LESSON EXPLORING AQUAPONICS

Transcription

1 EXPLORING AQUAPONICS TIP: For emphasis on human impact, show the video The Story of Stuff to emphasize the linearity of the material economy today and then contrast it with aquaponics. DESCRIPTION: Students become experts in a particular topic regarding an aquaponics system and collaborate to figure out how the system works. Students measure plant growth, nitrate, nitrite, ph, and ammonia levels for a few weeks and interpret the data as a graph. BACKGROUND INFORMATION: Aquaponics is the combination of aquaculture (fish farming) and hydroponics (growing plants in media other than soil). While commercial aquaponics is a multi-million dollar per year industry, the basic principles and equipment remain easily transferable to the classroom. The central problem in traditional aquaculture is water quality. Raising commercial fish at high density leads to quickly escalating levels of ammonia and nitrite in the water. These compounds are produced naturally in the fish effluent and must be laboriously removed through complex filtration systems in commercial setups, which use valuable energy resources. An analogous situation occurs in your own fish tank at home. Fish produce large volumes of nitrogenous wastes that must be removed by appropriate filters or frequent water changes. Conversely, hydroponic technologies strive to provide plants with a nitrogen-rich source of growing media and a perfect balance of other macro- and micro-nutrients. In this case, the difficulty is simply the high cost of constantly adding soluble nutrients to hydroponic setups. Aquaponics offers a solution to both industries by combining a recirculating system that incorporates three main components: fish, plants, and bacteria. The fish provide ammonia-rich effluent that bacteria quickly convert to nitrite and nitrate. While ammonia (NH4) and nitrite (NO2) are toxic to fish at very low levels (several parts per million, or ppm ), the fish are able to tolerate several hundred ppm of nitrate (NO3). The plants benefit from the nitrogen and nutrient-rich effluent and remove large amounts of nitrogenous wastes (in the form of nitrates) from the water, which is then returned to the fish tanks. The growth of all organisms depends on the availability of mineral nutrients in the environment. 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. Nitrogen is abundant in the earth s atmosphere in the form of N2 gas. However, in this form, nitrogen is unavailable for use by most organisms because there is a triple bond between the two nitrogen atoms that makes the molecule almost inert. Nitrogen can be used for growth if it is first fixed (combined) in the form of ammonium (NH4) or nitrate (NO3) ions. Weathering of rocks releases small amounts of these ions but the process occurs so slowly that it has a negligible effect on the availability of fixed nitrogen. Thus, most available nitrogen is derived from other fixation pathways.

2 PAGE 02 The Nitrogen Cycle: Atmospheric nitrogen can be fixed into biologically available forms, such as ammonia and nitrate, by 1) symbiotic bacteria commonly associated with legumes and with other plants having root nodules, 2) free-living aerobic bacteria, and 3) blue-green algae. Through biochemical pathways, these bacteria break the triple-bonded N2 molecule into two nitrogen atoms, which then combine with hydrogen to form ammonia (NH3). In this way, biological fixation generates approximately 90% of the fixed nitrogen contributed to the biotic environment each year. OBJECTIVES: Students learn that matter (atoms) is not created nor destroyed but cycled around. Nitrogen and Carbon Cycles (Photosynthesis and Respiration, and Nitrification) are examples of this. Students learn how systems thrive off the sum of its parts. COMMON CORE STANDARDS: CCSS: 8.RST 7: Integrate quantitative or technical information expressed in words in a text with a version of that information expressed visually (e.g. graph, model, table). 8.W 1: Write arguments to support claims with clear reasons and relevant evidence 8.W 4: Produce clear and coherent writing 8.SL 1: Engage effectively in a range of collaborative discussions with diverse partners NGSCS: LS2.A: Organisms and POPs are dependent on their environmental interactions with biotic and abiotic things. LS2.B: Atoms are recycled between living and non-living parts of ecosystem LS2.B: Food Webs model matter and energy transfer LS2.C: Ecosystem characteristics vary over time PS1.B: Reactions rearrange different molecules, but number of atoms are conserved PS3.D: Mechanical efficiency can be increased by reducing friction NGSCS Cross-Cutting Concepts: 1. Patterns: Macroscopic patterns are related to the nature of microscopic and atomic-level structure. 1. Patterns: Graphs and charts can be used to identify patterns in data 3. Scale, Proportion, and Quantity: Time, space, and energy phenomena can be observed at various scales using models to study systems that are too large or too small. 3. Scale, Proportion, and Quantity: The observed function of natural and designed systems may change with scale. 4. Systems and System Models: Systems may interact with other systems; they may have subsystems and be part of larger complex systems 4. Systems and System Models: Models can be used to represent systems and their interactionssuch as inputs, processes and outputs- and energy, matter, and information flows within systems 5. Energy and Matter: Energy drives the cycling of matter within and between systems 5. Energy and Matter: Energy cannot be created or destroyed

3 PAGE 03 TIME: 50 MINUTES. THINK-PAIR-SHARE (5 MINUTES); 10 MINUTES PER STATION (3 STATIONS); 15 MINUTE DISCUSSION MATERIALS: Materials for preparation: Back to the Roots Aqua Farm Aquaponics Grow System ($60 Costco), link below: product html or DIY aquaponics system Aquarium test kits for ammonia, nitrite, and nitrate (about $10/kit x tests/kit) One Beta fish (about $5) Materials for activity: 1 worksheet packet per student (includes Stations A-C) PREP: Set up the aquaponics system 2 weeks in advance or more and begin measuring the different variables as the system sets up (ph, nitrate, nitrites, ammonia, plant height) A day or two before the activity, assign students a small research project to learn more about a particular part of the aquaponics system (Fish, Plant, Bacteria) Prepare one Station A per group Prepare one Station B Prepare one Station C per group ACTIVITY: 1. Start with the video on aquaponics: ag.arizona.edu/azaqua/aquaculture_images/ aquaponics/aquaponics_edit_8-fix.wmv 2. Explain to the class how you set up the aquaponics system a few weeks ago and started measuring some components that the students will be continuing soon. Ask students to fill in the information you have. 3. Arrange students in groups of 4 and assign them to Station A, B, or C. Spend 10 minutes at each station. 4. For Station B, assign each group a measurement to measure and record once a week. Two groups can do a measurement if necessary. 5. Write on the board the following table: VARIABLE WEEK #1 WEEK #2 WEEK #3 WEEK #4 WEEK #5 PH # # AMMONIA # # NITRATE # # NITRITE # # PLANT HEIGHT (CM) # #

