Effect of Supplemental Electron Donors on the Microbial Reduction of Fe(III), Sulfate, and CO(2) in Coal Mining-Impacted Freshwater Lake Sediments.
In acidic mining-impacted lake sediments, the microbial reduction of Fe(III) is the dominant electron-accepting process, whereas the reduction of sulfate seems to be restricted to a narrow sediment zone of elevated pH and lower amounts of total and reactive iron. To evaluate the microbial heterogeneity and the commensal interactions of the microbial community, the flow of supplemental carbon and reductant was evaluated in four different zones of the sediment in anoxic microcosms at the in situ temperature of 12 degrees C. Substrate consumption, product formation, and the potential to reduce Fe(III) and sulfate were similar with both upper and lower sediment zones. In the upper acidic iron-rich sediment zone, the rate of Fe(II) formation 204 nmol ml(-1) d(-1) was enhanced to 833 nmol ml(-1) d(-1) and 462 nmol ml(-1) d(-1) by supplemental glucose and H(2), respectively. Supplemental lactate and acetate were not consumed under acidic conditions and decreased the rate of Fe(II) formation to 130 nmol ml(-1) d(-1) and 52 nmol ml(-1) d(-1), respectively. When the pH of the upper sediment increased above pH 5, acetate-dependent reduction of sulfate was initiated even though the pool of Fe(III) was not depleted. In deeper sediment zones with elevated pH, the rapid consumption of acetate was always coincident to a decrease in the concentration of sulfate and soluble Fe(II), indicating the formation of Fe(II) sulfides. Although the reduction of Fe(III) was still an ongoing process in deeper sediment zones, the formation of Fe(II) was only slightly enhanced by the consumption of glucose or cellobiose, but not by H(2) or acetate. H(2)-utilizing acetogens seemed to be involved in the consumption of H(2). These collective results indicated (i) that the reduction of Fe(III) predominated over the reduction of sulfate as long as the sediment remained acidic and carbon-limited, and (ii) that the sulfate-reducing microbiota in this heterogeneous sediment were better adapted to the geochemical gradients present than were other neutrophilic dissimilatory Fe(III) reducers.
Küsel
K
Department of Ecological Microbiology, BITOEK, University of Bayreuth, 95440 Bayreuth, Germany
Dorsch
T