Experiment 1: The Winogradsky Column

QUESTION OF INTEREST:

What microorganisms can be found over time living in the ecosystem created in a Winogradsky column?

The Winogradsky column will demonstrate succession of microbial populations and changes in the environment brought about by certain microbial groups.

Samples collected from various sources (freshwater pond, salt marsh, compost pile, lake, river, field soil, forest soil, beach sand)
Amendments (newspaper, glucose or other sugars, leaves, other chemicals, etc.)
Glass or Plexiglas column (closed at one end)
Calcium sulfate or Sodium sulfate
Calcium carbonate
Distilled water
Analytical balance or another type of scale for weighing in grams
Beakers, jars or other containers for mixing

PROCEDURE:

1. Label the column with name and date.

2. Choose materials to use to pack the column and prepare them as a slurry having the consistency of a milkshake.  Materials may also be added by layers.

3. Weigh approximately 0.5 g of calcium sulfate or sodium sulfate per 100 g of sediment to be added to column and mix with sediment.

4. Weigh approximately 0.25 g of calcium carbonate per 100 g of sediment to be added to column and mix with sediment.

5. Remove twigs and other large debris from the slurry as they float to the surface.

6. Add any other chosen amendments to the sediment mixture.

7. Incubate the column where it will receive daylight or artificial light. You may choose the temperature at which to incubate the column.

8. Observe the column over the next several weeks for development of layers, smell, colors, zones, etc.

RESULTS:

Although each column is unique depending on its various soil composition, over a sufficient amount of time, patterns will emerge within the column.  The three major zones are as follows:  the aerobic zone, in which O₂ will diffuse in and out of the surface layer; the oxidized zone, consisting of nitrates, nitrites, sulfates, and oxidized iron; the reducing zone, consisting of ammonium, sulfide, and reduced iron.  Each of these zones hosts specific organisms (see figure).
 

CONCLUSIONS:

Examples of organisms that might be found in the aerobic zone include algae and cyanobacteria (prokaryoticphotoautotrophs).  The transition from aerobic to oxidized zone represents a microzone for the following organisms: chemoautotrophs (both nitrifiers and sulfur oxidizers).  In the oxidized zone, heterotrophs dominate including the denitrifiers and sulfate reducers. In addition, fermenters may also be found in this zone.
In the reducing zone, anaerobic conditions dominate. Anaerobic photoautotrophs and chemoautotrophs are residents as well as sulfate reducers, methanogens, and the ever-present fermenters.

MODIFICATIONS: for K-8 modifications

EXTENSIONS:

As a variation, one could construct several columns of the same bacterial recipe. A Dremel tool may be used to bore slots in plexiglas columns, allowing contact slides to be imbedded.  These slides should be sealed into the slots with a silicon sealant.

Removing and harvesting these slides at different time intervals can represent the shift in bacterial populations that occur in the column over time.

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