State Water Resources Research Institute Program

Project ID: 2007PA74B
Title: The effect of oxygen availability on Fe cycling microbial communities within an acid mine drainage-induced-kill zone
Project Type: Research
Start Date: 3/01/2007
End Date: 2/29/2008
Congressional District: 9th
Focus Categories: Ecology, Geochemical Processes, Surface Water
Keywords: acid mine drainage, iron-oxidizing bacteria, iron-reducing bacteria
Principal Investigators: Senko, John M.; Bruns, Mary Ann; Burgos, William
Federal Funds: $ 19,668
Non-Federal Matching Funds: $ 39,336
Abstract: Acid mine drainage (AMD) that emanates from abandoned and active coal mines represents Pennsylvania's largest surface water pollution problem. The most prominent feature of AMD-impacted streams is the appearance of an orange Fe(III) (hydr)oxide precipitate (known as "yellowboy") which arises when low pH, Fe(II)-rich AMD enters oxic streams, where the pH increases allowing for rapid oxidation of Fe(II) and subsequent hydrolysis of Fe3+. The resulting yellowboy coats stream beds and ultimately kills most large aquatic life. Many passive treatment approaches for the neutralization of and removal of Fe from AMD require the use of limestone that neutralizes the acidity of AMD and allows for rapid oxidation and precipitation of Fe. The neutralized and Fe-free water can then be safely released to streams. However, the Fe(III) (hydr)oxides that are formed coat limestone and limit its reactivity. An attractive alternative to this approach is to remove Fe from AMD at low pH followed by neutralization of Fe-free water with limestone. This would significantly lengthen the lifetime of limestone in AMD treatment systems. We have identified an AMD-induced kill zone (designated Gum Boot) in McKean County, PA where Fe is completely removed from AMD as it flows along a 15 m path from its emergence point. We have shown that this Fe removal can be attributed to the microbiologically-mediated oxidation of Fe(II) and subsequent hydrolysis and precipitation of Fe(III). Our goal is to characterize bacterial communities associated with Gum Boot kill zone sediments and identify Fe(II) oxidizing bacteria by manipulating the availability of oxygen in Gum Boot kill zone sediment-containing microcosms. The response of the microbial community to different dissolved oxygen regimes will be assessed by culture-dependent enumerations of Fe(II) oxidizing and Fe(III) reducing bacteria as well as through nucleic acid-based microbial community analysis. This approach will allow us to characterize the microbial communities associated with the kill zone sediments, identify Fe(II) oxidizing bacteria and predict their physiological requirements. Based on the requirements of the predominant Fe(II) oxidizing bacteria, we will be better able to stimulate Fe(II) oxidizing bacterial activity to remove Fe from AMD in other kill zones or design kill zones for the low-pH removal of Fe form AMD.

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