Effects of Nitrogen, Oxygen and pH
on Ecosystems
Engage
Do you recognize this symbol?
Why is it a continuous loop?
You might be surprised to learn that the process of recycling is not just a human
endeavor. Everything in nature is recycled…from the air we breathe to the water we
drink. In fact, the amount of matter on Earth today is essentially the same amount of
that existed on Earth a millions of years ago.
Through biological and geologic processes, this matter is not destroyed, but it is
changed from one form to another (Law of Conservation of Matter). Ultimately, the
changes convert the matter back to its original form. Imagine a world where materials
were not recycled: once something was made it would never change. Many necessary
materials would be used only once, and future generations would never be able to use
them.
Fortunately, this is not the case. As you know, plants and animals decompose, freeing
up nutrients such as carbon, nitrogen, phosphor, sulfur, oxygen, etc., to be used for
other processes. Also, humans ingest food and excrete waste. Our waste, however, is
food for other organisms. They excrete waste, which, in turn provides food for other
organisms. Finally, the products are the plants and animals that humans eat. Thus the
cycle repeats. To function, these cycles require many different organisms as well as
different abiotic mechanisms.
What happens if one step of a cycle is missing?
How do different organism rely on each other to complete these cycles?
What would happen if there were no decomposing bacteria in our ecosystems?
Explore
In this activity, your group of three will explore whether or not organisms can flourish
without other organisms. Each person in your group will set up ONE type of aquarium:
a fish tank, a bacteria tank or a plant tank. You will take daily measurements of
ammonia, nitrate, nitrite, and dissolved oxygen to monitor the health of each type of
organism in the individual tanks. Think about the inputs and outputs of your aquarium
and what is missing.
Materials:
Each person will need:
1-gallon aquarium
¾ gallon of springwater or conditioned tap water
Ammonia test strips
nitrite/nitrate test strips or titration kit
DO Titration kit or DO tablets
pH strips
For the bacteria tank:
Aquarium pebbles
Start Zyme bacteria starter
For the fish tank:
5-10 fish
fish food
For the plant tank:
Foam plant quad
cotton ball
8 Radish seeds
Bacteria Tank Set-up:
1. In your lab notebook, predict what will happen to the bacteria over the next
several days. What will happen to the ammonia, nitrate, nitrite and dissolved
oxygen levels?
2. Set up a 1-gallon aquarium with ¾ of a gallon of spring water or conditioned tap
water at your workstation.
3. Add enough aquarium pebbles to cover the bottom of the aquarium.
4. Pour one capful of Start Zyme into the tank. Start Zyme contains bacteria that
convert ammonia.
5. You will be recording data every day for 1.5 weeks. M-W-F you will measure
ammonia, nitrate, nitrite and temperature. On Tuesdays and Thursdays, you will
be recording D.O and pH. Create a data table to include dates for those
measurements.
6. Following the directions on the bottles, measure the amount of ammonia, nitrate,
and nitrite levels in your aquarium. Record results.
7. Following the directions on the titration kit or dissolved oxygen or dissolved
oxygen tablets, measure and record results. Dissolved oxygen will be recorded
on Tuesdays and Thursdays.
8. Record the temperature of your aquarium each day.
9. Record daily qualitative data that you notice is happening in your aquarium.
10. If any water is added, record this as well. Remember it needs to be spring water
or conditioned tap water.
Fish Tank Set-up:
1. In your lab notebook, predict what will happen to the bacteria over the next
several days. What will happen to the ammonia, nitrate, nitrite and dissolved
oxygen levels?
2. Set up a 1-gallon aquarium with ¾ of a gallon of spring water or conditioned tap
water at your workstation.
3. Add 5-10 fish to your aquarium.
4. You will be recording data every day for 1.5 weeks. M-W-F you will measure
ammonia, nitrate, nitrite and temperature. On Tuesdays and Thursdays, you will
be recording D.O and pH. Create a data table to include dates for those
measurements.
5. Following the directions on the bottles, measure the amount of ammonia, nitrate,
and nitrite levels in your aquarium. Record results.
6. Following the directions on the titration kit for dissolved oxygen or dissolved
oxygen tablets, measure and record results. Dissolved oxygen will be recorded
on Tuesdays and Thursdays.
7. Record the temperature of your aquarium water each day.
8. Feed the fish a very amount of food every other day. Two to three discs is
plenty.
9. Record daily qualitative data that you notice is happening in your aquarium.
10. If any water is added, record this as well. Remember it needs to be spring water
or conditioned tap water.
Plant Tank Set-up:
1. In your lab notebook, predict what will happen to the bacteria over the next
several days. What will happen to the ammonia, nitrate, nitrite and dissolved
oxygen levels?
