The Winogradsky Column — Build an Ecosystem in a Jar
One of the most fascinating biology experiments does not happen in a few minutes. It develops slowly over weeks as an apparently ordinary container of mud turns into a miniature microbial world.
Most school practicals are designed to give results within a lesson. Add one chemical to another and something changes colour. Connect a circuit and take a reading. Put a specimen under the microscope and observe it.
The Winogradsky column is completely different.
You build it, put it somewhere with suitable light, and wait.
At first, it looks like nothing more exciting than muddy water in a transparent container. A week later it may still look unimpressive. But gradually the column begins to change.
Dark regions appear.
Green patches develop.
Purple, reddish, orange or other coloured bands may emerge.
The surface may become greener.
What you are watching is not simply mud changing colour. You are watching different microbial communities establish themselves in different chemical environments.
That makes the Winogradsky column one of the best demonstrations I know of for showing what an ecosystem really is.
It is also a direct descendant of the work of Sergei Winogradsky, one of the founders of microbial ecology. His research helped establish the idea that microorganisms drive major chemical transformations in nature, including parts of the sulfur and nitrogen cycles, and that some organisms can obtain energy from inorganic chemicals rather than from light or organic food.
Time: noticeable development may begin over roughly 4–12 weeks, although columns can continue changing for many months and even longer.
Family appeal: ★★★★★
Why This Experiment Is So Good
There are experiments that demonstrate one scientific idea very clearly.
The Winogradsky column demonstrates many ideas simultaneously.
It can lead naturally into discussions about:
- ecosystems;
- microorganisms;
- photosynthesis;
- aerobic respiration;
- anaerobic respiration;
- fermentation;
- decomposition;
- food webs;
- competition;
- niches;
- nutrient cycles;
- sulfur chemistry;
- oxygen gradients;
- carbon cycling;
- succession;
- energy transfer;
- environmental change.
But perhaps its greatest strength is that it challenges one of the ways we tend to think about ecosystems.
When we say "ecosystem", students often imagine a woodland, pond or tropical rainforest.
Yet an ecosystem does not have to contain trees, deer, fish or insects.
A few centimetres of mud can contain an extraordinarily complicated community of organisms interacting with one another and modifying their environment.
Winogradsky columns are still used as teaching tools precisely because they allow changes in microbial communities and microbial metabolism to become visible on a human scale.
Who Was Sergei Winogradsky?
Sergei Winogradsky was born in 1856 and became one of the pioneers of microbiology.
His importance lies partly in changing the way scientists thought about microorganisms.
Microbiology had understandably become strongly associated with disease. Scientists such as Pasteur and Koch were demonstrating that microorganisms could cause fermentation and disease.
Winogradsky became interested in a different question:
What are microorganisms doing in the environment?
He studied organisms involved in sulfur transformations and later investigated nitrification. His work helped establish the concepts of chemolithotrophy and microbial participation in the great chemical cycles operating through soil, water and the atmosphere.
This was an enormously important change of perspective.
Microorganisms were not simply things that made us ill.
They were — and are — fundamental components of the Earth's chemistry.
Building a World Rather Than Growing a Single Organism
The philosophy behind a Winogradsky column is rather different from the traditional Petri dish.
On a Petri dish, we often try to isolate microorganisms.
In a Winogradsky column, the interesting feature is the community.
Different organisms alter their surroundings. Those changes then make conditions more favourable or less favourable for other organisms.
One organism's waste product may become another organism's raw material.
That is ecology.
And it happens inside the jar.
The Basic Idea
A typical column contains waterlogged sediment together with sources of carbon, sulfur and other nutrients.
Educational versions have used cellulose-containing materials such as paper as a carbon source and sulfate salts as a sulfur source. Different recipes produce somewhat different communities, which is itself an interesting experimental variable.
The material is placed inside a tall, transparent container and left somewhere well illuminated.
Then we allow biology to take over.
For a home demonstration I would favour a transparent plastic container rather than a large glass vessel, particularly where children are involved.
I would also put it inside a tray or secondary container.
And then I would leave it alone.
An Important Safety Point: Closed Does Not Mean Pressure-Tight
I would treat this primarily as a sealed observational experiment.
By that I mean:
build it, cover it, observe it and photograph it — but don't routinely open it and start culturing whatever you find inside.
There is, however, an important distinction between being closed to handling and being hermetically pressure-sealed.
Microbial metabolism can produce gases. Educational protocols therefore use suitable covered arrangements rather than assuming every container should be rigidly sealed against gas release. One University of Waterloo procedure, for example, describes clear film or a loosely closed lid.
Unknown environmental microorganisms also deserve respect. Published university work involving opening columns, isolating microbes and growing them on plates used formal biosafety procedures because the identities of the organisms were unknown.
