Nitrification in a Balanced Nitrogen Cycle Workshop

In this workshop high school students learn the importance of nitrification in an ecosystem with the nitrogen cycle in equilibrium. The workshop is appropriate for students who might not yet have had a course in biology or chemistry. The workshop can work with a group of 10 to 20 students.

Project overview

The students work in groups to establish four aquarium-contained ecosystems, two illustrating an ecosystem going awry and two illustrating the establishment of an ecosystem in equilibrium. The aquariums contain water from different sources (lake, rain, or tap water), and any combination of soil, aquatic plants, and fish. The students test the effects of light and temperature cycles, agitation, aeration, addition of nutrients and metals.

The students monitor with readily available test kits, the pH, oxygen, ammonia, nitrite and nitrate content. The students record in the span of ten weeks the changes occurring in the aquariums. It is recommended that one session be dedicated to instruct the students how to design an experiment.

Number of sessions

The workshop takes place over approximately 10weeks: one lecture in which the students get an introductory lecture, design and start the aquariums; one weekly session to asses the state of the aquariums and to take samples as appropriate; three sessions for preparation for a presentation, presentation and discussion of findings.

Inquiry-based learning objectives

a) familiarization with the nitrogen cycle,
b) formation of a testable hypothesis,
c) drawing conclusions from the different treatments and outcomes.

Information resources

Students are encouraged to search for aquarium test kits locally or by using the Internet. URL links are given for background information including the nitrogen cycle and its importance in balanced ecosystems and for the most up-to-date research in nitrification.


Students gain an understanding of the components necessary for the establishment of a nitrogen-balanced ecosystem (i.e. a complete nitrogen cycle). Students learn to design an experiment, to predict the outcome and to keep records of their observations. Students learn that in an ecosystem the pH and concentrations of ammonia, nitrite and nitrate affect its viability. The students present their findings to their peers and receive constructive feedback from all participants. Students practice communication skills in conveying the results of their experiments to their peers.

Suggested schedule for the workshop

In the initial session, students plan the composition, location and variables to be tested for each aquarium. Students also learn how to test for ammonia, nitrite, nitrate and pH changes. In addition, dissolved oxygen in the water can be tested if an adequate instrument is available. Similarly, microscope observations may be performed to record the microorganism numbers, diversity and characteristics (i.e. motile, elongated, ciliated, etc).

The aquariums are tested weekly for at least 10 weeks. The aquariums should be tested one last time on the 10th week and conclusions drawn. Photos may be taken at this time.
Finally, students prepare a 5- to 10-minute presentation with visual aids.

Protocols and materials:

Aquariums of 10 to 12 gallons are recommended. Aquarium air pumps and heaters are necessary if fish are considered. Mixing water from different sources may be included, such as tap water with pond, city, lake, or river water, etc.

Kits for ammonia, nitrite and nitrate content determinations are readily available at pet stores dealing with aquariums, or students can search the Internet for suppliers of test kits.

Suggestions for aquarium variations

Students can vary conditions of aeration, stirring, light or any combination thereof. Variations in the components of the aquarium can be also be tested (e.g. aquatic plants, pond water, tap water, lake water, garden soil, minerals, etc).

Include fish only in those aquariums that are considered viable.

Suggested question for discussion: What are the requirements for an ecosystem in equilibrium?

Data collection

At one-week intervals the aquariums are tested. Following the instruction in the kits, measurements for ammonia, nitrite, nitrate, contents and pH in the aquariums are recorded. Perform a visual observation and use a microscope if available.

This workshop has contributions from D. Arp, K. Halsey and L. Sayavedra-Soto from Oregon State University, USA