuations is therefore a system-scale observable property of micro-scale chemical behaviour, as such particle motion constitutes diffusion. Fluctuations are described by the strength of their correlation, as measured by scaling exponents. A method for the calculation of scaling-exponents of long-range correlation in redox potential measurements was developed, including new instrumentation and the modification of an existing physiological processing algorithm for use with environmental microbiological data sets. Steady-state biological and chemical systems were compared, and scaling exponents calculated from each system were found to differ significantly. In a final study, a series of microcosms were used to determine the relationship between scaling exponent, measuring correlation strength, and oxidation rate. The biological systems are governed by the rate of reaction, while the chemical systems appear to be diffusion-controlled. Because in these systems, Fe(II) is a metabolite, redox potential can then be interpreted as a physically-constrained proxy for metabolic activity. This allows the characterization of biological activity in situ.Ph.D