Ecosystem in a Bottle:
Is it Sustainable?
Challenge: Create a self sustaining pond ecosystem in 2 weeks. Sustainability will be
determined by measurements and observations that indicate your pond has habitable
conditions that are maintained. In other words positive equilibrium is reached. If you are
able to maintain sustainability you will add a fish to your system. Provided your system
demonstrates stability with the fish in the system, the fish is yours to take and raise at
home.
Documenting change
For two weeks you will be observing your ecobottle for changes that take place. Life itself
can create change in an ecosystem. Sometimes change can be beneficial and sometimes it
can create unsustainable conditions. Making good observations and measurements will
allow you to best assess the changes occurring.
Create a data table using Numbers. This data table will be used to collect, organize and
analyze the observations and measurements you take over the next two weeks. Be sure you
save your data because you will pass it all in at the end of this investigation. You must do
daily observations and DO (except on Saturday, Sunday and holidays) and collect
temperature, pH, and ammonia on the days that class meets. You might consider drawings
or photos to help support your written observations. You can use your laptop camera.
Detailed observations make it easier to understand the changes that have occurred.
Make the following observations: Date, time of day, water level, if you added water and
how much, change in water color, change in odor, change in animal life, change in plant life,
clarity of the water or change in clarity, change in abiotic factors (temperature, dissolved
oxygen, pH, and ammonia) and any other factors you may notice or feel are important.
Creating Your Ecobottle
Materials
Pond Water
Pond Organisms (animals)
Pond Organisms (plants)
Measurement kits (see list)
Set Up
In Class
Clear, 2L soda bottle
Sharpie
Gravel
Scissors or box cutter knife
1. Plan - Decide what plants and animals to keep in your aquatic ecosystem, and what
you might select as a test variable.
2. Prepare Bottle – cut the top spout from the bottle leaving as much height as
possible.
3. Gravel - Place 2-3 cm of gravel in the bottom of the container.
In the Field
4. Water. Obtain pond water from school pond. Must have enough to fill your bottle
and more for later. (Yes the water will be murky and perhaps a little stinky).
5. Plants and Animals – Collect any organisms from the ponds that you would like to
include in your bottle. There are frog and newt tadpoles, snails, water insects,
leaches, duck weed, etc. NO EGGS MAY BE COLLECTED!!!! Think about the
organisms that you want to live together in your system. Place the plants and animals
carefully into the container.
Back in the Class
6. Water Level. Pour the pond water into your bottle to about 1 cm from the top. Mark
the water level with a sharpie.
7. Label your bottle with your name for easy identification.
8. Consider where to place ecobottle - Temperature. As water warms up, it contains
less oxygen. Keep your experiment in a cool environment out of direct sunlight will
help if from getting too warm and hold oxygen BUT sunlight is needed for
photosynthesis to produce oxygen.
9. Record Initial Set of Data – measure and record your first full set of data to
document the starting conditions for your bottle.
Procedures for Measurements
Temperature
Procedure:
Place rinsed and dry thermometer into water. Do not measure with full sun shining on
the thermometer. Move bottle out of sun. Wait until temp stabilizes (2-3 minutes).
Read in C. You can also use the temperature probes that interface with your laptop.
Why measure?
Water temperature is one factor that determines which species may or may not be
present in an environment. Temperature affects feeding, reproduction, and the
metabolism of aquatic organisms. Not only do different species have different
requirements, but optimum temperatures may change for each stage of life. Fish larvae
and eggs usually have narrower temperature requirements than adult fish.
All species can tolerate slow, seasonal changes better than rapid changes. Thermal
stress and shock can occur when temperatures change more than 1 to 2C in an hour.
Consider measuring temperature at different times of the day.
Procedure:
pH
Use pH indicator paper. Dip a new piece of paper into a sample from your ecobottle.
Compare the color of the paper strip to the indicator colors provided. Be sure to keep
strips dry until use.
