On September 14, 2007, Reinhard Nitze saw intensely iridescent colours in some puddles on a lane near Barsinghausen/Egestorf (Lower Saxony, Germany). These were probably caused by bacteria of putrefaction coming from decomposing grains of wheat in the water, just as the colours showed up only in those puddles containing larger amounts of grains. The grains originated from the fields along the lane and had probably fallen from a trailer when the harvest was brought in.As some of the grains were already covered with green algae, they must have been lying in the water for some time already. Also remarkable was the rusty colour of those puddles which had already fallen dry.
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
Most of the cultivation pools in my room are now showing much smaller coronas than earlier. In each pool the corona is of constant size over the whole bacterial film surface, but from pool to pool their size vary.
Even though these coronas are smaller than before, they still are large as compared to pollen coronas. Unfortunately I have no photos for comparison.
In the composite image are two coronas photographed with same lens (not to scale with upper single image, which has been taken with zoom lens). The microphotograph of the bacterial film is from the smaller corona on the left.
The light source was a 50 W halogen spotlight that I made even more concentrated by placing the lamp in a cardboard box, into which a small hole was made for light to come through. When taking photos, the room was otherwise darkened.
[Posted by Marko Riikonen]
Some time ago Jari Piikki posted me a couple of drops of the surface film that produced his colourful corona. I mixed it in a bucket full of tap water with also some forest litter added. After a week or so there appeared a bluish film on water surface. Closer inspection with point-like light revealed more colors. It was actually a large corona, with blue inside, and green and red on the outer edge.
Only a segment of the corona could be seen in the small bucket. This is shown in the upper left image. Unlike the peculiar corona described by Piikki, this one has true blue aureole starting right from the reflection image of the lamp. Outside the blue some green and perhaps red maybe distinguished – visually these colors were clear. Upper right image is microphotograph of the film. It consisted of bacteria.
Day after taking the upper photographs the phenomenon in the bucket changed. Now there was similar corona as what Piikki photographed, only less bright. This is shown in lower left. There was no aureole, but instead a dark area surrounded the light source. This also was consistent with Piikki’s observation. Microphotograph of the film on this stage is shown on the lower right.
The most conspicuous difference in the bacterial level between the two stages is the crowding – there are more bacteria in the latter stage. Is this somehow related to the changes in the phenomena? Perhaps Minnaert can give an answer. In the chapter about coronas seen in windows, he describes how these coronas have an aureole replaced by dark area. He speculates the dark area forms because in the two dimensional plane of the window surface the droplets can be evenly spaced – a situation which can not happen when particles are freely floating in the air.
Now, if one looks at the lower right microphotograph, one can imagine that these bacteria indeed are spaced more evenly as compared to the upper photo. In the Piikki’s microphotograph, which looks like a maze, the bacterial film might consist solely on the long strands that are seen in small numbers also in my lower right photo. When packed next to each other, these kind of strands would possibly be very evenly spaced, thus perhaps contributing to the stronger corona. Piikki’s photograph is, however, too much out of focus to be sure of this interpretation.
The bacteria species could be Nevskia ramosa, which is well known neustonic (water surface inhabiting) bacteria. Genomic fingerprinting would be needed for confirmation. For the last note it should be said that the inverted colors between the two microphotographs are due to differences in focus. The upper image is a bit out of focus and thus the bacteria shows as dark spots.
[Posted by Marko Riikonen]
Jari Piikki have also found some ponds with algal films that show optical phenomena. The ponds were sampled and the alga allowed to breed for some weeks. Extracts were photographed through a microscope. In one pond, Botryococcus alga was abundant nine years ago but then disappeared. Now it is back and quite large Quetelet rings and a corona were visible. Another pond on one island possibly contained Chromulina rosanoffi and microscope images showed it floating on the water surface.
Jari Piikki also found a new optical phenomenon. He took (like Marko) some samples from ponds and cultivated them. In one of them Chromulina disappeared and some other alga appeared. There could be seen a very colourful ring with two zones of spectral colours around the reflection from the surface of the Sun or an artificial light. The ring was oval and became smaller, when the light was brought closer to the water surface. Its diameter in sunlight was about 30 degrees and the inside was dark, so it was not an aureole. also visible when the light shone through the alga from below. Many photographs of the surface were taken with a microscope to show its structure. You can see it in some photos. The alga constantly changes constantly and now shows small colourful blotches.
[Text: Jari Piikki]
Here are some results from the work I have done this summer on the phenomena caused by algal film on water surface.
The upper pair of photographs shows elliptical corona and the alga that caused it. Pine pollen gives the scale. This corona-type display has no other phenomena.
The lower photo shows another type of display, which exhibits Quetelet rings, brightenings around sun””s reflection image, glory and fogbow. In this case there is also unidentified diffuse feature marked with arrows. In addition, fogbow and glory have spot-like brightening towards nadir. Two B&W photos of the algae causing this type of display are shown. In the lower photo the algae are possibly turned 90° in comparison to upper, showing elliptical shape. This species might be Chromulina rosanoffii. It””s about 5-10 µm in size (not to scale with upper color photo) and well transparent to make glory.
These phenomena turned out to be common, at least this summer. They were most abundant on rocky Finnish archipelago islands, which harbour endless number of small rock pools.
[Posted by Marko Riikonen]