『Abstract
This study used batch reactors to characterize the mechanisms
and rates of elemental release (Al, Ca, K, Mg, Na, F, Fe, P, Sr,
and Si) during interaction of a single bacterial species (Burkholderia
fungorum) with granite at T = 28℃ for 35 days.The objective
was to evaluate how actively metabolizing heterotrophic bacteria
might influence granite weathering on the conditions. We supplied
glucose as a C source, either NH4 or NO3 as H sources, and either dissolved PO4
or trace apatite in granite as P sources. Cell growth occurred
under all experimental conditions. However, solution pH decreased
from 〜7 to 4 in NH4-bearing reactors, whereas
pH remained near-neutral in NO3-bearing reactors.
Measurements of dissolved CO2 and gluconate
together with mass-balances for cell growth suggest that pH lowering
in NH4-bearing reactors resulted from gluconic
acid release and H+ extrusion during NH4
uptake. In NO3-bearing reactors, B. Fungormum
likely produced gluconic acid and consumed H+ simultaneously
during NO3 utilization.
Over the entire 35-day period, NH4-bearing
biotic reactors yielded the highest release rates for all elements
considered. However, chemical analyses of biomass show that bacteria
scavenged Na,P, and Sr during growth. Abiotic control reactors
followed different reaction paths and experienced much lower elemental
release rates compared to biotic reactors. Because release rates
inversely correlate with pH, we conclude that proton-promoted
dissolution was the dominant reaction mechanism. Solute speciation
modeling indicates that formation of Al-F and Fe-F complexes in
biotic reactors may have enhanced mineral solubilities and release
rates by lowering Al and Fe activities,. Mass-balances further
reveal that Ca-bearing trace phases (calcite, fluorite, and fluorapatite)
provided most of the dissolved Ca, whereas more abundant phases
(plagioclase) contributed negligible amounts. Our findings imply
that during the incipient stages of granite weathering, heterotrophic
bacteria utilizing glucose and NH4 only moderately
elevate silicate weathering reactions that consume atmospheric
CO2. However, by enhancing the dissolution
of non-silicate, Ca-bearing trace minerals, they could contribute
to high Ca/Na ratios commonly observed in granitic watersheds.』
1. Introduction
2. Materials and method
2.1. Characterization and preparation o granite samples
2.2. Model microorganism and growth media
2.3. Batch experiments
2.4. Collection and preparation of cell biomass for chemical
analyses
2.5. Chemical analyses and data treatment
3. Results and discussion
3.1. Granite mineralogy and geochemistry
3.2. Glucose consumption, bacterial growth, and pH trends
3.3. Sources and acidity
3.4. Dissolved elemental concentrations
3.5. Elemental release rates
3.6. Elemental uptake by bacteria
3.7. Sources of dissolved Ca and effect on dissolved Ca/Na ratios
4. Conclusions and implications
Acknowledgments
References