Application of a Depositional F acies Model to an Acid Mine Drainage Site

Abstract

Lower Red Eyes is an acid mine drainage site in Pennsylvania where low-pH Fe(II) oxidation has created a large, terraced iron mound downstream of an anoxic, acidic, metal-rich spring. Aqueous chemistry, mineral precipitates, microbial communities, and laboratory-based Fe(II) oxidation rates for this site were analyzed in the context of a depositional facies model. Depositional facies were defined as pools, terraces, or microterracettes based on cm-scale sediment morphology, irrespective of the distance downstream from the spring. The sediments were composed entirely of Fe precipitates and cemented organic matter. The Fe precipitates were identified as schwertmannite at all locations, regardless of facies. Microbial composition was studied with fluorescence in situ hybridization (FISH) and transitioned from a microaerophilic, Euglena-dominated community at the spring, to a Betaproteobacteria (primarily Ferrovum spp.)-dominated community at the upstream end of the iron mound, to a Gammaproteobacteria (primarily Acidithiobacillus)-dominated community at the downstream end of the iron mound. Microbial community structure was more strongly correlated with pH and geochemical conditions than depositional facies. Intact pieces of terrace and pool sediments from upstream and downstream locations were used in flowthrough laboratory reactors to measure the rate and extent of low-pH Fe(II) oxidation. No change in Fe(II) concentration was observed with 60 Co-irradiated sediments or with no-sediment controls, indicating that abiotic Fe(II) oxidation was negligible. Upstream sediments attained lower effluent Fe(II) concentrations compared to downstream sediments, regardless of depositional facies.

Geochemical Niches of Iron-Oxidizing Acidophiles in Acidic Coal Mine Drainage

“…S2 in the supplemental material) (7). Dissolved oxygen was below detection at the emergent springs and approached saturation at all downstream sites (7,12). In January 2011, thick ice prevented further downstream sampling at URE.…”

“…Our results do not exclude the possibility that pe, Fe 3ϩ , or other parameters may play a role in determining microbial distributions at other AMD sites. The Red Eyes springs have only minor variations in dissolved trace metal and phosphorus concentrations (7,12), a characteristic which may have allowed us to isolate the effects of pH, pe, and Fe on microbial community composition. Globally, AMD discharges are complex environments that encompass a much wider range in temperature, pH, conductivity, metal concentrations, and other environmental parameters that are potentially important for defining microbial niches.…”

“…Microbial communities that develop naturally in AMD sediments also have different iron oxidation capabilities. In experiments with sediments from the Lower Red Eyes coal mine drainage in Pennsylvania, USA, cell-normalized iron oxidation rates were nearly twice as fast in reactors incubated with Ferrovum-dominated sediments as with Acidithiobacillus-dominated sediments (7). In a subsequent study, cell-normalized iron oxidation rates determined for AMD sediments from multiple drainages with different microbial assemblages varied by up to 7 times (12).…”

“…Previous work at Lower Red Eyes showed that sediment microbial communities change with distance across the mound and that distinct sediment communities exhibited different cell-normalized iron oxidation rates (7). In order to identify which variables controlled the distribution of acidophiles at Upper and Lower Red Eyes, we performed a detailed analysis of microbial communities in and downstream from the two discharges, including seasonal changes.…”

Oxygen-dependent niche formation of a pyrite-dependent acidophilic consortium built by archaea and bacteria

“…is meanwhile a third candidate for playing a role in ferrous iron oxidation at acidic conditions (Hallberg, 2010). Brown et al (2011) andJones et al (2011) proposed recently that pH and ferrous iron concentration could dictate whether Ferrovum or Acidithiobacillus might dominate a microbial consortium. Their assumption is corroborated by the results from this and a previous study from Ziegler et al (2009).…”