Dennis M. Lavoie

The role of biomineralization in microbiologically influenced corrosion

Synthetic iron oxides (goethite, α-FeO·OH; hematite, Fe2O3; and ferrihydrite, Fe(OH)3) were used as model compounds to simulate the mineralogy of surface films on carbon steel. Dissolution of these oxides exposed to pure cultures of the metal-reducing bacterium, Shewanella putrefaciens, was followed by direct atomic absorption spectroscopy measurement of ferrous iron coupled with microscopic analyses using confocal laser scanning and environmental scanning electron microscopies. During an 8-day exposure the organism colonized mineral surfaces and reduced solid ferric oxides to soluble ferrous ions. Elemental composition, as monitored by energy dispersive x-ray spectroscopy, indicated mineral replacement reactions with both ferrihydrite and goethite as iron reduction occurred. When carbon steel electrodes were exposed to S. putrefaciens, microbiologically influenced corrosion was demonstrated electrochemically and microscopically.

Fundamental response of pore-water pressure to microfabric and permeability characteristics: Eckernförde Bay

Ambient and dynamic in situ pore pressures were measured, and microfabric was examined in finegrained, shallow-water sediment in Eckernförde Bay, Germany. In situ permeabilities were calculated from piezometer data. Pore-water pressure decay times in sediments 0.5–1.0 m subbottom are indicative of clayey materials. Shallower sediments, although of similar classical grain size as the deeper sediments, have quicker decay times typical of silty marine sediment. Pore pressure response is a function of the microfabric, porometry, and sediment permeability. Aggregates (composed of fine-grained material, biota, and extracellular polymers) produce large pores and complex microstructure, resulting in effective permeabilities characteristic of silts.

Environmental Scanning Electron-Microscopy of Marine Aggregates

Marine aggregates were examined for the first time in the hydrated state using an environmental scanning electron microscope (ESEM). Sample preparation consisted of fixation followed by rinsing with distilled water to remove excess salts and fixative. Aggregates were continuously observed at resolutions comparable to conventional scanning electron microscopy through stages of hydration, from completely immersed to desiccated. Because no metallic coating is required, energy‐dispersive X‐ray spectroscopy (EDXS) can be used to analyse rapidly constituent elements occurring at low concentrations with no spectral interference. Subtle differences in mineral particles were seen in both EDXS spectra and in direct observation of relative hydration, reflecting apparent differences in mineralogy. ESEM enabled examination of effects of desiccation and rehydration on individual particles composed primarily of hydrated polymer and eliminated dehydration artefacts in delicate organisms.

Bulk sediment properties interpreted in light of qualitative and quantitative microfabric analysis

Sediments from Eckernförde Bay, Germany, are characterized by an aggregate and channel microstructure, with channel dimensions about two orders of magnitude larger than interparticle distances within aggregates. Porosity within aggregates as determined by image analysis of transmission electron micrographs was about 12% less than bulk porosity. Illite and smectite formed the bulk of most aggregates, while numerous biogenic particles generally occurred outside or on the periphery of aggregates. Microfabric analysis provides insights into permeability and consolidometer behavior of this sediment, reveals characteristics not apparent from bulk analyses, and may have implications for geochemistry and physical behavior of the sediment.