It is easier to fill the bottle if you first remove the narrow neck of the bottle by carefully cutting through the plastic with a single-edged razor blade or paper cutter. Pour the water you have collected over the top of the sand-mud mixture so that there is a small amount of unabsorbed water on top. Cover the bottle with plastic film secured by a rubber band, place it in a sunny window, and a rich culture of photosynthetic bacteria will develop within a few weeks. A similar column kept in the dark will also develop a bacterial population, but the bacteria will not be photosynthetic. Watch the columns over several months.
Color changes indicate that ecological succession is taking place.
Discussion Questions Describe the changes you see taking place over a period of several months. Record observations every one to two weeks. Using a long pipette, take samples from various depths within your column and place them on a microscope slide. Examine and draw those that you see. Use a key to microorganisms to identify all you can.