From stream to sky: AMD’s biological reach
by Andy McAllister, Watershed Outreach Coordinator
In many abandoned mine drainage (AMD) discharges, metal contamination is evident from copious amounts of metals precipitating on the streambed. But other discharges are crystal clear, appearing uncontaminated to the unknowing public. This clear water is often much more deadly to aquatic organisms. Acidity and aluminum are two likely components of clear AMD that can have far-reaching effects on stream biology.
Even without dissolved metals, AMD’s low pH has significant sublethal effects on aquatic macroinvertebrates and, to a lesser degree, fish. Sublethal effects include behavioral changes in activity and mobility. While not always directly deadly to invertebrates, it appears that acidic AMD affects the ability of the macroinvertebrates to feed and move around in the stream, which ultimately has a longterm effect on the invertebrate populations and the animals that prey on them.
As one of the most common elements on Earth, aluminum generally does not interfere with the daily lives of aquatic organisms. However, in high concentrations dissolved in AMD, aluminum has a devastating impact. Besides harming fish and aquatic macroinvertebrates, aluminum has further implications for the terrestrial environment: reduced hatching success and other toxic effects have been reported in birds that feed on freshwater invertebrates that have bioaccumulated aluminum. Aluminum and manganese are also known to impair growth in plants around acidic mine spoils.
Read more about the effects of acid and aluminum on both revegitation and aquatic life from the following chapters of PA DEP’s Coal Mine Drainage Prediction and Pollution Prevention in Pennsylvania:
- Impacts of Mine Drainage on Aquatic Life, Water Uses, and Man-Made Structures by Jane Earle and Thomas Callaghan
- Reclamation and Revegetation by Nevin Strock
October 9th, 2006 at 5:49 pm
I’d like to point out that sulfate reducing bioreactors, which are know to precipitate metal sulfides such as FeS (acid-volatile sulfide, not pyrite) also are known to precipitate aluminum hydroxy-sulfates (B.T. Thomas, 2002). These aluminum mineral phases do not tend to plug the reactors like pure limestone systems which plug with aluminum hydroxide/gibbsite.
Bench and pilot testing of the SRBR technology at the Fran Mine in Clinton County, PA did a fine job of removing aluminum at concentrations up to about 240 mg/L. I believe the Yellow Creek Phase 2B SRBR in Indiana County has been handling aluminum at concentrations of about 40 mg/L since it was built in late 2003.