Acid mine drainage (AMD), is formed due to exposure of the mineral pyrite to air and water which in turn leads to the formation of H2SO4 and iron hydroxide. Elevated acidity along with high concentrations of iron, sulfate, and soluble toxic metals are characteristics of AMD which adversely affect aquatic life. Thus AMD is a significant environmental hazard that affects aquatic ecosystems around the world. Although extreme environments like AMD affected sites have negative impacts on macrofauna, these seemingly inhospitable conditions provide suitable environments for acidophilic microbial communities. AMD environments harbor naturally occurring microbial communities that have opportunities for mutualistic relationships as they co-exist in mixed species communities. In fact, microbial communities that inhabit AMD sites further deteriorate conditions by contributing to the maintenance of acidity. Various restoration projects are adopting management strategies to control AMD; use of limestone is one approach for mitigation of the effects of acid pollution. In this study, we elucidate the direct and indirect effects of chemical remediation on AMD impacted microbial communities.
Results/Conclusions
To meet our objectives, water and sediment samples were collected on four dates from three sites along an AMD impacted stream (a tributary of Huff Run, Mineral City, OH, USA) that was targeted for remediation. Two control sites (positive, which was not being remediated, and negative, which was not AMD impacted) were also located in this watershed. The pH of the study stream ranged from 2.5-5.5 prior to remediation and increased downstream. pH remained almost uniform, at 3.5, along the stream during remediation and increased about two fold after remediation (6.7-7.1). Turbidity was low (0.42 to 0.50 NTU) before remediation and increased uniformly during remediation (18.0-20.2 NTU) but declined after remediation (6.0-12.0 NTU). A steady decrease in conductivity was observed during remediation. Examination of the microbial communities were carried out by fluorescent microscopy (DAPI staining), DNA extraction followed by amplification of a fragment of 16S rRNA gene and analysis via denaturing gradient gel electrophoresis (DGGE). About a 9-10 fold increase in bacterial numbers was observed following remediation and the DGGE results revealed differences in community structure, pre- and post-remediation. Our results demonstrate alterations in AMD associated microbial communities caused by remediation as a result of dramatic environmental change.
