In this activity, I want to see if I could recreate conditions at the beach, and stain seashells black (see this month’s Nature Story, “Someone Else’s Back Yard”). Here is how it is supposed to work:
In an estuary or marsh area, the sediment is very fine. At a certain depth under the sediment (sometimes only an inch below the surface), water is trapped and cannot be refreshed by fresh seawater. The oxygen in this sediment is soon depleted. Anaerobic bacteria – bacteria that live in oxygen depleted soil – abound. They give off hydrogen sulfide gas. This gas reacts with iron in the sediment, producing iron sulfide. The iron sulfide stains any shells buried in the sediment black.
To recreate these conditions in the lab (my kitchen), I built a Winogradsky column. Named after Sergei Winogradsky, a pioneering microbiologist, the column can be used to grow many types of bacteria, and it replicates an aquatic environment – either salt or fresh water.
In the column, the bottom two thirds are filled with soil. Water is then added to the column leaving the last 1/6th with air. The bottle is capped and put in a bright room, but not in direct sunlight.
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.
If the sediment in my column contains iron, the hydrogen sulfide from the anaerobic bacteria will react with the iron to produce iron sulfide that will stain seashells black.
Set up a Winogradsky column to grow anaerobic bacteria
Add iron (in the form of rusty nails) to the column.
Add pieces of seashell to the column.
Wait a few months for the process to develop the
check the color of the seashells.
Set up a second Winogradsky column without the nails.
Wait a few months for the process to develop then check the color of the seashells.
- 2 1-liter soda bottles with caps
- mud from an estuary (note: sediment can come from salt water or fresh water. Or you can just use sand.)
- strips of newspaper (carbon source)
- plant food (nitrogen and phosphorus)
- rusty nails
- water (fresh or salt)
- Chop up some newspaper and place it in the bottom of both bottles.
- Add a few rusty nails to the bottom of one of the bottles.
- Crush up some shells so the pieces will fit into the bottle. Add a few pieces of shell to both bottles.
- Fill both bottles about 2/3rds full of sediment. (For my column, I added 1/3rd of mud from a saltwater estuary and 1/3rd sand.)
- Fill half of the remaining space with water – either fresh or salt.
- Cap the bottles tightly.
- Place both bottles in a bright area, but not in the direct sun.
- Wait a few months, checking your bottles regularly for color changes.
- DO THIS STEP OUTDOORS: Empty out the contents of the bottles and check the color of the shells.
I have both columns on my desk in my study and will be watching them closely. I will report back in a few months to let you know how my experiment turned out.