Bioremediation and biogeochemistry in acid mine drainage.
Acid mine drainage (AMD) is an environmental problem affecting watersheds across the globe. AMD forms when mining exposes pyrite containing rocks and the pyrite is oxidized. This results in the release of acidic and metal laden water - not a friendly environment for fish and aquatic insects. Acid-loving (acidophilic), iron-oxidizing bacteria thrive in these environments.
Iron-oxidizing bacteria generate their energy by transforming iron from its soluble form Fe(II) to its insoluble form Fe(III). The insoluble Fe(III) reacts with oxygen in the water to form rust-like iron oxide minerals (e.g. schwertmannite). These microbes can be put to work to help remediate AMD environments. |
My collaborators at Penn State and I began to study AMD environments in Pennsylvania by studying the geochemistry and microbial communities in AMD sites across the state. This work lead to a better understanding of the environmental parameters that control where species live and is detailed in these 2013 and 2014 papers. Collaborators from the University of Cincinnati (now University of Minnesota) and I did similar work in KY and you can see the results in this 2016 paper. |
My collaborators then did a survey of iron-oxidation rates across AMD sites in PA and the Iberian Pyrite Belt, Spain. You can see their results here. Based on these results, we focused our efforts on Scalp Level Run, the site that had the highest rate of iron oxidation. Fast iron-oxidation rate = Fast removal of the system = A good thing for remediation We found that the microbial community at Scalp Level Run was dominated by Ferrovum species, not diverse, and did not change across the length of the outflow. You can see these results in this 2017 paper and a news story about our work. |
Bioremediation is about more than just identifying the microbial communities responsible for iron-oxidation. It is about finding a way to maximize their activities. Toward this end, we performed experiments wherein we systematically varied the concentration of iron and the pH in chemostats to determine how community composition and iron-oxidation rates change with these variables. We found that iron-oxidation is fastest at low pH and in low diversity communities. You can read about these results in our 2016 and 2017 papers. |
Through time, it became apparent that it isn't only what's on the surface that counts. At some AMD sites, like Scalp Level Run, the AMD effluent runs almost exclusively above ground. At other sites, like Brubaker Run, a large portion of the water follows underground (see my collaborators' paper about this here). So, we began investigating subsurface communities and geochemistry at Brubaker Run. We installed subsurface "peepers" to examine geochemistry and took cores to look at microbial community composition and mineralogy. We found that the geochemistry, microbial communities and mineralogy are significantly different in the subsurface than in the surface. This may have profound effects on bioremediation in these systems. We look forward to submitting this work in the near future, so stay tuned!
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Collaborators at UC Davis and the USGS and I also began to study subsurface microbial communities in a reservoir constructed to contain AMD from the Iron Mountain Mine, CA. Here, we found that surface and subsurface microbial communities. We just submitted a proposal to the NSF Geobiology and Low-Temperature Geochemistry program to continue our work in this exciting system.
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Curious how I got in to AMD research? It all began as part of a field course I took as a graduate student at Penn State. We examined the geochemistry and microbial communities in Peña de Hierro, an acidic pit lake in the Rio Tinto region, Spain. We got to learn basic geochemical analyses, sample collection, microscopy, and DNA based analysis. That student lead work is now in review at Frontiers in Microbiology. I am very grateful that I got such amazing field work experience as a student and am dedicated to providing similar opportunities to my future students. |