Just about three months ago, I set up a Winogradsky Column to see if I could recreate the environment that turned seashells black (see Winogradsky Column activity, June , 2010) Now, three months later, it is time to look at the results.
Just a quick recap of a Winogradsky Column - the column can be used to grow many types of bacteria, and it replicates an aquatic environment – either salt or fresh water.
Over a period of a few months, organisms should grow in the column.
- At the bottom of the soil where there is no oxygen, anaerobic bacteria will grow. These anaerobic bacteria produce hydrogen sulfide.
- In the water above the soil, there are algae cells that produce oxygen.
- As you descend in the sediment, the oxygen levels decrease and the hydrogen sulfide levels increase.
- Different bacteria grow best at different oxygen and hydrogen sulfide levels – causing a gradient of different bacteria from the top of the column to the bottom of the column.
- These different bacteria are of different colors – causing a gradient of colors in the column.
The columns sat on my desk where I could watch them and note the changes that occured as time passed. The columns started with black mud on the bottom - mud from a salt marsh. Above the mud was a layer of sand, a few inches of water and an air space. The water was an orange color because the finer particles of sand had not yet settled out.
After a few weeks, all of the sand and the water turned black, a clear indication that the anaerobic bacteria in the column were flourishing. Another indication of how well they were doing was the smell of rotten eggs that began to permeate my study. The bacteria were producing a good supply of hydrogen sulfide - a good sign for my experiment. At this time, I realized that the caps on the columns were not closed tight. I soon remedied that and the odor disappeared.
As time went on, I began to notice different colors in my columns. I now had a healthy growth of a number of different types of bacteria - each requiring different growth conditions that now occured in the columns.
After three months, my columns looked good. Both anaerobic and aerobic bacteria were growing in the column, but the big question was whether the environment I had created was turning seashells black. The idea is that seashells buried in an anaerobic environment that contains iron will be stained black by the iron sulfide that is created by the reaction of hydrogen sulfide from the bacteraia and iron in the sediment.
One of my columns contained iron in the form of nails added to the mud (the column on the right) , and one column had no nails. My hypothesis was that in the column with the nails, iron sulfide would be produced and that would stain the shell fragments black. In the column with no nails, the shells would remain white.
Now it was time to empty the column and look at the shell fragments. As you can see by the picture below, the shell fragments in the column with the nails are definitely darker than the other shell fragments. It would seem that the action of the anaerobic bacteria in the presence of iron produces iron sulfide will turn shells black
Of course, this experiment is only a beginning. Some questions that come to mind:
- How long will it take to turn the shells completely black?
- The shells in the column without nails did turn dark, although not as black as in the other column. If left them in the column longer, would they also have turned black?
- Did the mud I used have some iron in it to begin with?
- If I bury the shells in sand only where the presence of oxygen will prevent anaerobic bacteria from growing, will the shells still turn black?