BIOGEOPHYSICS

Mentor: Prof. R.G.S. Sastry

Students:

Aarti Dwivedi

Vedbrat

What is it?

The use of geophysical techniques to measure not simply the physical and chemical properties of the subsurface, as already well established, but also to detect microbes, microbial growth, and microbe-mineral interactions.

A REVIEW OF MAJOR WORK DONE IN THE LAST DECADE IN BIOGEOPHYSICS

Most prominent authors:

E. ATEKWANA

Biogeophysics: A New Frontier in Earth Science Research

This paper introduces the concept of biogeophysics, how geophysics can help in detection of microbes and the properties of microbes that makes it possible for geophysical methods to be used in this case. Major properties are: biofilm, metabolic byproducts, redox processes, magnetotactic bacteria. It tells about biogeochemical transformations like microbe mediated reactions. It proposes the studies of deep ocean, cryosphere, extraterrestrial life using biogeophysics.

Acoustic and electrical property changes due to microbial growth and biofilm formation in porous media

This paper explains about a laboratory study that was conducted to investigate the effect of microbial growth and biofilm formation on compressional waves, and complex conductivity during stimulated microbial growth. It discusses the temporal variability of complex conductivity, spatial variability of acoustic properties and effect of biofilm structure and development on acoustic properties.

The Microbial Community Structure in Petroleum-Contaminated Sediments Corresponds to Geophysical Signatures

This paper suggests the use of geoelectrical measurements as a cost-efficient tool to guide microbiological sampling for microbial ecology studies during the monitoring of natural or engineered bioremediation processes as changes in the geophysical properties of contaminated sediments

parallel changes in the microbial community compositions.

Evidence for microbial enhanced electrical conductivity in hydrocarbon

contaminated sediments

Bulk electrical conductivity of sediments during microbial mineralization of diesel was investigated in a mesoscale laboratory experiment consisting of biotic

contaminated and uncontaminated columns. This study suggests that geophysical methodologies may potentially be used to investigate microbial activity.

Sensitivity of geoelectrical measurements to the presence

of bacteria in porous media

The study showed a correlation between imaginary conductivity and microbial concentration. It reports the low frequency electrical response to measure density of cells and distinction between live and dead cells.

Geophysical Signatures of Microbial Activity

at Hydrocarbon Contaminated Sites: A Review

This paper suggests that microbial processes alter the contaminated environment causing changes in the petrophysical properties, solute concentration of pore fluids, and temperature. Geophysical techniques such as electrical resistivity, induced polarization, electromagnetic induction, ground penetrating radar, and self potential can define the contaminated zones because of the new physical properties imparted by microbial processes. The changes in the physical properties of the contaminated environment vary spatially because microbial processes depend on the spatial distribution of the contaminant.

LEE SLATER

A state space Bayesian framework for estimating biogeochemical transformations using timelapse geophysical data

This paper develops a state-space Bayesian framework to combine time-lapse geophysical data with other types of information for quantitative estimation of biogeochemical

parameters during bioremediation. A petrophysical model based on sphere-shaped cells to link the sulfide precipitate properties to the time-lapse geophysical

attributes and for estimating volume and fraction of precipitates, their dispersion, distribution of bacteria.

Porescale spectral induced polarization signatures associated with FeS biomineral
transformations

The low-frequency (0.1–10 Hz peak) relaxations produced during biomineralization is modeled with a Cole-Cole formulation, from which the evolution of the polarization magnitude and relaxation length scale can be estimated. It concludes that SIP signatures are diagnostic of pore-scale geometrical changes associated with FeS biomineralization by sulfate reducing bacteria.

Spectral induced polarization and electrodic potential monitoring of microbially
mediated iron sulfide transformations

SIP model parameters based on a ColeCole relaxation model of the polarization at the mineralfluid interface were converted to estimated biomineral surface area to pore volume(Sp), and an equivalent polarizable sphere diameter(d) controlling the relaxation time. A laboratory column experiments to investigate the geoelectrical response of iron sulfide transformations by Desulfovibrio vulgaris was conducted. Spectral induced polarization (SIP), and electrodic potential measurements, were used for investigation.

ANDRE REVIL

Magnetic susceptibility as a proxy for investigating microbially mediated iron reduction

This work investigates MS variations in a hydrocarbon

contaminated aquifer where methanogenesis and iron‐reduction are the main terminal electron acceptor processes. Results suggest enhancements in MS are due to the precipitation of magnetite coupled to iron‐reduction as related to anaerobic oxidation of hydrocarbon compounds within the smear zone and aerobic or anaerobic oxidation of methane within the vadose zone, which provides additional field evidence linking anaerobic oxidation of methane to iron‐reduction and suggests significant implications for methane cycling in terrestrial environments.

A new model for the spectral induced polarization signature
of bacterial growth in porous media

This work develops a quantitative model to investigate the frequency domain induced polarization response of suspensions of bacteria and bacteria growth in porous media. It shows that the growth rate and endogenous decay

coefficients of bacteria in a porous sand can be inferred non-intrusively from time-lapse frequency domain induced polarization data.

CHI ZHANG

Complex Dielectric Properties of Sulfate-Reducing

Bacteria Suspensions

This work showed that higher dielectric responses (relative dielectric permittivity, real and imaginary conductivity) occurred with higher bacteria concentration at frequencies<10 kHz. Additionally, permittivity and conductivity both decreased as cells aged from mid-log

phase to late stationary phase.

Improving Interpretation of geoelectrical signatures arising from biomineralization process in porous media: Low frequency dielectric spectroscopy measurements on Desulfovibrio vulgaris cell suspensions

This work studied low frequency dielectric properties of sulfate-reducing bacteria. The results provide insights into the likely contribution of the cells themselves to biogeophysical signals observed during biomineralization processes.

Monitoring microbial sulfate reduction in porous media using multipurpose
electrodes

In this study, reactive electrode measurements were combined to electrical geophysical measurements during microbial sulfate reduction occurring in a column of silica beads saturated with natural river water. Electrodic potential (EP), self potential (SP) and complex conductivity signals were recorded.The results suggest that the implementation of multipurpose electrodes, combining reactive measurements with electrical geophysical measurements, could improve efforts to monitor

microbial processes in the Earth using electrodes.