Invited Lecture: Exploring Microbial Controls On Mineral Weathering

We have measured the effects of specific organic polymers, small organic acids, and metabolic byproducts on mineral dissolution rates and reaction stoichiometries to quantify field-based observations. Microbial-mineral interactions can be driven by metabolic need for elements such as phosphorus. Geochemical and mineralogical data suggest that in organo-phosphate-limited regions of weathering profiles, microbial activity correlates with enhanced apatite dissolution, suppression of secondary phosphate precipitation, and ultimately, dissolution of all phosphates. Microbial colonization is strongly localized by phosphate mineral surfaces. Enhanced apatite dissolution was demonstrated experimentally by comparing reaction rates in controls with rates in phosphate-limited heterotrophic cultures and abiotic experiments containing either acetate or oxalate. For silicates, microbial interactions can enhance or suppress weathering rates. We have shown that organisms can derive energy by catalysis of oxidation of Fe2+ liberated by olivine dissolution. However, the resulting increased Fe3+ in solution decreases the olivine dissolution rate compared to abiotic controls.