Potential for passive mitigation of coal-derived acid mine drainage in abandoned stream channels

Passive treatment of coal mining-derived acid mine drainage (AMD) utilizes natural processes to neutralize the acidity and remove dissolved metal contaminants. In some cases, microbial communities develop, with no human intervention, that can induce the removal of harmful components of AMD (e.g. acidity, dissolved Fe, Al, and Mn). To better understand how these beneficial processes might develop, we studied the Huff Run system in eastern Ohio, where a portion of the stream was artificially diverted to prevent direct entry of AMD into the stream. There are now two abandoned channels of the stream that now receive raw AMD, and we hypothesized that the increased residence time of the AMD in these abandoned channels could result in diminished AMD impact on Huff Run. We tracked seasonal changes in the aqueous chemistry and microbiology through two abandoned channels, referred to as Farr and Lyons. The Fe, Al, and Mn were removed from solution as AMD moved through the Farr channel, with net alkaline water, and abundant Bacillus and Paenibacillus phylotypes. Dissolved Fe was removed from AMD over the course of the Lyons channel, but neither Al nor Mn were, and the sediments contained abundant phylotypes attributable to Alicyclobacillus sp., which are capable of oxidative precipitation of Fe(II) under acidic conditions. Our results indicate that the enhanced AMD retention in the abandoned channels can lead to removal of metals from AMD. This appears to occur due to abiotic and microbiological processes, which are controlled by AMD chemistry.