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At a 50-year-old coal mine drainage barrens in central Pennsylvania, USA, we evaluated the biogeochemistry of acidic, Fe(III)oxy(hydr)oxide precipitates in reclaimed plots and compared them to untreated precipitates in control areas. Reclaimed plots supported successional vegetation that became established after a one-time compost and lime treatment in 2006, while control plots supported biological crusts. Precipitates were sampled from moist yet unsaturated surface layers in an area with lateral subsurface flow of mine drainage above a fragipan. Fe(II) concentrations were three- to five-fold higher in reclaimed than control precipitates. Organically bound Fe and amorphous iron oxides, as fractions of total Fe, were also higher in reclaimed than control precipitates. Estimates of Fe-reducing and Fe-oxidizing bacteria were four- to tenfold higher in root-adherent than both types of control precipitates. By scaling up measurements from experimental plots, total Fe losses during the 5-yr following reclamation were estimated at 45 t Fe ha−1 yr−1. [Copyright &y& Elsevier]

Acid mine drainage ( AMD) barrens result from destruction of vegetation within AMD flow paths. When exposed to air, soluble iron in AMD undergoes oxidation and hydrolysis to form ferric iron (oxyhydr)oxides which accumulate on soil surfaces. A restoration experiment was conducted at a 50-year-old AMD barrens created by discharge from an abandoned underground coal mine. The objective was to determine whether vegetation could be established by altering rather than removing surface layers of acidic precipitates at a site representative of other mining-degraded areas. Three zones in the barrens were identified based on moisture content, pH (2.7-3.3), and thickness of precipitates (0-35 cm). Our hypothesis was that application of the same reclamation method to all zones would fail to sustain >70% vegetative cover in each zone after four growing seasons. The method consisted of applying 11 t/ha lime and 27 or 54 t/ha compost before rototilling (top 15 cm) and mulching with oat straw containing viable seeds for a nurse crop. Lime-only plots were included for comparison, and all amended plots were sown with a mine reclamation seed mix. Oats, sown species, and indigenous species dominated cover in the first, second, and fourth growing seasons, respectively. In the fourth year following reclamation, compost-amended plots had >70% cover and improved soil properties in all three zones, providing evidence to reject our hypothesis. Vegetative restoration of AMD barrens did not require removal of highly acidic precipitates, since they could be transformed at low-cost into a medium that supports indigenous plants. [ABSTRACT FROM AUTHOR]

The limited database of acidophilic or acidotolerant electrochemically active microorganisms prevents advancements on microbial fuel cells (MFCs) operated under low pH. In this study, three MFCs were used to enrich cathodic biofilms using acid mine drainage (AMD) sediments as inoculum. Linear sweep voltammetry showed cathodic current plateaus of 5.5 (± 0.7) mA at about − 170 mV vs Ag/AgCl and 8.5 (± 0.9) mA between − 500 mV to − 450 mV vs Ag/AgCl for biofilms developed on small graphite fiber brushes. After gamma irradiation, biocathodes exhibited a decrease in current density approaching that of abiotic controls. Electrochemical impedance spectroscopy showed six-fold lower charge transfer resistance with viable biofilm. Pyrosequencing data showed that Proteobacteria and Firmicutes dominated the biofilms. Acidithiobacillus representatives were enriched in some biocathodes, supporting the potential importance of these known iron and sulfur oxidizers as cathodic biocatalysts. Other acidophilic chemolithoautotrophs identified included Sulfobacillus and Leptospirillum species. The presence of chemoautotrophs was consistent with functional capabilities predicted by PICRUSt related to carbon fixation pathways in prokaryotic microorganisms. Acidophilic or acidotolerant heterotrophs were also abundant; however, their contribution to cathodic performance is unknown. This study directs subsequent research efforts to particular groups of AMD-associated bacteria that are electrochemically active on cathodes. [ABSTRACT FROM AUTHOR]

Low-pH and low-nutrient conditions make the establishment of vegetation in mining-impacted environments particularly challenging. This study was conducted on soils forming from secondary Fe mineral precipitates in experimental plots at a 50-year-old acid mine drainage (AMD) barrens in Central Pennsylvania, U.S.A. Our objective was a qualitative assessment of bacterial and eukaryal diversity in reclaimed precipitates supporting dense successional vegetation six years after a single addition of lime (to raise pH from 2.5 to 4.5) and a single incorporation of compost. At the time of sampling, the pH of reclaimed precipitates had declined to initial values (2.5–2.7) and was similar to that of control precipitates supporting indigenous biological crusts. Microbial diversity was compared using 454 pyrosequencing of 16S rRNA genes (V1-V5) and 18S rRNA (V4-V5) in upper layers (adhering to roots and crusts) and lower layers (below roots and crusts). A total of 1721 bacterial OTUs at 97% similarity and 307 eukaryal OTUs at 97% similarity were recognized in the entire dataset. Despite similar pH, reclaimed precipitates had more diversity than control precipitates. Proteobacteria and Actinobacteria were the most abundant bacterial phyla in reclaimed and control precipitates, respectively. Acidobacteri a were more abundant in root-and crust-enriched layers than in the underlying precipitates containing less carbon. Basidiomycota fungi were the most abundant classified eukaryotes in reclaimed precipitates, while Bryophyta dominated control precipitates. Glomeromycota were observed in reclaimed but not in control precipitates, where Ascomycota were the most abundant fungi. After the one–time reclamation approach, bacterial richness in AMD precipitates was three-fold lower than that determined for acid sulfate soils using closed reference OTU picking. These results suggested the need for further lime and compost incorporation to increase soil functionality. [ABSTRACT FROM AUTHOR]

Abstract: Peatlands effectively retain heavy metals and prevent stream and watershed contamination. Sulfate reduction is considered the most significant process of metal immobilization in natural wetlands and microbial sulfate reduction is the presumed mechanism that results in the precipitation of metal sulfides. In this study, we examined the biogeochemical mechanisms involved in zinc retention and accumulation in a metalliferous peatland of western New York. In the reducing conditions of these peatlands zinc sulfides occurred as framboidal aggregates of sphalerite and polytypic wurtzite (2nH, n ⩾2) nanocrystallites associated with bacterial cells and organic matter. Bacterial cells were co-located with ZnS inside peat particles where the microenvironment remained anoxic. The peat zinc sulfide was depleted in 34S isotopes relative to the sulfate supplied to the peatland by 18–34 per mill, implicating its biological formation. Extraction of microbial community DNA from peat samples yielded diverse PCR amplicons from dissimilatory sulfite reductase (dsrAB) genes, indicating varied bacterial taxa capable of reducing forms of oxidized sulfur. Nanocrystals with distinct structural features were observed in samples containing contrasting dsrAB sequences. The results of this investigation provide clear evidence that microorganisms can influence the chemical forms of heavy metals in peatland environments. Our findings also provide insight into the conditions necessary to promote the immobilization of chalcophile elements in engineered systems for the treatment of acid mine drainage and wastewater effluents. [Copyright &y& Elsevier]