For a family observational version, therefore:
- use ordinary natural sediment rather than sewage, manure or obviously contaminated material;
- wear gloves while assembling it;
- wash hands afterwards;
- keep it away from food preparation areas;
- don't sniff the contents;
- don't encourage children to open it;
- don't attempt to culture organisms from it at home;
- use a suitable covered container that cannot develop dangerous pressure;
- supervise children throughout its construction.
Once built, the interesting science can be done almost entirely through the wall of the container.
Where Does the Mud Come From?
This is another opportunity to introduce some real ecology.
Sediment from a pond, stream margin or other waterlogged environment already contains an enormous microbial community.
We are not really "adding bacteria" to our experiment.
They are already there.
What we are doing is changing their environment so that particular organisms become more successful than others.
That distinction matters.
The coloured bands are therefore an example of selection by environmental conditions.
What Happens During the First Few Days?
Probably nothing very exciting — at least nothing obvious.
And I rather like that.
Modern classroom science can sometimes give students the impression that experiments must produce immediate results.
Real biological research frequently involves waiting.
During the early stages, microorganisms begin consuming available organic materials. Oxygen in the deeper sediment becomes depleted because oxygen enters predominantly from above while microorganisms within the sediment consume it.
The result is one of the crucial features of the experiment:
An oxygen gradient develops.
There is relatively more oxygen towards the upper part of the system and much less oxygen deeper in the sediment.
That immediately creates different habitats.
Microorganisms that need oxygen have an advantage in one region.
Organisms capable of living without oxygen become successful elsewhere.
The column has started creating ecological niches. Winogradsky columns are specifically useful because chemical gradients such as these allow different metabolic communities to establish themselves in different regions.
Aerobic at the Top — Anaerobic Below
This provides a beautiful way of introducing the difference between aerobic and anaerobic metabolism.
At the top, oxygen can enter from the air and oxygen-producing photosynthetic organisms may also contribute.
Deeper down, oxygen can become extremely limited.
Yet life does not simply stop.
Different microorganisms can use completely different metabolic strategies.
Some ferment organic matter.
Others carry out forms of anaerobic respiration using substances other than oxygen as terminal electron acceptors.
Sulfate reduction is particularly important in many Winogradsky columns.
This can lead to hydrogen sulfide being produced in deeper anaerobic regions. Higher in the column, other organisms can exploit reduced sulfur compounds as energy sources. Winogradsky's own historical work on sulfur-oxidising bacteria helped establish the concept of chemolithotrophy.
Suddenly GCSE respiration has become microbial ecology.
Light Comes From One Direction, Too
Oxygen is not the only thing forming a gradient.
There is also light.
Light entering the container is most readily available close to its surface.
Photosynthetic microorganisms can therefore establish themselves where there is sufficient light — but different photosynthetic microbes have different chemical requirements.
Some thrive where oxygen is available.
Others occupy illuminated but oxygen-poor regions.
The result can eventually be visible bands.
This is one reason a Winogradsky column can become surprisingly beautiful.
What Do the Colours Mean?
This is where we need to be scientifically careful.
It is tempting to look at a purple band and announce:
"Those are definitely species X."
That would be going too far.
Different microbial groups can create characteristic colours, but colour alone is not sufficient to identify a species. University investigations that wanted proper identification used techniques including microscopy, biochemical testing and 16S rRNA sequencing.
For an observational experiment, therefore, I would use language such as:
"This colour may indicate that a particular type of photosynthetic or sulfur-metabolising microbial community has become established here."
Possible observations include:
Green regions
These may be associated with photosynthetic microorganisms, including algae, cyanobacteria or various photosynthetic bacteria depending upon their position and conditions.
Purple, red or pink regions
These can be associated with groups of anoxygenic photosynthetic bacteria.
Dark or black sediment
This often indicates strongly reducing conditions and sulfur chemistry occurring within the sediment.
Pale or whitish bands
Sulfur-oxidising organisms can sometimes produce conspicuous regions near interfaces where reduced sulfur compounds and oxygen meet.
But the important observation is not simply the colour.
It is where the colour occurs.
That tells us something about the environmental conditions preferred by that community.
The Most Interesting Place May Be the Boundary
One of the wonderful lessons from the column is the importance of interfaces.
Imagine a microorganism that requires a reduced sulfur compound coming from below but also needs oxygen coming from above.
Too high and there may not be enough sulfide.
Too low and there may not be enough oxygen.
There is therefore a relatively narrow region where both requirements can be satisfied.
Winogradsky's studies of the sulfur bacterium Beggiatoa were important in understanding organisms living around precisely this type of chemical interface.
This idea appears throughout biology.
