LIGHT: It has more greenish shades, there is loss of bacteria in the surface layer that has become reddish and yellowish. Sulfur disappears and has CO2 bubbles, surface water is also transparent.
DARKNESS: It is grey more clear and surface water presents a layer of microorganisms from Brown.
DIFFERENCES: After eight weeks we observe that the bottle exposed to light presents more greenish coloration and a loss of black (iron sulfide). Finally, the surface water is clear and there is loss of microorganisms.
The dark bottle presents a gray color more clear and on the surface turbidity has been lost.
The layer you see at the surface in the dark column is interesting. Is it oily? People usually see such surface layers in nature and think it is an oil spill but actually are iron oxidising bacteria (Leptothrix) that are capable to attach themselves at the water-air interface. Next time you see this, you know! Check these cool pictures here. http://www.lindagrashoff.com/08252006-36.html
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