Comparing Radish and Wheatgrass growth in Aquaponic Garden

Research Question and Hypothesis: How does the addition of beneficial bacteria to an aquaponic system affect growth rate of plants?

Nitrification in Aquariums - a fishy nitrogen cycle

Plants and animals need nitrogen in its monatomic form to build proteins, among other things, but our atmospheric nitrogen is diatomic, and triple-bonded. It takes either very high heat, a energy intensive chemical reaction (the Haber process), or nitrogen fixing/nitrifying bacteria to break it apart. Typically this bacteria can be found in healthy soil on the roots of legumes.

Another way to get the nitrogen is through animal waste -- but we don't need dirt. As fish poo builds up in an aquarium, bacteria grows that converts some of the waste to Ammonia. Even at low levels, Ammonia is very toxic to fish. As Ammonia levels rise, another bacteria grows that converts Ammonia to Nitrite (nitrosomas). Although Nitrite is not as toxic as Ammonia, it is still harmful to fish. As Nitrite levels rise, another beneficial bacteria (nitrobacter) grows that converts Nitrite to Nitrate. This process is called aquarium cycling or the aquarium nitrogen cycle.

Nitrate is generally non-toxic to fish except at very high levels. Nitrate cannot be removed from freshwater aquariums by the beneficial bacteria, because the bacteria necessary to remove Nitrate grows in an environment deprived of oxygen. There is too much oxygen in freshwater tanks to allow this. Nitrate is removed with regular partial water changes…and that’s why partial aquarium water changes are important.

First Try with the Enzymes and Bacteria

Second Try without the Enzymes and Bacteria

Standards

MS-LS1-6. Construct a scientific explanation based on evidence for the role of photosynthesis in the cycling of matter and flow of energy into and out of organisms. [Clarification Statement: Emphasis is on tracing movement of matter and flow of energy.] [Assessment Boundary: Assessment does not include the biochemical mechanisms of photosynthesis.]

MS-LS1-7. Develop a model to describe how food is rearranged through chemical reactions forming new molecules that support growth and/or release energy as this matter moves through an organism. [Clarification Statement: Emphasis is on describing that molecules are broken apart and put back together and that in this process, energy is released.] [Assessment Boundary: Assessment does not include details of the chemical reactions for photosynthesis or respiration.]

MS-LS2-1. Analyze and interpret data to provide evidence for the effects of resource availability on organisms and populations of organisms in an ecosystem. [Clarification Statement: Emphasis is on cause and effect relationships between resources and growth of individual organisms and the numbers of organisms in ecosystems during periods of abundant and scarce resources.]

MS-LS2-3. Develop a model to describe the cycling of matter and flow of energy among living and nonliving parts of an ecosystem. [Clarification Statement: Emphasis is on describing the conservation of matter and flow of energy into and out of various ecosystems, and on defining the boundaries of the system.] [Assessment Boundary: Assessment does not include the use of chemical reactions to describe the processes.]

MS-LS2-4. Construct an argument supported by empirical evidence that changes to physical or biological components of an ecosystem affect populations. [Clarification Statement: Emphasis is on recognizing patterns in data and making warranted inferences about changes in populations, and on evaluating empirical evidence supporting arguments about changes to ecosystems.]

Experimental Design

For my Study, I used Zymbac, which contains beneficial bacteria in a solution often used to jumpstart aquaponic gardening system. Instructions on my aquaponic system called for a container of it (25mL) to be deposited on the seeds when planting (dropping them on the rocks), and this is what I did for the first group. For the second group, after harvesting the plants, I cleaned the aquariumand the rocks which the seeds grow on, changed the water, and did not add any Zymbac.

Independent and dependents variables

The independent variable in the this case is the added bacteria, and the dependent variables were the rate of

plant growth, and environmental conditions.

Series

This study examined the growth rate of plants (dependent variable) as a function of time (dependent) and the addition of the bacterial solution (independent variable) in the same location (my living room) and at the same environmental (temperature/humidity/light) conditions.

Constants and Controls

There was no control group, only 2 groups of growing plants, one with Zymbac, the other without.

Materials

1. Fish

2. Tank

3. Zymbac

4. Seeds

5. Net Pots

6. Submersible pump

7. Photons

All materials were acquired together in the aquaponic kit, except the fish and the water.

Procedures

For the first trial, I simply followed the instructions included in the kit. I soaked the seeds, went to Petco and redeemed the fish voucher for a fish, assembled the net pots into the tray, filled them with stones, and poured Zymbac on the stones. Finally, I distributed the seeds over theh stones and went out to dinner. I photographed the top of the tank every day, then uploaded the photos into a Picasaweb folder. This allowed me to use Youtube's collage application to illustrate the growth.

The graphs below illustrated nitrification of aquarium water

Analysis & Conclusions

Adding the Zymbac first caused the radish sprouts and wheat grass to grow much faster.

Both radish sprouts and wheat grass, once germinated, grow slowly (1-2mm/day) until they develop (grass) or deploy (radish) their green leaves. At this point their growth is much faster, sometimes more that 2cm/day. Despite my newfound expertise in aquaponics, the 2nd batch of wheatgrass and radish sprouts took longer to arrive at a rapid stage of growth. The instructions on the seed package called for soaking the seeds in room temperature water for 6-8 hours. I soaked mine for seven hours each time.

References

The Aquaponic Garden I bought

Good Bacteria: The Aquarium Water Gold Standard