ISSN:
1745-6584
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Energy, Environment Protection, Nuclear Power Engineering
,
Geosciences
Notes:
The Middendorf aquifer of South Carolina exhibits a 40-kilometer-wide zone where dissolved ferrous iron concentrations commonly exceed 1 mg/I. Downgradient of this zone, dissolved iron concentrations decrease to less than 0.05 mg/1. Geochemical and microbiologie evidence indicates that this zonation reflects the competitive exclusion of sulfate-reducing activity by Fe(IH)-reducing bacteria in the high-iron zone and the emergence of sulfate reduction as the predominant process in the low-iron zone. Viable Fe(III)- and sulfate-reducing bacteria coexist throughout the aquifer. However, the observed linear relationship between dissolved iron and dissolved inorganic carbon as well as the lack of sulfate consumption indicates that sulfate-reducing bacteria are much less active than Fe(III)-reducing bacteria in the high-iron zone. Fe(III)-reducing bacteria appear to exclude sulfate-reducing activity by maintaining dissolved hydrogen (˜1.0 nM), formate (˜2.0 μM), and acetate (˜1.0 μM) concentrations at levels lower than thresholds required by sulfate-reducing bacteria. Downgradient of the high-iron zone, Fe(III)-reducing activity becomes limited by a lack of Fe(III) oxyhydroxides as Middendorf sediments become progressively more marine in origin. Hydrogen, formate, and acetate concentrations then increase to levels (˜3.0 nM, ˜10.9, and 2.5 μM, respectively) that allow sulfate-reducing bacteria to become active. Increased sulfide production strips ferrous iron from solution by precipitating ferrous sulfides, and dissolved iron concentrations decrease. The observed high-iron zonation is thus one manifestation of microbial competition for scarce substrates. The wide occurrence of similar water-chemistry patterns implies that microbial competition mechanisms are important to the ground-water geochemistry of many hydrologie systems.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1745-6584.1992.tb00808.x
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