Samuel, Ashley Laura. Investigating geophysical signatures of long term biodegradation at the oil spill site in Bemidji, Minnesota. Retrieved from https://doi.org/doi:10.7282/T3GB26C2
DescriptionBiogeophysics is a sub-discipline of geophysics that examines how microbial interactions with geologic materials affect the geophysical signatures within the subsurface. Biogeophysical measurements were performed at the National Crude Oil Spill Fate and Natural Attenuation Research Site in Bemidji, Minnesota where biodegradation of hydrocarbon contaminants is occurring. Geophysical measurements were acquired to ascertain whether changes in the pore fluid conductivity and/or the production of secondary iron minerals such as magnetite affect geophysical signatures at this site. The effects of hydrology, geology, oil levels and temperature on geophysical signatures within both an uncontaminated zone and a biodegraded contaminated zone were investigated. Resistivity, time domain induced polarization and frequency domain induced polarization measurements were acquired from a contaminated location and an uncontaminated location at the site. Results of this study suggests that the changes in the pore fluid conductivity primarily control the geophysical signatures when compared to the effects of the formation of magnetite within the smear zone in the contaminated zone. Hydrology, oil levels and temperature do not appear to explain the geophysical signatures from the contaminated location, although natural water table variations can explain the resistivity variations at the uncontaminated location. This study demonstrates that geophysical methods can be used to assist in the monitoring of the long term changes in geophysical signatures due to natural attenuation processes associated with biodegradation of a crude oil spill.