Life often concentrates at boundaries.
River banks.
Shorelines.
Soil surfaces.
Lake sediments.
Hydrothermal vents.
Even the surfaces of our own bodies.
The Column Is Creating Its Own Environment
Perhaps the most important concept in the whole experiment is this:
Organisms do not simply respond to their environment. They change it.
A microorganism consumes one chemical.
It releases another.
That chemical diffuses into a neighbouring region.
Another organism uses it.
Its metabolism produces something else.
That product becomes available to another population.
And gradually a network develops.
This is what makes the column much more than a jar containing microbes.
It is an ecosystem.
Decomposition Becomes Visible
Put a piece of dead leaf into a pond and eventually it disappears.
We often simply say that it "rots".
But that one word hides enormous biological complexity.
Organic material contains carbon compounds that can potentially provide energy and raw materials for microorganisms.
Decomposers break complex materials down.
Other organisms exploit the resulting substances.
Carbon is transferred.
Mineral nutrients are released and transformed.
Gases may be produced.
The chemistry of the environment changes.
The Winogradsky column gives us a model in which we can discuss all of this.
The Sulfur Cycle in a Jar
The sulfur cycle is rarely as familiar to students as the carbon cycle.
Yet here we can see the consequences of sulfur transformations occurring within centimetres of each other.
In oxygen-poor regions, sulfate-reducing microorganisms can convert oxidised sulfur compounds into more reduced forms.
Those reduced sulfur compounds can move towards regions where other organisms oxidise them again.
Winogradsky's work helped establish microbial sulfur cycling as an important ecological process.
This makes the column especially useful at A level.
It shows that a nutrient cycle isn't merely a diagram with arrows.
Each arrow represents chemistry.
And very often a microorganism is responsible for making that chemistry happen.
Competition Without Seeing a Single Individual
There may be billions of microorganisms in the column, yet we cannot see an individual bacterium with the naked eye.
Nevertheless, we can observe the consequences of competition.
Suppose one group of organisms grows particularly successfully in a particular region.
It consumes resources.
It changes the pH.
It changes oxygen concentrations.
It creates waste products.
Those changes affect everything around it.
Another group may become more successful as a consequence.
Another may decline.
Ecology is taking place before our eyes even though the individual organisms are microscopic.
Turn It Into a Proper Investigation
The temptation is simply to make one column and admire it.
That is perfectly worthwhile.
But we can make the experiment much more scientific.
Photograph it every week
Put the column in approximately the same position, with the same background and lighting.
Take a photograph.
After several months you will have a wonderful time-lapse record.
You can compare:
- week 0;
- week 2;
- week 4;
- week 6;
- week 8;
- week 12.
You may see changes that were almost impossible to notice from day to day.
Measure the Bands
Place a ruler beside the outside of the column.
Without opening anything, record:
- where each band begins;
- where it ends;
- its thickness;
- its colour;
- how it changes over time.
You could create a simple results table:
| Week | Observation |
|---|---|
| 0 | Uniform brown sediment |
| 2 | Darkening in lower sediment |
| 4 | First coloured patches visible |
| 6 | Distinct bands developing |
| 8 | Bands becoming stronger |
| 12 | Several distinct microbial zones |
Your actual results may of course be completely different.
And that is part of the fun.
Make Two Columns
This is where it becomes a genuine experiment.
Use sediment from the same source.
Make two otherwise similar columns.
Then change one variable.
For example, a properly supervised investigation might compare different nutrient additions or different light conditions. University teaching exercises have used control and experimental columns specifically to investigate how changing the chemical environment alters microbial communities.
Now ask:
What do we predict will happen?
That word — predict — changes the activity from demonstration to investigation.
Light and Dark
One particularly interesting question is:
How important is light to the development of the visible communities?
Two comparable columns could be maintained under different illumination conditions while other variables are kept as similar as practicable.
Then photograph them at regular intervals.
Do the same bands appear?
Do they develop at the same rate?
Are some colours missing?
Why?
Immediately we have moved into experimental design.
Independent variable: light conditions.
Dependent variable: observable development of microbial regions.
Control variables might include:
- sediment source;
- container dimensions;
- nutrient additions;
- temperature;
- amount of sediment;
- amount of water;
- duration.
That makes it relevant not just to microbiology but to how scientists design experiments.
GCSE Biology Connections
For GCSE students, I would use the column to reinforce several familiar concepts.
Ecosystems
An ecosystem consists of organisms interacting with each other and with the physical environment.
Here the physical environment includes:
- oxygen concentration;
- light;
- nutrients;
- water;
- chemical compounds.
Decomposition
Microorganisms break down organic material.
Respiration
Different organisms can obtain energy under different environmental conditions.
