By Dr. David Wartinbee, for the Redoubt Reporter
Photos courtesy of Dr. David Wartinbee. A layer of iron-rich water seeps out of the Kenai bluff. The yellow deposits are created by bacterial growth. On closer examination, an oily sheen can be seen to the left, caused by breakdown of dead iron bacteria.
As the day warmed up and the winds died down, it seemed like a great time for an afternoon walk along the beach in Kenai. The incoming tide and the remaining ice boulders along the shore forced me to walk close to the steep bluff.
In a number of places it looked like there were giant orange icicles painted on the cliff. They appeared in several places, and many seemed to start at a particular layer of rock or sediment. In some places the shiny orange areas were also tainted with what looked like an oily sheen. Is there something bad going on here?
Well, not really. What I was seeing was the perfectly natural result of masses of bacteria and their metabolic waste products.
The colored material is ferric hydroxide, or ferric oxide, and is commonly referred to as “yellow boy.” This stuff can be bright yellow, orange, dark red or even brown in color. It is insoluble in water that has a near-neutral pH, so it precipitates out of solutions.
The way yellow boy is formed involves a number of chemical changes that often are promoted by special bacteria. Most water has a small amount of iron dissolved in it. When the water is deep underground, it probably has no contact with oxygen so the common form is ferrous iron. When the water comes to the surface where oxygen is present, such as along a particular stratum of the bluff, the reactions begin. Iron atoms lose an electron (they are oxidized) and are converted into ferric ions. Then these ferric atoms form oxides of iron with the oxygen atoms. Ferric iron compounds were the brightly colored deposits I found.
There are a number of bacteria that use these oxidizing reactions to gain energy. We do a similar thing when we eat a candy bar, our bodies gain energy by breaking down the sugars. When we break down sugar, our metabolic waste product is carbon dioxide. When these bacteria finish their metabolism, their metabolic waste products are ferric iron compounds. These common bacteria can be in the genus Leptothrix, Conothrix, Gallionella or Ferrobacillus.
The iron bacteria often grow in long filamentous forms, while others have frequent branches in their filaments. Bacterial strands then trap the yellow boy into colorful and gelatinous-looking masses. If we put a pinch of this colorful material under a microscope, the bacteria are readily visible among the yellow ferric oxide compounds.
The oily sheen that is often seen with the yellow boy masses may look like an area where motor oil was spilled. However, this sheen results from the breakdown of dead iron bacteria. These colorful areas are created by huge numbers of bacteria, and bacteria don’t live very long. So wherever we see the ominous-looking oil sheen, it is a reminder of how the colorful material was created.
None of these bacteria are pathogenic and their waste products are pretty much nontoxic. However, they can take up residence in wells and water systems where they can cause problems. Yellow boy stains may only be considered unsightly but their filamentous masses of bacteria can clog filters. There are some reports of altered tastes in water or in drinks made with the water.
Bacterial growth in an area where iron-rich waters seep out of the Kenai bluff. On closer examination, the yellow masses appear to be almost slimy due to the bacteria masses where the water trickles along.
Sometimes another group of organisms called sulfur bacteria grow alongside the iron bacteria. When this happens, black deposits can be formed and there can be a release of hydrogen sulfide. Hydrogen sulfide is the cause of a “rotten egg” odor in water.
There are a variety of treatments for wells with iron bacteria and I would advise contacting a water specialist. A common but often short-lived fix is the use of bleach in the well, since it will kill most bacteria it contacts. However, there are some serious complications due to required flushing before drinking the water. Again, contact a specialist if you have a water system with iron bacteria issues.
These reactions and formations of yellow boy have created disastrous problems in many parts of the eastern United States. When sulfur compounds are exposed during coal-mining operations, various sulfuric acids are formed. The water then becomes acidic and iron atoms are oxidized into ferric ions.
Through natural formation and iron bacteria assisting the reactions, huge amounts of yellow boy are formed. Because of the acidic conditions, the yellow boy remains in solution much farther downstream. When yellow boy finally precipitates out, it covers everything with thick layers of brightly colored ferric oxides. That in turn smothers the aquatic organisms and all their food resources. Essentially, the acidity and yellow boy deposits sterilize the stream. Trout streams in coal-producing states have been turned barren by the formation of yellow boy.
We can find iron bacteria growths along the Kenai bluffs, as well as along many of our local streams. Fortunately, the amount of iron coming to the surface is small and the amount of yellow boy being formed is equally small.
Next time you come across one of these colorful growth areas you’ll know that bacteria are hard at work oxidizing iron and creating colorful deposits of yellow boy.
David Wartinbee, Ph.D, J.D., is a biology professor at Kenai Peninsula College’s Kenai River Campus. He is writing a series of columns on the ecology of the Kenai River and Cook Inlet watershed.