Surface mining for coal – which can include including strip mining, open-pit mining and mountaintop removal mining – has been widely scrutinized for its potential impacts on water quality, animal development and the health of plants along rivers and streams. Duke University’s Emily Bernhardt and her colleagues have recently published several high-profile papers that are providing cutting-edge science to help inform the debate about mountaintop mining for coal. EarthSky blogger Benjamin D. Duval had the opportunity to speak with Dr. Bernhardt to understand how mining impacts river ecosystems, the policy implications of this research, and about what can be done to restore Appalachian landscapes degraded by coal mining.
Surface mining for coal has altered the landscape of the Appalachian region. Please describe this mining method. Why are environmentalists concerned about it?
Sure. Surface coal mining allows mining companies to access shallow seams of coal that they can’t get to with traditional underground mining. These coal seams are usually within 700 feet of the soil surface, and mining companies access them by dynamiting off the overlying soil and rock.
The coal seams can be quite thin but getting to them generates an enormous volume of waste rock. The problem is that this waste rock needs to be moved out of the way to allow continued mining, and the obvious place to put this waste, or overburden, is in adjacent stream valleys. The practice has come to be known as mountaintop mining with valley fills – because it involves blowing the tops off of mountains and disposing of them in valleys.
Currently, more than 5% of the land surface area of the Central Appalachians has been converted from forests into active and reclaimed surface mines, making it the dominant form of land use change in the region.
This represents a substantial loss of Appalachian forest habitat, because mining companies have been largely unsuccessful in establishing trees on reclaimed mines. It also means that now buried streams are flowing through mining overburden and delivering large quantities of rock and coal derived salts to Appalachian rivers. Streams and rivers downstream of mines become increasingly saline and this leads to the local extinction of many freshwater organisms that can’t handle the salts.
Mining overburden also generates several potentially toxic trace elements that are damaging downstream wildlife. Selenium is of particular concern because it is a prevalent trace element in coal and in shale rock that is easily leached into surface and ground water. Selenium bio-accumulates in algae and stream insects and can leads to significant mortality and growth deformities in the fish and birds that eat them. I have spent a great deal of time over the last several years trying to understand how the hundreds of individual mines within Appalachia are collectively degrading the water quality of the region.
Your July 2012 paper in the journal Environmental Science and Technology reports strong correlations between mining residues like sulfate and increases in electrical conductivity, and mining activity levels. Why are these variables specifically harmful to stream health?
Electrical conductivity is the quick and dirty way that we can measure the salinity of a freshwater. Water containing more dissolved salts, or ions, more readily conducts electricity.
We know that salinity is stressful for freshwater organisms whose physiology is adapted to maintaining saltier internal conditions than the surrounding water. By simply making it harder for aquatic organisms to maintain osmotic balance, the increase in salinity can be stressful.
Sulfate is a dominant ion in surface coal mining waste – and much of it is generated directly from coal minerals. Sulfate was basically laid down by bacteria as pyrite (FeS2) minerals back in the Carboniferous period, 300-350 million years ago, when this coal was first created as the sediments of large tropical swamps.
As long as the coal is isolated from oxygen in the atmosphere, the sulfur stays bound in the mineral. Once coal is brought to the surface, the pyrite rapidly oxidizes to dissolved iron oxides, sulfate and hydrogen ions. High sulfate concentrations are probably not themselves responsible for the loss of aquatic biota, but elevated sulfate concentrations in stream water is a sure sign that a stream is receiving significant amounts of mining derived effluent.
Since coal contains all sorts of trace elements (selenium, manganese, arsenic, aluminum) we can expect many of these ions to also be elevated. Sulfur becomes problematic to many organisms once it gets into the sediments where microbes in the absence of oxygen can convert the sulfate to sulfide, a very potent toxin to many microbes and plants.
Previous work by your group also suggests direct harm to several fish species by mining waste. Does your new work also imply indirect effects due to disruptions in stream food webs?
That’s a great question and one that we are currently pursuing in our research. The loss of nearly all of the insect herbivores, leaf shredders and predators from mined streams has to have important effects on the way energy and nutrients are moving through stream food webs. Many sensitive native fish are absent in mined streams, but a number of tolerant fish remain even immediately below valley fills. We wonder what the fish are eating now that the mayflies and stoneflies are gone? How are their altered diets affecting the potential for biomagnification of selenium?”
You and your colleagues’ research on mountain top surface mining has obvious implications for environmental policy. Have your findings been implemented into any recent laws? Are there any major court decisions expected on the horizon for regulating surface mining based on watershed quality?
I have never had research that was so immediately relevant and useful to policymakers. Our findings have been part of testimony in several lawsuits and in a hearing before West Virginia’s water quality board.
In all cases, the judge or the panel of experts has been thoroughly convinced by the science – with decisions concluding that there is clear and irrefutable evidence of cumulative impacts of surface mining on regional water quality. The resulting decisions however, are often based on legal precedent rather than scientific evidence.
The rapidly growing body of work on the extensive environmental and human health consequences of this mining practice is making it more and more difficult for mining companies to claim that a new mine permit will have no impact.
This is a small but important step towards injecting better science into the regulation of new mining activity.
What are the next questions that need to be answered related to mountain top surface mining, and how is your group addressing those questions?
One of the major questions we are pursuing now is to examine the variation in pollution export across surface coal mines. We are expanding our fieldwork to collect drainage waters from mines in all stages of development – abandoned, reclaimed, in reclamation and active – and under varying fill management approaches. We want to understand how fill age, fill volume and fill construction affect the extent of mining pollutants produced.
Ideally, we would love to find some outliers, where surface mines are not generating significant pollutant loads, because those outliers could provide important information that could help us reduce future mining pollution.
We have preliminary evidence suggesting that some of the oldest mountaintop mines in Appalachia, which were judged fully reclaimed more than 15 years ago, are still releasing stream water with the salinity and ionic composition of currently active mines.
Regardless of the political and regulatory decisions about future mining, it’s clear that major efforts need to be made to clean up the mining pollution that has already been generated throughout the region.
Bottom line: EarthSky blogger Benjamin D. Duval spoke with Dr. Bernhardt to understand how mining impacts river ecosystems, the policy implications of this research, and about what can be done to restore Appalachian landscapes degraded by coal mining.