Silicates, silicate weathering, and microbial ecology

Mineralogy, microbial ecology, and mineral weathering in the subsurface are an intimately linked biogeochemical system. Although bacteria have been im plicated indirectly in the accelerated weathering of minerals, it is not cl ear if this interaction is simply the coincidental result of microbial meta bolism, or if it represents a specific strategy offering the colonizing bac teria a competitive ecological advantage. Our studies provide evidence that silicate weathering by bacteria is sometimes driven by the nutrient requir ements of the microbial consortium, and therefore depends on the trace nutr ient content of each aquifer mineral. This occurrence was observed in reduc ing groundwaters where carbon is abundant but phosphate is scarce: here, ev en resistant feldspars are weathered rapidly. This suggests that the progre ssion of mineral weathering may be influenced by a mineral's nutritional po tential, with microorganisms destroying only beneficial minerals. The rock record, therefore, may contain a remnant mineralogy that reflects early mic robial destruction of biologically valuable minerals. leaving a residuum of "useless" minerals, where "value" depends on the organism, its metabolic n eeds, and the diagenetic environment. Conversely, the subsurface distributi on of microorganisms may, in part, be controlled by the mineralogy and by t he ability of an organism to take advantage of mineral-bound nutrients.