COMPARATIVE SCANNING ELECTRON MICROSCOPY STUDY OF ACID MINE DRAINAGE SEDIMENTS IN BIG MINE RUN NEAR ASHLAND, PENNSYLVANIA

A series of surface sediment samples were collected from Big Mine Run, a stream near Ashland, PA, severely impacted by acid mine drainage. Samples were taken both above and below the confluence between the acid stream and the outflow of treated water from an active coal mine. After oven drying, samples were coated with either gold or carbon and imaged using scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). Sediments from the acid stream site upstream of the confluence with the treated mine drainage were orange and dominated by aggregates of small (~2 µm diameter) spherical grains largely composed of iron and oxygen. Sediment grains from the treated water were dominated by aluminum and silica-rich angular particles that were much smaller than the iron-rich spheres. Downstream of the confluence with the treated water, iron-rich spheres were again found, attached to other grains and much less abundant than in the acid stream. The myxobacterium Gallionella has been documented to precipitate iron-rich spheres resembling the sediments we collected from Big Mine Run. It is likely that these sediments were also biologically precipitated by that same microorganism.