Classroom Aquaponics: Exploring Nitrogen Cycling in a Closed System


This web resource provides background on the nitrogen cycle and aquaponics, an explanation of the activity, and tips for tailoring the experiment. Nutrient cycling is a fundamental concept in biology. However, many students have trouble visualizing how individual nutrients (e.g.,nitrogen) cycle through complex natural ecosystems. To address this issue, this unit outlines an inquiry-based approach to investigating nutrient cycling in a simplified desktop ecosystem involving aquaria and hydroponically grown plants. Although nitrogen is a particularly important component of the biosphere because it is required in large amounts as an essential component of proteins, nucleic acids and other cellular constituents, students often bring little prior knowledge of nitrogen cycle to biology classes. This inquiry based lab allows students to set up a closed environment to study nitrogen in environments.

Standards & Objectives

Academic standards
CLE 3001.7.4
Apply and adapt the principles of written composition to create coherent media productions.
CLE 3210.3.4
Describe the events which occur during the major biogeochemical cycles.
Alignment of this item to academic standards is based on recommendations from content creators, resource curators, and visitors to this website. It is the responsibility of each educator to verify that the materials are appropriate for your content area, aligned to current academic standards, and will be beneficial to your specific students.
Learning objectives: 

Student will:

  • Learn to identify components of the biotic and abiotic environment
  • Learn to differentiate between heterotrophic and autotrophic organisms
  • Understand nutrient cycling (nitrogen cycling in particular)
  • Measure levels of ammonia, nitrite, and nitrate
  • Measure plant growth
  • Construct graphs of nutrient levels and plant growth rates
  • Generate hypotheses about the impact of nutrients on plant growth 

Lesson Variations

Blooms taxonomy level: 
Differentiation suggestions: 

This lab can be made much more hands-on and open-ended with a few simple steps. First, consider letting the students design the setup. Second, use replicates and adjust the variables. For instance, what happens if you use more plants, less plants, none? What about the number of fish? Do plants grow better in normal hydroponic solution or on the fish effluent? How does photoperiod affect plant growth rate? How does pH change over time in each tank? Does that impact plant growth? Bacterial conversion rates? Fish growth? This project can be easily modified to fit whatever goal you have for your classroom, it is relatively inexpensive, and it incorporates large amounts of potential content and plenty of opportunity for inquiry. 

Helpful Hints

Equipment and Materials:

  • 10-gallon aquarium
  • under-gravel filter
  • small water pump
  • fine/coarse gravel
  • bacterial culture starter solution -- available in all pet shops
  • standard water conditioner -- available at pet supply stores
  • Styrofoam board - or other floating substrate
  • lettuce seedlings in rockwool -- can be grown by students or purchased
  • lights
  • ornamental aquarium fish (~5)
  • aquarium test kits for ammonia, nitrite, and nitrate (~$10/kit x 50-75 tests/kit)