Does the presence of heterotrophic bacterium Pseudomonas reactans affect basaltic glass dissolution rates?

Far-from-equilibrium steady-state basaltic glass dissolution rates were measured using newly developed Bacterial Mixed-Flow Reactors (BMFR) at 25 degrees C. Experiments were performed in aqueous pH 4, 6, 8, and 10 buffer solutions with and without nutrients and in: 1) the absence of bacteria, 2) the presence of 0.1-0.4 g(wet)/L dead Pseudomonas reactans, and 3) in the presence of 0.9-19.0 g(wet)/L live P. reactans extracted from a deep subsurface oxygen-bearing basaltic aquifer. The BMFR allows steady-state rate measurements at constant concentrations of live or dead bacteria. Experiments ran for 30-60 days on a single basaltic glass powder, initially at bacteria- and nutrient-free conditions until Si steady-state glass dissolution was achieved. Then, in 2-4 steps, either live or dead P. reactans were added via nutrient-rich or nutrient-free inlet solutions, and the flux of Si and other mineral constituents from the basaltic glass were measured until a new chemical steady state was attained. Scanning Electron Microscope and X-ray Photoelectron Spectroscopic techniques verified the presence of live bacteria on the basaltic glass surfaces through biofilm formation, bacterial dissolution imprints, and enrichment of surface layers in C and N. The presence of either live or dead P. reactans lowers constant pH steady-state basaltic glass dissolution rates by no more than similar to 0.5 log units which is close to combined analytical and experimental uncertainties of the experiments. The presence of bacteria did not cause any significant modification in trace element release rates from dissolving basaltic glass within the uncertainty of the measurements. Experiments in nutrient-rich solutions yielded close to stoichiometric release of all major elements from basaltic glass at pH 6-8 likely as a result of organic ligand complexation with aqueous Al and Fe, which would otherwise form hydroxy-precipitates. As the results of this work suggest, at most, a small inhibiting effect of live or dead P. reactans on basaltic glass dissolution rates, geochemical modeling of mineral reactivity in basaltic aquifers likely does not require explicit provision for the presence of heterotrophic bacteria on basaltic glass reactivity. (C) 2011 Elsevier B.V. All rights reserved.