Anyone that has spent time under the bluffs in the Bankhead National Forest has probably seen the bright orange stains that seem to seep out of the rock. The orange color is associated with iron-rich groundwater. The orange color is the result of dissolved iron in the water being oxidized by iron bacteria at the surface; it not a sign of water pollution. The naturally occurring iron bacteria change the colorless ferrous iron dissolved in the groundwater to a orange or rust-colored ferric form of iron. The ferrous form is somewhat soluble in water, while the orange ferric form is relatively insoluble. Deep in the earth, where oxygen and bacteria are not present, the c
olorless ferrous form is stable. But when this groundwater seeps out and is exposed to the oxygen in the air, the bacteria "feed" on the ferrous iron and derive energy from the chemical reaction. Where the iron-rich water seeps out of a rock, a soft orange deposit will build up at the site where these iron bacteria are working. Sometimes the deposits will build up over the years into mounds that look like soil.
Some more photos of iron bacteria in the Bankhead National Forest are located in this photo album. These iron bacteria deposits are seen in the Bankhead National Forest because layers of rock that are normally 70 feet or more underground are exposed at the base of these bluffs. Bluffs of this size are not common in other areas of Alabama. Groundwater in more shallow layers of rock and soil has usually been in contact with oxygen and bacteria before it comes to the surface. More information about
iron bacteria is located in wikipedia.
Anyone that has spent time under the bluffs in the Bankhead National Forest has probably seen the bright orange stains that seem to seep out of the rock. The orange color is associated with iron-rich groundwater. The orange color is the result of dissolved iron in the water being oxidized by iron bacteria at the surface; it not a sign of water pollution. The naturally occurring iron bacteria change the colorless ferrous iron dissolved in the groundwater to a orange or rust-colored ferric form of iron. The ferrous form is somewhat soluble in water, while the orange ferric form is relatively insoluble. Deep in the earth, where oxygen and bacteria are not present, the c
olorless ferrous form is stable. But when this groundwater seeps out and is exposed to the oxygen in the air, the bacteria "feed" on the ferrous iron and derive energy from the chemical reaction. Where the iron-rich water seeps out of a rock, a soft orange deposit will build up at the site where these iron bacteria are working. Sometimes the deposits will build up over the years into mounds that look like soil. Some more photos of iron bacteria in the Bankhead National Forest are located in this photo album. These iron bacteria deposits are seen in the Bankhead National Forest because layers of rock that are normally 70 feet or more underground are exposed at the base of these bluffs. Bluffs of this size are not common in other areas of Alabama. Groundwater in more shallow layers of rock and soil has usually been in contact with oxygen and bacteria before it comes to the surface. More information about iron bacteria is located in wikipedia.
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