Notes: Two detailed vertical profiles through a complex plume of phenolic contaminants in a Triassic sandstone aquifer show that natural attenuation by biodegradation and dispersion is active but very slow. The plume has a microbially active aerobic and NO3 reducing fringe that is less than 2 m thick at both 150 and 350 m downstream of the source. The anaerobic core has evidence of active bacterial populations and degradation at total organic carbon (TOC) concentrations up to at least 1400 mg/L (1800 mg/L total phenolics), although gross half-lives are more than 50 years. There is evidence from the same locations of Mn, Fe, and SO4 reduction, with the latter inhibited by the pollutant matrix and not significant at concentrations more than 1000 mg/L TOC. Degradation of these contaminants in this aquifer is influenced by a range of environmental factors, including the chemical toxicity and pH of the contaminant matrix, and inputs of electron acceptors into the plume by dispersion. The results show that the plume is likely to grow under the present conditions, despite the biodegradable nature of the organic pollutants and availability of suitable electron acceptors. Vertical profiles have proved a cost-effective method of understanding the evolution of the plume.

Notes: Silicified deposits, such as sinters, occur in several modern geothermal environments, but the mechanisms of silicification (and crucially the role of microorganisms in their construction) are still largely unresolved. Detailed examination of siliceous sinter, in particular sections of microstromatolites growing at the Krisuvik hot spring, Iceland, reveals that biomineralization contributes a major component to the overall structure, with approximately half the sinter thickness attributed to silicified microorganisms. Almost all microorganisms observed under the scanning electron microscope (SEM) are mineralized, with epicellular silica ranging in thickness from 〈 5 μm coatings on individual cells, to regions where entire colonies are cemented together in an amorphous silica matrix tens of micrometres thick. Within the overall profile, there appears to be two very distinct types of laminae that alternate repeatedly throughout the microstromatolite: ‘microbial’ layers are predominantly consisting of filamentous, intact, vertically aligned, biomineralized cyanobacteria, identified as Calothrix and Fischerella sp.; and weakly laminated silica layers which appear to be devoid of any microbial component. The microbial layers commonly have a sharply defined base, overlying the weakly laminated silica, and a gradational upper surface merging into the weakly laminated silica. These cyclic laminations are probably explained by variations in microbial activity. Active growth during spring/summer allows the microorganisms to keep pace with silicification, with the cell surfaces facilitating silicification, while during their natural slow growth phase in the dark autumn/winter months silicification exceeds the bacteria’s ability to compensate (i.e. grow upwards). At this stage, the microbial colony is probably not essential to microstromatolite formation, with silicification presumably occurring abiogenically. When conditions once again become favourable for growth, recolonization of the solid silica surface by free-living bacteria occurs: cell motility is not responsible for the laminations. We have also observed that microbial populations within the microstromatolite, some several mm in depth, appear viable, i.e. they still have their pigmentation, the trichomes are not collapsed, cell walls are unbroken, cytoplasm is still present and they proved culturable. This suggests that the bulk of silicification occurred rapidly, probably while the cells were still alive. Surprisingly, however, measurements of light transmittance through sections of the microstromatolite revealed that photosynthetically active light (PAL) only transmitted through the uppermost 2 mm. Therefore the ‘deeper’ microbial populations must have either: (i) altered their metabolic pathways; (ii) become metabolically inactive; or (iii) the deeper populations may be dominated by different microbial assemblages from that of the surface. From these collective observations, it now seems unequivocal that microstromatolite formation is intimately linked to microbial activity and that the sinter fabric results from a combination of biomineralization, cell growth and recolonization. Furthermore, the similarities in morphology and microbial component to some Precambrian stromatolites, preserved in primary chert, suggests that we may be witnessing contemporaneous biomineralization processes and growth patterns analogous to those of the early Earth.

Notes: The spontaneous precipitation of amorphous iron hydroxide and ferric hydroxysulfate has generally been considered to be an inorganic process involving the oxidation of ferrous iron with or without the presence of sulfate. However, our study of bacterial communities growing in an acid mine drainage lagoon sediment has confirmed that microorganisms were also capable of facilitating this mineral precipitation. Transmission electron microscopy revealed that bacteria growing at the surface had iron-rich capsules, along with detectable amounts of Zn, Ti, Mn and K incorporated into the mineralised matrix. In the subsurface, more cells were associated with granular, fine-grained mineral precipitates, composed almost exclusively of iron and sulfur. Pore water profiles indicated that no discernible sulfate reduction had taken place, suggesting that these authigenic minerals were ‘ferric hydroxysulfate’, and not iron sulfide. Energy dispersive X-ray spectroscopy further indicated that the subsurface minerals had variable composition, with the Fe:S ratio decreasing with depth from 3.5:1 at 15 cm to 1.9:1 at 30 cm. This indicates the high reactivity of ferric hydroxide for dissolved sulfate. Because iron reduction was limited to sediment depths between 3–10 cm, it is conceivable that these minerals are not amenable to bacterial reduction, and hence, the ability of bacteria to bind and form such precipitates may provide a natural solution to cleansing acidified waters with a high dissolved metal content.

Notes: [Auszug] YARDLEY ET AL. REPLY - The differences between our interpretation of regional fluid flow through the Connemara marble and Tanner's arise through differences in our maps; oversimplifications that inevitably accompany a short article; and because of differences in interpretation of the relative ...

Notes: [Auszug] The area investigated is in Connemara, western Ireland, where a late Precambrian (Dalradian) succession of sediments has undergone a complex history of folding and metamorphism8, culminating in a low-pressure, high-temperature metamorphism with accompanying folding (D3) that was related to the ...

Notes: Abstract Erosion of the Edale shales of Derbyshire during the Tertiary and Quaternary has resulted in sediment deposits in and on the underlying karstified limestones. Sorting during sedimentation has generated clay-rich sediments which are uranium enriched due to a clay association of uranium in the shales. Radon production in these sediments is at or close to equilibrium with their uranium content, and their fine grain-size ensures efficient radon release. Such sediments are therefore potent local sources of environmental radon.