(Special Issue: Geochemistry of Aqueous Systems
edited by Susan Stipp, Patrick Brady, K. Vala Ragnarsdottir, Laurent
Charlet)
Geochimica Et Cosmochimica Acta Vol. 63 (19-20) pp. 3247-3259
a,b S.A. Welch and aW.J. Ullman
a College of Marine Studies, University of Delaware, , Lewes,
Delaware 19958 , USA
bDepartment of Geology and
Geophysics, University of Wisconsin at Madison, Weeks Hall, , Madison, Wisconsin
53706, USA
The rate of Si release from dissolving bytownite feldspar in abiotic batch
reactors increased as temperatures increased from 5¡ to 35¡C. Metabolically
inert subsurface bacteria (bacteria in solution with no organic substrate) had
no apparent effect on dissolution rates over this temperature range. When
glucose was added to the microbial cultures, the bacteria responded by producing
gluconic acid, which catalyzed the dissolution reaction by both proton- and
ligand-promoted mechanisms. The metabolic production, excretion, and consumption
of gluconic acid in the course of glucose oxidation, and therefore, the degree
of microbial enhancement of mineral dissolution, depend on temperature. There
was little accumulation of gluconic acid and therefore, no significant
enhancement of mineral dissolution rates at 35¡C compared to the abiotic
controls. At 20¡C, gluconate accumulated in the experimental solutions only at
the beginning of the experiment and led to a twofold increase in dissolved Si
release compared to the controls, primarily by the ligand-promoted dissolution
mechanism. There was significant accumulation of gluconic acid in the 5¡C
experiment, which is reflected in a significant reduction in pH, leading to
20-fold increase in Si release, primarily attributable to the proton-promoted
dissolution mechanism. These results indicate that bacteria and microbial
metabolism can affect mineral dissolution rates in organic-rich, nutrient-poor
environments; the impact of microbial metabolism on aluminum silicate
dissolution rates may be greater at lower rather than at higher temperatures due
to the metabolic accumulation of dissolution-enhancing protons and ligands in
solution.
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