Why measure?
pH is a measurement of the activity of hydrogen ions in the water. pH measurements
run on a scale of 0 – 14 with 7.0 considered neutral. Liquids below 7.0 are considered
acid, those between 7.0 and 14.0 are designated bases or alkaline. The scale is
logarithmic which means that for each one-unit change in pH actually represents a tenfold change in acidity or alkalinity. In other words, pH of 6.0 is 10 times more acidic
than a pH of 7.0. A range of pH 6.5 to 8.2 is optimal for most aquatic organisms. When
plants are photosynthesizing they remove CO2 from the water and this can significantly
increase pH levels (make it less acidic).
There are also indirect effects. Toxic metals trapped in sediment are released into water
at lower pH levels. Toxicity of ammonia varies tremendously within a small pH range.
Dissolved Oxygen
Procedure:
Use Ms. Murphy’s laptop with the DO sensor connected to it. Unscrew the probe from
the plastic storage bottle. Place probe in ecobottle. Gently swirl probe in water until
the reading stabilizes. Rinse sensor with distilled water and return to storage bottle.
Why measure?
Like land organisms, aquatic animals need oxygen to live. They use oxygen dissolved in
water. Oxygen dissolves into water from the air or from plants photosynthesizing in the
water. This oxygenated water needs to move in order to distribute oxygenated water.
Water temperature can affect DO levels. Warmer water tends to hold less oxygen. DO
levels below 3 mg/L are stressful to most aquatic organisms. DO levels below 1 or 2 mg/L
will not support fish.
If DO is very low it may indicate that there is a lot of organic material that decomposers
are breaking down. Decomposers use up oxygen as they do their work. Also, too much
algae can cause big changes in DO. Algae can make DO high in the day when
photosynthesizing and low at night when the plants are respirating and then become
material for decomposers as the algae dies.
Ammonia
Procedure:
Follow the procedures in the ammonia test kit carefully. WEAR PROTECTIVE
EYEWARE and handle the chemical packets with care. They can cause bodily harm if
not used properly.
Why Measure?
Ammonia is extremely toxic and even in relatively low levels poses a threat to aquatic
organisms. Ammonia is produced by all animals, including humans, as part of normal
metabolism. Most animals immediately convert it to a less harmful substance, usually
urea, and excrete it as urine. It also is released during decomposition of plants and
animals.
Fish shortcut this process and continually excrete metabolic ammonia directly into the
surrounding water via special cells in the gills. In a natural environment it would be
immediately diluted to harmless levels. However, in the confines of aquaria and ecobottles, levels can rapidly rise to dangerous levels unless it is constantly removed. One
way ammonia is removed is with denitrifying bacteria. Denitrifying bacteria break
ammonia down into less harmful nitrites and they live everywhere including natural
bodies of water. You may also choose to dilute the ammonia by removing some water and
replacing it with fresh water.
Communicating What You Have Learned
This lab is designed to give you an opportunity to observe, apply and reflect on content
themes that developed throughout the year. The major themes include:
 Measurement and Science Practices
 System principles (change, inputs/outputs, boundaries/limits, interconnections and
interactions)
 Matter and Energy (conservation, cycles)
 Sustainability
Grading this Lab
Communicate observations/ measurements
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Data table is well designed
Data for each school day is entered and is thorough and makes sense
Data captures what happened in your ecobottle
Analyze and conclude with a scientific explanation
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50 points
50 points
Your analysis should be written in paragraph form and not as separate statements.
It should be well written.
Use the following prompts to help with your analysis.
 Discuss general changes that occurred during the time you observed your ecobottle.
What might explain why the changes occurred?
 Discuss the living organisms that were in your ecosystem. What kinds of things were
there to begin? How did the organisms change? What might explain why the organisms
changed (if they did)?
 Reflect on whether you were able to create a sustainable pond ecosystem. Be able to
explain what sustainable means. What factors contributed to the success or failure?
What would you change if you were to do this over again?
 Write a scientific explanation (claim, evidence, reasoning) that captures the results from
your
 Respond to the following statement: Human population continues to grow while the
planet and the resources from it are finite. What is your perspective about human
sustainability on this planet? How does this relate to the results you got in your ecobottle? What should society focus on to enhance sustainability on this planet?