Photosynthesis
Photosynthetic microbes require suitable light but do not all occupy exactly the same ecological niche.
Competition
Organisms compete for resources and occupy niches where they are best adapted.
Nutrient cycling
Atoms are repeatedly transformed and reused rather than simply disappearing.
A-Level Biology Connections
At A level the discussion can go considerably deeper.
We can introduce:
- redox reactions;
- electron donors and acceptors;
- facultative and obligate anaerobes;
- fermentation;
- sulfate reduction;
- chemolithotrophy;
- photoautotrophy;
- anoxygenic photosynthesis;
- diffusion;
- ecological succession;
- biogeochemical cycles;
- microbial community structure.
This is where an apparently simple jar of mud becomes extraordinarily sophisticated biology.
It Also Teaches Patience
There is another lesson here that does not appear on many examination specifications.
Science does not always happen immediately.
I think that is valuable for children to experience.
For the first few days, they may ask:
"Has anything happened yet?"
Probably.
But we can't necessarily see it.
Then one day somebody notices a patch that wasn't there before.
A week later it is stronger.
Another region appears.
Eventually the jar begins to look completely different.
The experiment rewards observation.
And patience.
Keep a Winogradsky Diary
I would encourage a child or student to keep a simple notebook.
Each week record:
Date
Photograph number
Colours visible
Position of bands
Any bubbles or other visible structures
What has changed since last week?
What do I think will happen next?
The last question is especially important.
A prediction forces the observer to think about the science rather than simply describe what they can see.
What If Nothing Happens?
That is also science.
A Winogradsky column isn't a commercially manufactured demonstration designed to guarantee exactly the same coloured stripes every time.
It contains a natural community.
Different sediment contains different microorganisms.
Temperature differs.
Light differs.
Nutrient concentrations differ.
The initial chemistry differs.
Consequently different columns can develop differently.
Published teaching work has deliberately exploited this flexibility, using columns to investigate how environmental changes alter microbial communities.
Rather than saying:
"My experiment failed."
Ask:
"Why did my column develop differently?"
That is a much more scientific question.
Don't Be Tempted to Open It
Once colourful colonies appear, the obvious temptation is:
"Can we take some out and look at them?"
For a family experiment, my answer would be no.
Once we start isolating unknown environmental microorganisms, growing cultures and handling samples, we have moved into a different type of microbiology.
University researchers doing this with Winogradsky columns used laboratory biosafety practices because the organisms being isolated were initially unknown.
Fortunately, we do not need to open the container to learn from it.
The ecological patterns are the experiment.
A Living Model of Planet Earth
There is a rather wonderful wider lesson hidden inside the column.
Much of Earth's biosphere is microbial.
Microorganisms transform carbon.
They transform nitrogen.
They transform sulfur.
They alter oxygen concentrations.
They break down dead organisms.
They interact with plants and animals.
And they have been doing many of these things for immense periods of geological time.
Winogradsky's great contribution was recognising that microorganisms needed to be understood not only as isolated laboratory cultures but as participants in complex natural communities and chemical cycles.
The column bearing his name captures that idea beautifully.
Why I Like This Experiment So Much
There are certainly more dramatic experiments.
Nothing explodes.
Nothing suddenly changes colour in five seconds.
There isn't an exciting reading flashing up on a digital sensor.
Instead, you put some mud in a transparent container.
And wait.
But that is exactly why I like it.
Over several weeks an invisible biological community gradually reveals itself.
Different populations occupy different regions.
Chemical gradients develop.
Microorganisms alter their surroundings.
Other organisms exploit those changes.
Carbon and sulfur move through the system.
Light supplies energy to some communities while chemical reactions provide energy to others.
Eventually you realise that you aren't looking at dirty water at all.
You are looking at a landscape.
The distances are measured in centimetres rather than kilometres, and most of its inhabitants are microscopic, but ecologically it contains many of the same principles that operate in a lake, salt marsh, soil profile or ocean sediment.
Conclusion — An Ecosystem That Builds Itself
The Winogradsky column starts with one of the least impressive pieces of scientific apparatus imaginable:
a transparent container full of mud.
Give it nutrients, water, microorganisms, suitable light and time, however, and something extraordinary begins to happen.
Different regions develop different chemical conditions.
Different organisms exploit them.
Those organisms modify their surroundings.
Other organisms respond.
Communities form.
Competition takes place.
Materials are recycled.
An ecosystem emerges.
And all of this can be observed without ever seeing an individual bacterium.
For parents looking for a science project that lasts longer than an afternoon, and for students wanting to see GCSE or A-level ecology transformed from textbook diagrams into something living, I think the Winogradsky column is difficult to beat.
Build it today. Photograph it every week. Then let the microorganisms tell the story.
