Thin film interference on the water surface

In the city of Lahti there is a landfill hill from which base in some places flows iron rich water. The bottom of these ditches is rusty brown and water has a strong iron smell. In some locations the water surface is completely covered with a film that displays spectacular colors in cloudy weather. This film is caused by iron oxidizing bacteria. The bacteria itself resides in the water, but it produces on the water surface substances from which it hangs down like a chain of sausages. Iron oxide is one of these products and it may be the cause of colors.

Author: Marko Riikonen

Posted on May 15, 2011, in observations, pollen and algae phenomena and tagged , . Bookmark the permalink. 3 Comments.

  1. Noli said…

    Might these bacteria be magnetotactic? I””ve read about some types of iron oxydizing bacteria also being “magnetic”, as they produce tiny chains of magnetosomes (magnetic intracellular bodies) inside their cells and they orientate following the magnetic field of Earth. These bacteria also produce a lipid layer around their magnetosomes, so the bacterial film might be the result of dead bacteria that””s cells are broken up so the membrane lipid of the magnetosomes got free?
    The magnetic bacteria are living at lower regions of water, not on the surface.

  2. Marko Riikonen said…

    Anything is possible. There is very little information to be found of this subject. I changed emails with Paul Doss, who has made research on these bacteria. According to him the beautiful thin film interference on the water surface photographed by Rick Mark is originated by Leptothrix bacteria:
    and it is a film of ferrihydrite that causes the colors (Minnaert also mentions the possibility of ferric origin for colors on water surface).

    The film presents often also a prominent metallic hue, in some places it is shining like gold, which lipid layer might not display. I have paid attention also to oil on water surface. The colors are always mediocre and oil film yields when disturbed. The films shown here crack and wrinkle at a slightest disturbance.

    Well, lets give the address again:

  3. I see this type of rainbow coloration all the time in the Adirondack Mountains. In my case it is when sap from balsum fir trees falls onto the water surface. Peter A. Siver

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