| Acid mine drainage (AMD) barrens result from the death of vegetation resulting from overland flow of acidic metal-rich waters emerging from abandoned underground mines. In 2006, a restoration experiment was conducted by our research group at a 50-year-old AMD barrens to determine whether vegetation could be established by altering, rather than removing, surface layers of acidic iron-rich precipitates at the site which is representative of other mining-degraded areas. This dissertation builds on the investigation initiated in 2006 in the zone where subsurface AMD flow was most shallow and focuses on non-reclaimed (control) precipitates covered by mossy biological crusts and reclaimed precipitates sustaining vegetation.;Iron (Fe) biogeochemistry in AMD precipitates was studied to gain an understanding of potential losses of redox-active metals after plant-based reclamation. As mobility of redox-active metals can be increased by enhanced microbial activity in the rooting zones of growing plants, we compared the forms of Fe in the reclaimed and control precipitates five years post-reclamation. Since Fe is the most abundant metal in many mine drainages, root exudation by growing plants could stimulate Fe(III)-reducing activity in rhizospheres, resulting in losses of soluble Fe(II) from the system. Precipitates were sampled from moist yet unsaturated surface sections (8-cm depth) excised from replicate plots. Ferrozine tests of extracts indicated that Fe(II) concentrations were three- to five-fold higher in reclaimed precipitates than in control precipitates.;Microbial communities inhabiting AMD-impacted environments have been more extensively studied in aqueous rather than terrestrial systems. Our reclamation study provided the opportunity to gain insights into AMD-derived bacterial and eukaryotic communities in unsaturated, edaphic habitats. Precipitates of the same types as described for the Fe-biochemistry study (RR, RB, CC, and CB) were collected six years post-reclamation. At the time of sampling, all four precipitate types had similar pH levels (2.5-2.7) because reclaimed precipitates had gradually become more acidic following the one-time lime application in 2006. Bacterial and eukaryotic diversity were assessed using 454 pyrosequencing of 16S rRNA (V1-V3/V5 region) and the 18S rRNA (V4-V5 region) genes. Contrary to our projections we observed high bacterial and eukaryotic diversity across all samples.;For bacterial libraries, we recovered a total of 3,150 operational taxonomic units (OTUs) at 97% similarity. Approximately 50% of these were exclusively found in reclaimed precipitates (RR, RB or both), 33% were unique to control precipitates (CC, CB, or both), and 6% were shared among the four precipitate types. Nineteen phyla were identified in the four type of precipitates and 13 of these were found in all samples. Proteobacteria comprised the most abundant representatives in reclaimed precipitates while Acidobacteria were more abundant in root-and crust-adherent precipitates.;Eukaryotic diversity was also higher in reclaimed precipitates than in control precipitates, reflecting the positive influence of plant establishment. Of the total 494 OTUs identified at the 95% similarity level, about 62% were found exclusively in reclaimed precipitates (RR, RB or both), 20% were unique to control precipitates (CC, CB, or both), and only 7% were shared among the four precipitate types. Since libraries from control precipitates were dominated by bryophyte sequences, these and other macroeukaryotic sequences were removed before calculating the percentages of microeukaryotic taxa in each precipitate. The main microeukaryotic taxa identified in reclaimed precipitates were Basidiomycota, 48% in RR and 39% in RB. In contrast, Ascomycota were more abundant in control precipitates, 50% in CC and 18% in CB, reflecting a shift in fungal community composition following reclamation. Many taxa reported to be abundant in water-impacted AMD habitats were either very low in abundance or not detected. (Abstract shortened by UMI.). |