4 PAGE Wherever there is a # fill in the value for the students. They will be measuring the rest. 7. Have students fill in their average measurement for each item. 8. Feed fish regularly. 9. Measure plant and water quality (ammonia, nitrite, nitrate) variables at regular intervals for 1-2 weeks. 10. Plot the data and discuss the shift in ammonia, nitrite, and nitrate levels in the context of the nitrogen cycle. DISCUSSION: 1. What effect will removing the bacteria have on the aquaponics ecosystem? 2. How is this closed loop system similar or different to how cellular respiration and photosynthesis work together? 3. What effect will increasing the flow of water in the system have on the aquaponics ecosystem? TEACHER TIPS: Instead of purchasing this aquaponics system, you can use found and upcycled items the items to make a DIY aquaponics system. 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, or 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. Have students design a new system for aquaponics using local materials ( appropriate technology ) of a country of choice. They can then display their self-built aquaponics system at a gallery exhibit for parents and locals to whom they can explain how their system works and how their materials are used. For more information on appropriate technology, see the link below: REFERENCES: Mullen, Sean. Classroom Aquaponics: Exploring Nitrogen Cycling in a Closed System: Teacher s Guide. Cornell Science Inquiry Partnerships Web. 21 Oct <

5 PAGE 05 STATION WORKSHEETS/INSTRUCTIONS STATION A Open-Ended Investigation Examine the aquaponics system and bacteria slide on the table. Using only these objects and your homework research, investigate to learn as much as you can about: 1. What does a fish require as input and what can a fish provide as a function or a product?) 2. What does a plant needs as input and what can a plant provide as a function or a product? 3. What do these bacteria need as input and what can they provide as a function or product? STATION B Structured Activity Learn to measure the variables! 1. Your teacher set up the aquaponics system at least 2 weeks in advance. Enter the information on your data table so far. Now measure the variable that the teacher assigned your group. You will be responsible for this variable for the next 3-5 weeks. VARIABLE WEEK #1 WEEK #2 WEEK #3 WEEK #4 WEEK #5 PH # # AMMONIA # # NITRATE # # NITRITE # # PLANT HEIGHT (CM) # # 2. Once you measure your assigned variable, practice measuring the other variables without recording them.

6 PAGE 06 STATION C Identifying and Reading 1. What are all the living organisms in the system? 2. What are all the nonliving parts or habitats of the system? 3. What are the external elements that affect it? 4. Can you think of other ecosystems close to your school? Further Reading: A species of organism is the term used to describe organisms that are closely related. There are different species of fish like tilapia, trout, and catfish. A population includes all the members of a single species that live in a given habitat. A community is a group of different organisms living together in a habitat, for example, fungi and bacteria living in the same pond. The function or position of an organism or population within an ecological community is called a niche. The boundaries of an ecosystem are relative. You could have an entire ecosystem underneath a big rock or you could be talking about the overall ecosystem of the planet (the biosphere). An ecosystem can be as small as an aquaponics system in your classroom or as large as the ocean. That ecosystem includes every living (biotic) and non-living thing (abiotic) in the area such as temperature, wind patterns, sunlight, soil, atmosphere, and precipitation, to name a few.

7 PAGE 07 DIY AQUAPONIC SET-UP The initial setups can be constructed in advance by the teacher or can be incorporated as part of the lab to add a hands-on element and engage students who learn well in active situations. The steps regarding aquarium setup are standard. Any healthy aquarium needs to be set up for at least a few days to a week to be conditioned for fish. In addition, this will help give the bacteria time to become established in the gravel bed. However, these steps can be done by the students with the caveat that data collection be postponed for several days to a week. 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 Upcycled styrofoam board or floating baskets for floating substrate Lettuce/greens seedlings in rockwool -- can be grown by students or purchased lights ornamental aquarium fish (about $5) aquarium test kits for ammonia, nitrite, and nitrate (~$10/kit x tests/kit) INSTRUCTIONS: 1. Set up aquarium with 10 gallons of water at least a week before the lab is planned. (Use rainwater or use an air pump and stone to remove chlorine.) 2. Place under-gravel filter in bottom of tank and cover with 5-10 lbs of gravel. 3. Add approximately 1ml of bacterial culture starter (the farther in advance of the lab this is done the better). The bacteria need several days to become established. Any normal fish tank will have a healthy stock of bacteria in the gravel bed if it has been set up for any significant length of time. (In this case, you do not need the starter culture.) 4. Add the fish to the pre-conditioned tank. 5. Place the water pump in the tank to circulate water and plug in. Cut small (~1 in) round holes in the floating substrate for the lettuce seedlings. Place the rockwool seedlings in the floating substrate and float it on the top of the aquarium. Don't use too many plants, or crowding will affect their growth. 6. Put the plants in the sun while keeping shade on the fish tank (or else algae will grow). 7. Take initial measurements of the plants (height, length, number of leaves, etc.). 8. Take initial water samples and test for ammonia, nitrite, and nitrate.