『Abstract
　Ground water systems dominated by iron- or sulfate-reducing conditions may be distinguished by observing concentrations of dissolved iron (Fe²⁺) and sulfide (sum of H2S, HS^-, and S^2- species and denoted here as “H2S”). This approach is based on the observation that concentrations of Fe²⁺ and H2S in ground water systems tend to be inversely related according to a hyperbolic function. That is, when Fe²⁺ concentrations are high, H2S concentrations tend to be low and vice versa. This relation partly reflects the rapid reaction kinetics of Fe²⁺ with H2S to produce relatively insoluble ferrous sulfides (FeS). This relation also reflects competition for organic substrates between the iron- and the sulfate-reducing microorganisms that catalyze the production of Fe²⁺ and H2S. These solubility and microbial constraints operate in tandem, resulting in the observed hyperbolic relation between Fe²⁺ and H2S concentrations. Concentrations of redox indicators, including dissolved hydrogen (H2) measured in a shallow aquifer in Hanahan, South Carolina, suggest that if the Fe²⁺/H2S mass ratio (units of mg/L) exceeded 10, the screened interval being tapped was consistently iron reducing (H2 〜0.2 to 0.8 nM). Conversely, if the Fe²⁺/H2S ratio was less than 0.30, consistent sulfate-reducing (H2 〜1 to 5 nM) conditions were observed over time. Concomitantly high Fe²⁺ and H2S concentrations were associated with H2 concentrations that varied between 0.2 and 5.0 nM over time, suggesting mixing of water from adjacent iron- and sulfate-reducing zones or concomitant iron and sulfate reduction under nonelectron donor-limited conditions. These observations suggest that Fe²⁺/H2S mass ratios may provide useful information concerning the occurrence and distribution of iron and sulfate reduction in ground water systems.』

Introduction
Methods
Hyperbolic relation between Fe²⁺ and H2S concentrations
Distinguishing iron from sulfate reduction
Conclusions
Acknowledgments
References