Rust color in the creek by Scroggs

I got an answer to the quesiton I raised about the rust-colored sediment in the creek that runs to the west of the garden and fields behind Scroggs. In fact, Dave ALMOND of Chapel Hill Stormwater Management came out and took a look. Very impressive! See below for full text of his report.....

The link form this page is to a good discussion of what he says it is - iron bacteria! It poses, it seems, no risk to anyone, and frequently happens around here.

The relevant portion is this:

"Description.


Iron Bacteria (Ferrobacillus, Gallionella, Thiobacillus, Leptothrix and Sphaerotilus) are a group of small (0.5 to 1.5 um), unicellular, organisms which grow in chains and excrete a mucilaginous sheath. (Image 1) This sheath becomes light brown from iron oxide (Fe (OH)3) and appears as a fuzzy coating on any available substrate (Image 2). Iron oxide is formed as the bacteria oxidizes ferrous iron (Fe2) to ferric iron (Fe3). The ferric iron becomes iron oxide when it is exposed to air (O2) and water (H2O). It is the oxidation of ferrous to ferric that produces the energy needed for the bacteria to survive. This makes them autotrophic, or self feeding, as opposed to heterotrophic. Heterotrophic organisms require a food source produced by others, like animals do.

Ecological Implications:

Iron Bacteria can be found in streams, lakes, ponds and ditches throughout the North Carolina. They are indicative of iron rich water, ground water seeps and low flow conditions. These waters are often acidic or in contact with an anaerobic sediment layer because ferrous iron is favored in these conditions. Although unsightly, Iron Bacteria are not known to pose any environmental or human health risk."
If anyone sees anything in the streams that could constitute a spill or other pollution, it is his office that should be called - 969-RAIN or 969-7246.

If anyone wants to rely on Wikipedia, here is its entry on the subject.

Dave ALMOND's e-mailed report:

"I checked on the discharge at Scroggs Elementary and it is a large colony of iron-fixing bacteria called Gallionella ferruginea. These colonies occur when you have groundwater flowing through iron-rich soils or in areas where there is prolonged inundation or saturation of iron-rich soils. When the anoxic groundwater carrying iron particulates mixes with the oxygenated surface water, conditions are right for Gallionella to convert the soluble ferrous iron(Fe2) into insoluble ferric iron (Fe3). The bacteria form helical chains of ferric hydroxide as they convert the iron, so the combination of bacteria colony and flocculated helical chain byproduct forms a rust colored voluminous mass. There is no spill at this location, these are naturally occurring conditions.
Dave Almond

Stormwater Technician
Stormwater Management Division
Town of Chapel Hill
405 Martin Luther King, Jr. Blvd., Chapel Hill, NC
(919)969-2042
dalmond@townofchapelhill.org"