Geology topics

M. Thomas

Publications and source records attributed to M. Thomas.

3 recordsLinked to original sources

USGS2006

Isolation of viral haemorrhagic septicaemia virus from muskellunge, Esox masquinongy (Mitchill), in Lake St Clair, Michigan, USA reveals a new sublineage of the North American genotype

Viral haemorrhagic septicaemia virus (VHSV) was isolated from muskellunge, Esox masquinongy (Mitchill), caught from the NW portion of Lake St Clair, Michigan, USA in 2003. Affected fish exhibited congestion of internal organs; the inner wall of the swim bladder was thickened and contained numerous budding, fluid-filled vesicles. A virus was isolated using fish cell lines inoculated with a homogenate of kidney and spleen tissues from affected fish. Focal areas of cell rounding and granulation appeared as early as 24 h post-inoculation and expanded rapidly to destroy the entire cell sheet by 96 h. Electron microscopy revealed virions that were 170-180 nm in length by 60-70 nm in width having a bullet-shaped morphology typical of rhabdoviruses. The virus was confirmed as VHSV by reverse transcriptase-polymerase chain reaction. Sequence analysis of the entire nucleoprotein and glycoprotein genes revealed the virus was a member of the North American genotype of VHSV; however, the isolate was sufficiently distinct to be considered a separate sublineage, suggesting its origin may have been from marine species inhabiting the eastern coastal areas of the USA or Canada.

Michigan↗

USGS2000

Methyl-mercury degradation pathways: A comparison among three mercury impacted ecosystems

We examined microbial methylmercury (MeHg) degradation in sediment of the Florida Everglades, Carson River (NV), and San Carlos Creek (CA), three freshwater environments that differ in the extent and type of mercury contamination and sediment biogeochemistry. Degradation rate constant ( k deg ) values increased with total mercury (Hg t ) contamination both among and within ecosystems. The highest k deg 's (2.8−5.8 d - 1 ) were observed in San Carlos Creek, at acid mine drainage impacted sites immediately downstream of the former New Idria mercury mine, where Hg t ranged from 4.5 to 21.3 ppm (dry wt). A reductive degradation pathway (presumably mer -detoxification) dominated degradation at these sites, as indicated by the nearly exclusive production of 14 CH 4 from 14 C-MeHg, under both aerobic and anaerobic conditions. At the upstream control site, and in the less contaminated ecosystems (e.g. the Everglades), k deg 's were low (≤0.2 d - 1 ) and oxidative demethylation (OD) dominated degradation, as evident from 14 CO 2 production. k deg increased with microbial CH 4 production, organic content, and reduced sulfur in the Carson River system and increased with decreasing pH in San Carlos Creek. OD associated CO 2 production increased with pore-water SO 4 2- in Everglades samples but was not attributable to anaerobic methane oxidation, as has been previously proposed. This ecosystem comparison indicates that severely contaminated sediments tend to have microbial populations that actively degrade MeHg via mer -detoxification, whereas OD occurs in heavily contaminated sediments as well but dominates in those less contaminated.

Environmental Science & Technology↗

USGS2000

Formation of natural gas hydrates in marine sediments. Gas hydrate growth and stability conditioned by host sediment properties

The stability conditions of submarine gas hydrates (methane clathrates) are largely dictated by pressure, temperature, gas composition, and pore water salinity. However, the physical properties and surface chemistry of the host sediments also affect the thermodynamic state, growth kinetics, spatial distributions, and growth forms of clathrates. Our model presumes that gas hydrate behaves in a way analogous to ice in the pores of a freezing soil, where capillary forces influence the energy balance. Hydrate growth is inhibited within fine-grained sediments because of the excess internal phase pressure of small crystals with high surface curvature that coexist with liquid water in small pores. Therefore, the base of gas hydrate stability in a sequence of fine sediments is predicted by our model to occur at a lower temperature, and so nearer to the seabed than would be calculated from bulk thermodynamic equilibrium. The growth forms commonly observed in hydrate samples recovered from marine sediments (nodules, sheets, and lenses in muds; cements in sand and ash layers) can be explained by a requirement to minimize the excess of mechanical and surface energy in the system.

Conference Paper↗