Every summer sections of the nearby Kiski (more properly called the “Kiskiminetas”) River turn the chartreuse green of Mountain Dew. This year the color transformation has occurred a month or so earlier than usual. The color reflects some interesting aspects of the ecology of both the river and its watershed.
The hillsides all along the Kiski River have been extensively mined for coal. There are deep mines that tunnel into the heart of the underlying rock and strip mines that have scraped away their surfaces. Both of these types of mines have disturbed the covering and encasing rocks of the coal seam, and these overburden rocks are rich in a mineral called pyrite. Pyrite is a gold-colored mineral that is commonly called “fool’s gold.” Pyrite is most properly iron sulfide (FeS2).
When pyrite is exposed to oxygen and water it vigorously oxidizes into an array of molecules of iron and sulfur. Ferrous iron oxides (Fe2O3 (“rusts”)) make the red smears in the waters running out of exposed pyrite-rich sites. Ferrous hydroxides (Fe (OH)3 (“yellow boy”) makes the orange silts that collect on the rocks over which the waters from an exposed pyrite layer are running. Much less visible that these iron compounds, though, but much more dangerous, is the sulfuric acid (H2SO4) that forms from sulfur oxidation. The sulfuric acid quickly overwhelms the natural buffering capacity of stream water’s dissolved bicarbonate and plunges the pH of the stream to toxic levels. This sulfuric acid generation and dispersal is called Acid Mine Drainage (AMD).
The picture to the left shows a hillside section along the Kiski River where uncontrolled acid mine drainage has erased the site’s vegetation and left a flowing, orange and red stream in its place. This particular site was too close to the Kiski River to be effectively cleaned up or sealed away from draining into the stream. It stands as an on-going reminder of the horror of AMD! To me, it looks like the surface of Mars!
The water from this pyrite-rich spot and probably from hundreds of other, less obvious locations throughout the Kiski watershed drips and dribbles iron and sulfur into the waters of the Kiski River. These molecules, then, begin to react both chemically and biologically as they flow along on their way to the Allegheny River.
Usually the water in the Kiski is brown and foamy. The transformation of this silty, frothy stream into Mountain Dew green occurs in the quiet, still sections of the river. Many of these still areas are often located just upstream from the old stone-piled, slack-water dams that were built back in the early Nineteen Century to make sections of this shallow river navigable for barges. The dams have tumbled into decay and at high water are difficult to see, but when water levels fall sufficiently (usually in mid to late summer) the remains of these dams back up broad pools that begin to warm and stagnate. Oxygen levels fall in the stilled water and relic microorganisms, released from the competition from more robust aerobic species and the directly toxic effects of dissolved oxygen begin to process the dissolved irons and sulfates in new ways.
One group, the sulfate reducing bacteria, are true anaerobes. They use sulfates as their final electron acceptors in energy metabolism and slowly crank out usable metabolic energy from the oxidation of dissolved organic molecules in the water. When they stick the spent electrons from their organic food sources onto the sulfates they generate sulfides (especially hydrogen sulfide) which radically changes the chemical environment of the river water.
Another group of bacteria, the photosynthetic, “purple” bacteria, respond to the build-up of the hydrogen sulfides. These bacteria need hydrogen sulfide as the hydrogen source for their unique form of non-green plant photosynthesis. As they use the hydrogen atoms (and the absorbed energy from photons of sunlight) to make sugars out of carbon dioxide they oxidize the sulfides back into elemental sulfur which can then further oxidize back into sulfates (and new sulfuric acids).
A third group of bacteria are sulfate oxidizers. They directly use electrons from the sulfates to run their energy metabolism. They also regenerate sulfides and may use oxygen or some other molecule (like nitrate, for example) as their final electron acceptors.
Backing up the river, then, and letting the waters settle and stagnate changes the environment significantly and generates new pathways for the sulfur molecule. Elemental sulfur (from the photosynthetic bacteria) is yellow. Sulfates (from the photosynthetic, “purple” bacteria) are green in solution, and the purple bacteria add their own array of blue and purple, light-capturing pigments to the mix until some shade approaching chartreuse is formed.
When the green water behind the rock dams flows over the old stone-dam piles it generates a vigorous line of choppy rapids that infuses oxygen into it. The green color is instantly lost and the brown returns. The fragile balance of the oxygen sensitive bacteria is disrupted and the colorful cycling of the irons and sulfurs is lost. This year’s early “greening” of the Kiski was re-set by a couple of big rainstorms, but a few weeks later the river water had warmed up and turned green again.
A great deal of work up and down the Kiski Watershed has gone into controlling AMD. The photo to the left is Roaring Run (an important Kiski River tributary). The results of these efforts are impressive. The Kiski and its tributaries now have a rich base of invertebrates and fish (the Roaring Run Watershed Association actually has a fishing contest on the Kiski each year!). I have seen hellgrammites (Dobsonfly larvae) in the Kiski and along the trails that follow it. Dobsonflies are a significant sign of environmental quality! I have also seen bald eagles regularly hunting up and down the Kiski.
The Kiski was once a rich, food producing resource highly valued by the Native Americans tribes who lived here and also by the early, European settlers who assumed ownership of the area. Paul Wallace in his book “Indians of Pennsylvania” describes the multiple Delaware and Shawnee villages along the Kiski, and T. J. Henry in his book “History of Apollo” describes piles of old mussel shells and camp fire remains in the plowed soil of area farms. He also describes with great exuberance a massive, communal fish hunt by settlers on the Kiski and the division of the piles and piles of fish among the participants.
The Kiski was once a place of abundance. The green, river pools of summer, though, tell us that there is still a great deal of iron and sulfur in its waters. We still have a lot of work to do to get it back to health.