Investigating geophysical signatures of microbial cells, processes, and degradation: Implications for the geophysical monitoring of microbial activity and degradation in the subsurface

An integral part of soil remediation is the efficient monitoring of geochemical and microbial processes in the subsurface. The shallow subsurface environment is a dynamic system undergoing continuous change. The chemical and physical properties are affected by natural processes and by anthropogenic impacts, especially in the case of contaminated soils. Subsurface monitoring is hindered by our inability to directly observe any geochemical or microbiological process in real time and in situ.; High resolution geophysical methods can be used for efficient shallow subsurface monitoring in real time and with high spatial variability. I investigated the use of common geophysical methods to detect and/or monitor microbial cells, microbial processes, and degradation in the subsurface.; In chapter 2, I investigate the use of geoelectrical methods to monitor microbial presence within a simple system. Real and imaginary conductivity measurements are associated with the presence of metabolically inactive but alive microbial cells in sand media. Imaginary conductivity appears to be very sensitive in cell density changes whereas the real conductivity is not affected. The limitations of the method and possible mechanisms are discussed.; In chapter 3, I investigate the use of geoelectrical methods to detect and monitor metal sulfide mineralization due to microbial activity. Imaginary conductivity changes are coupled with metal - fluid interfacial area changes and the biomineral formation. The mineral precipitants structure and aging influence both imaginary and real conductivity. This study shows the potential of geoelectrical methods to monitor microbial processes involving sequestration of heavy metals as insoluble precipitants.; In chapter 4, the self potential method is used as a method to monitor abiotic DNAPL degradation. Geochemical monitoring indicated that DNAPL degradation is intensified due to HgCl2 presence in abiotic columns; the SP measurements are sensitive to these degradation processes. A conceptual model for the SP source mechanism due to DNAPL degradation is proposed and implications for DNAPL monitoring are discussed.; Finally, in chapter 5 the research goals are summarized and addressed. The limitations and the advantages of geophysical methods to monitor remediation processes are discussed and future research is suggested.