It’s not hard for everyday citizens to take a position on mountaintop coal mining. The web is scattered with nasty before-and-after photos of mine sites and gripping narratives of environmental degradation. But sometimes it can be tough to hear the science over the screaming. After all, few of us spend time digging through scientific literature or navigating EPA’s website.

In 2011, EPA released a report (actually, a literature review) summarizing the effects of mountaintop mining and valley-fill (MTM-VF, aka mountaintop removal) on stream ecosystems. They concluded that mountaintop removal affects streams in 5 ways, which I briefly summarize below.

1. Headwater streams are entirely removed. Removing mountaintops to expose internal coal seams generates excess waste. This “overburden” is typically disposed of in valleys near mine sites…and at the bottom of those valleys lie headwater streams. Valley fill doesn’t just degrade streams—it removes them from the landscape. In fact, EPA estimated that valley fill removed 1208 miles of headwater streams between 1992 and 2002.

2. Water quality changes dramatically. Mountaintop removal typically results tenfold increases in dissolved ions such as sulfate, bicarbonate, calcium, potassium, sodium and chloride. These increased are cumulatively evident in increased specific conductance (conductivity) and total dissolved solids. Other studies have found decreased temperature variability and increased in fine sediments.

3. Water is often acutely toxic to organisms. Toxicity tests measure survival of crustaceans (Cerodaphnia dubia) or fish (fathead minnow Pimephales promelas) in undiluted test water over 48- to 96-hour periods. Several studies using water or sediments collected downstream from valley fill sites showed significant toxicity. Because valley fill effluent has elevated concentrations of multiple ions which interact with one another under different conditions, assigning toxicity effects to one specific pollutant is difficult.

4. Harmful levels of selenium causes deformities and death. In headwater streams, dissolved selenium is typically taken up by periphyton growing on rocks and fallen trees. Selenium is a classic bioaccumulator—so the higher up on the food chain an organism is, the more likely it is to be affected by selenium. Selenium is most notorious for causing skeletal deformities in fish, which typically leads to early mortality. High selenium concentrations in aquatic-feeding birds can also greatly reduce hatching success.

5. Biotic communities are degraded. Effects of MTR probably are most evident in biotic community structure. Scientists often use indices of biotic integrity (IBIs) to make sense of complex community patterns. Most studies of stream biota downstream of MTR sites have shown decreased fish and invertebrate IBI scores. The reduced invertebrate IBI scores typically come from decreased proportions of sensitive taxa, particularly mayflies. For example, invertebrate communities in unmined headwater streams typically have about 50% mayflies, while streams near mines have around 1%. Similarly, reduced fish IBI scores were attributable to few minnow species, which may be more sensitive to high ion concentrations, and to fewer benthic insectiveores, whose food sources is affected by sedimentation from MTR mines.

—Brandon Peoples