Winogradsky

The pictures above are of the spectacular Winogradsky column produced by a lab in 2000. Even though everyone starts with the same materials, the columns can turn out very differently depending on the bacteria that may or may not be present, and how well the amendments are mixed into the river muck.

This year was the first time that we've seen leeches in the columns, though I collected the river muck from the same location last year! I was unsuccessful in removing them from the columns, because they would hide in the muck whenever I reached in with forceps....

	The upper layers of the water in the column will harbour algae and cyanobacteria because it is an aerobic environment, and the oxygen produced by photosynthesis in these organisms keeps it that way.
	Below this layer, you can observe a bright red layer at the sediment/water interface. This is caused by the purple nonsulfur and purple sulfur bacteria. They both can use hydrogen sulfide as an electron donor, but the purple nonsulfur bacteria are much less tolerant to high concentrations of H₂S and will usually appear higher up in the column compared to the purple sulfur bacteria. The purple nonsulfur bacteria are also facultative with respect to oxygen while the purple sulfur bacteria are mostly strictly anaerobic.
	Under the red layer, the green sulfur bacteria can be found. They are obligate anaerobes which perform anoxygenic photosynthesis. They utilize H₂S as an electron donor, and are much more tolerant to sulfide than the purple bacteria. This is why they are often found below the purple bacteria in the column, although often both the purple and green bacteria are seen as patches of growth rather than a distinct layer.
	The anaerobic sediment layer will contain the sulfate-reducing bacteria that convert sulfate to sulfide which diffuses up through the sediment layers and is utilized by the purple and green sulfur bacteria. The presence of sulfide in the column is obvious from the smell - rotten eggs!