Minerals Associated with Biofilms Occurring on Exposed Rock in a Granitic Underground Research Laboratory

Abstract

The concept of disposal of nuclear fuel waste in crystalline rock requires the effects of microbial action to be investigated. The Underground Research Laboratory excavated in a pluton of the Canadian Shield provides a unique opportunity to study these effects. Three biofilms kept moist by seepage through fractures in granitic rock faces of the Underground Research Laboratory have been examined. The biofilms contained a variety of gram-negative and gram-positive morphotypes held together by an organic extracellular matrix. Nutrient levels in the groundwater were low, but energy-dispersive X-ray spectroscopy has shown biogeochemical immobilization of several elements in the biofilms; some of these elements were concentrated from extremely dilute environmental concentrations, and all elements were chemically complexed together to form amorphous or crystalline fine-grained minerals. These were seen by transmission electron microscopy to be both associated with the surfaces of the bacteria and scattered throughout the extracellular matrix, suggesting their de novo development through bacterial surface-mediated nucleation. The biofilm consortia are thought to concentrate elements both by passive sorption and by energy metabolism. By Mossbauer spectroscopy and X-ray diffraction, one of the biofilms showed that iron was both oxidized and precipitated as ferrihydrite or hematite aerobically and reduced and precipitated as siderite anaerobically. We believe that some Archean banded-iron formations could have been formed in a manner similar to this, as it would explain the deposition of hematite and siderite in close proximity. This biogeochemical development of minerals may also affect the transport of material in waste disposal sites.

Unsaturated flow through a fracture–matrix network: Dynamic preferential pathways in mesoscale laboratory experiments

“…There is also evidence that within networks, fracture coatings and the erosion and mobilization of fillings can create situations where the physical and chemical domain of the network may be changing in time [e.g., Weisbrod et al, 1999]. Additionally, ever present microbial activity can lead to the formation of biofilms that may clog or alter pathways [e.g., Brown et al, 1994] as well as a time varying release of surface active chemicals [e.g., Totsche et al, 1997]. In combination with boundary conditions often driven by weather, flow within unsaturated, fractured rock remains a topic of considerable uncertainty.…”

Degradation of 2,4,6-tribromophenol by bacterial cells attached to chalk collected from a contaminated aquifer

“…Introducing pollutant-degrading micro-organisms into the contaminated area is an alternative technology that may allow rapid removal of the contaminants (Alexander 1999). Biodegradative activity of the introduced bacteria depends on the environmental factors prevailing at the site and the nature of the interaction between the bacteria and the matrix (Scholl et al 1990;Brown et al 1994). Data on the interaction between fractured chalk and organic matter indicate that contaminants can be adsorbed or diffused into the chalk matrix (Wefer-Roehl et al 2001).…”

Liquid phase structure within an unsaturated fracture network beneath a surface infiltration event: Field experiment

“…The surfaces of fractures are subject to alteration due to: mineralogic weathering, erosion [e.g., Weisbrod et al, 1998Weisbrod et al, , 1999Weisbrod et al, , 2000a, Copyright 2002 by the American Geophysical Union. 0043-1397/02/2000WR000167 deposition/dissolution [e.g., Bekri et al, 1997;Hanna and Rajaram, 1998;Weisbrod et al, 2000b], and biofilm development [e.g., Brown et al, 1994]; furthermore, geometry of the entire network may shift with temporal changes in the stress field [e.g., National Research Council, 1996]. Whatever the void space or surface chemistry within an unsaturated fractured rock mass, phase structure within that void space will control flow and transport.…”