Abandoned Mine Posts

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.

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by Andy McAllister, Watershed Outreach Coordinator

Sampling an abandoned mine drainage (AMD) discharge during the “dog days” of summer can be a refreshing experience, because AMD temperatures remain fairly constant, often in the upper 50°s F. Groundwater in the upper 300 feet or so is normally a couple of degrees warmer than the average yearly air temperature; in Pittsburgh, that average yearly air temperature is 53° F. In the hottest summer months, this cool water can be quite a relief for coldwater fish and overheated biologist alike.

Fish such as trout can be found in some AMD-polluted streams near the confluence with another stream. They use the cool water as a thermal refuge, swimming in and out to escape the warmer water in larger streams. Fish will consume macroinvertebrates living in the AMD-impacted stream, but more often than not, metal precipitate and pH levels prevent any sustainable macroinvertebrate populations to serve as prey, forcing the fish to venture back to the warmer stream to find food.

This cooler water may be just the ticket to help turn a liability into an asset: mine discharges continue to be examined for their potential in aquaculture and cooling buildings or power plants.

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