2. Set up a 1-gallon aquarium with ¾ of a gallon of spring water or conditioned tap
water at your workstation.
3. Pull four small pieces of cotton from the cotton ball and place them at the bottom
of each chamber of the foam quad. There be just enough cotton to cover the
hole.
4. Place two radish seeds into each chamber of the quad.
5. Place the quad into your aquarium so it floats. Push the quad into the water
slightly until the cotton in each chamber is wet.
6. You will be recording data every day for 1.5 weeks. M-W-F you will measure
ammonia, nitrate, nitrite and temperature. On Tuesdays and Thursdays, you will
be recording D.O and pH. Create a data table to include dates for those
measurements.
7. Following the directions on the bottles, measure the amount of ammonia, nitrate,
and nitrite levels in your aquarium. Record results.
8. Following the directions on the titration kit for dissolved oxygen or dissolved
oxygen tablets, measure and record results. Dissolved oxygen will be recorded
on Tuesdays and Thursdays.
9. Record the temperature of your aquarium water each day.
10. Record daily qualitative data (noticeable changes to the water and the seeds)
that you notice is happening in your aquarium.
11. If any water is added, record this as well. Remember it needs to be spring water
or conditioned tap water.
Explain
It is time to research an explanation of the nitrogen cycle. Biogeochemical cycles
are complex processes in which inorganic molecules are cycled through an ecosystem.
The cycle involves geologic as well as biological processes. Many of the common
molecules important to life go through this process, including water, nitrogen,
phosphorus, calcium, potassium, magnesium and sulfur.
In your lab notebook, your job is to further explain the nitrogen cycle, both in a sketch
and in descriptive writing. The terms that you must be familiar with are: aerobic,
ammonia, ammonification, anaerobic, assimilation, cyanobacteria, denitrification,
eutrophication, fixation, nitrate, nitrification, nitrite, & symbiosis as each applies to the
nitrogen cycle. Be sure that you understand the processes that convert nitrogen in one
form to nitrogen in another form, including the chemical formulas for each form of
nitrogen. Also include how any process in the nitrogen cycle might affect dissolved
oxygen levels or pH. Remember to focus on both aquatic and terrestrial processes and
how they affect each of the ecosystems (positively and negatively).
Questions to address:
1. What was missing in your tank from the EXPLORE section to prevent the
nitrogen cycle from functioning? What was the result? (use your data to support
your answer)
2. Discuss with your group members their results and what they were missing from
their tanks based on their data.
3. What would happen to each tank without the nitrogen cycle and why?
4. What were the dominant forms of nitrogen in the fish tank? Where did that come
from?
5. Could your tank subsist as a closed system? Explain your answer.
6. What happens to pH levels as ammonia is converted to nitrate?
7. Besides ammonia, what else needs to be present for the nitrification process to
work?
8. What is the relationship between dissolved oxygen and temperature in aquatic
ecosystems?
9. How are the processes that you explained in your research of the nitrogen cycle
involved in your aquarium?
10. Humans have altered the influx of nitrogen at different stages of the nitrogen
cycle. Pick one way in which this happens and explain what the long-term effects
may be on the environment.
11. How are the measurements you made in your individual ecosystem likely to
affect the success of it for a long period of time?
12. Discuss any trends you see in the data for your individual tank. Why might levels
have been high/low? What could have changed those levels?
13. Compare YOUR results with the other people in your group. Summarize their
results and your discussion.
Extend
With your group, you will now build a functioning system where the nitrogen levels
throughout are maintained allowing the nitrogen cycle to be fully functional and
maintaining dissolved oxygen levels to allow all of the organisms to thrive.
1. Discuss with your group what was missing from each of the different tanks during
the previous investigation.
2. Your group of three is to plan a design with your aquariums prior to building it.
3. Your design must be sketched and explained as to why the set-up is planned in
that way. The three aquariums should be interacting.
4. Once your plan is approved, you may begin building your set-up.
5. Label each tank with the inputs from the preceding tank and the outputs from the
tank that follows.
6. Monitor and record ammonia, nitrate, nitrite, dissolved oxygen, temperature and
pH levels as you did before, but over the course of two weeks.
7. The final product for THIS portion (EXTEND) is a lab report (see template).
8. Even if your system doesn’t work, you should be able to describe the experience,
present relevant data, reach a logical conclusion explaining your results, and
offer insights into what was learned and how the model might be improved. You
will have up to two days to go through the planning and building stages of the
project. After it is set up, you will continue to take measurements for ammonia,
nitrite, nitrate, DO, temperature and pH. This will continue for 2 more weeks.
You will continue to take measurements as you did before.
Additional materials that will be available to you include:
A water pump
plastic trays
tubing
flat and/or angled blocks