Our Experiment

Hybrid Aquaponics: Integrating Lunar Regolith and Aquaponics to “Plant the Moon”

  • How does the type of aquaponics water affect plant growth in lunar regolith?

  • How does the ratio of lunar regolith to clay pellets affect plant growth?

Background

Our experiment seeks to explore how principles of aquaponics can be used to grow edible plants in lunar regolith. We know that it is possible to grow plants without soil using agricultural methods such as aquaponics, so we wanted to test if lunar regolith could be used as a growth medium in an aquaponics system. Instead of shipping organic materials to the Moon to turn lunar regolith into Earth-like soil, we would propose integrating lunar regolith and aquaponics to create a sustainable ecosystem for plant growth, protein production, waste disposal, and in-situ resource utilization.

Experimental Design

We set up four aquaponics systems, generously donated to our school by AquaSprouts, each with varied biological activity Tank A uses distilled water as a control. Water from a separate, well-established aquaponics tank was transferred to experimental Tank B to form a decoupled aquaponics system. Tank C has two snails (Pomacea bridgesii) in the tank. To Tank D we added fifty red wiggler worms (Eisenia foetida) to the grow bed media.

Within each aquaponics grow bed, we placed four levels of regolith:pellet ratios in individual moisture-wicking cups. Understanding that the maximum soil amendment is 50%, we will still test a 100% clay pellet level to represent pellets being made from lunar regolith. This will be used for comparison to traditional aquaponics.

Design Matrix

Hypothesis

We think that mixing clay pellets with simulated lunar regolith will increase the growth of plants in the regolith because there will be more air gaps in the soil. We also think that using water with waste from fish, snails, and worms will provide natural fertilization for the plants. We predict the worm water will have the best plant growth because worm castings are rich in nitrogen and commonly used as a fertilizer in gardens.

Independent Variables

Water (Independent Variable #1)

Four different types of water from four different aquaponics systems, increasing in biological activity with each level

  • Tank A: Distilled water (control level for comparison)

  • Tank B: “Fish water” transferred from existing aquaponics system, representing decoupled aquaponics system or treated human wastewater

  • Tank C: “Mystery” snails (Pomacea bridgesii) in the aquarium

  • Tank D: 50 red wiggler worms (Eisenia foetida) in the grow bed

Soil Amendments (Independent Variable #2)

Clay pellets were mixed with lunar regolith in varying amounts (% by volume)

  • 100% lunar regolith

  • 75% regolith : 25% pellets

  • 50% regolith : 50% pellets

  • 100% pellets (control level for comparison)

The 100% pellet level represents a “true” aquaponics system where aggregate clay pellets are used in place of soil. It was included in this experiment for comparison, and it is our proposal that any pellets used on the Moon would be manufactured by in-situ resources and not transported from Earth.

Dependent Variables

By adding more nutrients from the worm, snail, and fish waste, we expect that the plants will be healthier and grow more. Plant growth will be measured and tracked as described in the next section. Our primary dependent variables are plant height and the number of leaves.

Measurements

We monitored plant growth by counting leaves and measuring height (in cm). We also recorded soil and water pH tests and water parameters such as ammonia, nitrite, nitrate, and hardness. We counted the leaves and measured the height of each plant several times a week, keeping a chart for each tank.

Controls

We kept the type of lights the same, the volume of water, the total volume of moon soil and/or pellets, the water pump timer, water heater temperature, the height of the grow lights, and the time we left the lights on (12 hours). We used the same type of plant for each pot. We chose watercress because it has high nutrient content, grows well in moist soil conditions, and tolerates high pH.

Results

Some of the plants did not survive, but in Tank D that had worms, the 100% pellets cup had plants that grew very tall and strong. These were our best plants, measured by plant height and number of leaves. We also had good growth in the decoupled fish tank, which was Tank B. In general, adding clay pellets to the lunar regolith resulted in better plant growth.

Figure 1 shows how the number of leaves was affected by the amount of clay pellets that we added to the regolith. We learned that as you add more pellets to the regolith the more variability you have in the number of leaves, so we would recommend you use a 50:50 mix of both as it is more consistent with the increased amount of leaves.

Figure 2 shows that different kinds of tank water affected the number of leaves. We learned that the worms in the aquaponic systems produced the greatest results on average, but the plants had the most variability. The decoupled fish and the snails had similar results. The distilled water produced the worst results. If only one species could travel to the Moon, we would suggest taking red wigglers. Eventually, all three species would be good to have in aquaponics on the Moon, because greater biodiversity leads to a healthier ecosystem.

Figure 3 shows how different mixtures of regolith and pellets affected the height of the plants. We discovered that the 100% pellets had the best height although it is inconsistent for different water types. We would recommend a good blend of pellets and regolith since it produced the most consistent results throughout our experiments. As with leaf count data, we had no measurable plant height in the 100% lunar regolith.

Figure 4 shows how the different kinds of tank water affected the heights of our plants. We learned that the worm water yielded the best results, although it had the most variability. We would recommend further research into using snails and/or fish along with worms to get the best plant height. The distilled water showed the worst results when it came to plant height. This was to be expected.

Discussion & Conclusions

We were able to grow watercress in lunar regolith by mixing in 25% to 50% clay pellets (by volume) in moisture-wicking pots that were set in an aquaponics grow bed. As hypothesized, the pellets helped make the lunar regolith better for plant growth. Our second hypothesis was also supported because we found that wastewater from fish, snails, and worms contributes to better plant growth when compared to distilled water. This is promising research because future lunar explorers can incorporate what is known about aquaponics to make use of the abundance of available lunar regolith. We do not need to ship organic material to the Moon to make the soil viable; we can use Moon soil to establish an aquaponics ecosystem with an initial colony of worms, snails, and/or fish. This is a natural, efficient, and sustainable method of growing plants that can also provide protein for future lunar pioneers.


More experiments are needed to determine the best plant type for this arrangement. We found that moisture-wicking pots are highly efficient in soaking up water; the soil remained constantly saturated but densely packed. We selected watercress as our plant, based on its tolerance to higher pH and moisture; however, we discovered that the roots were too fragile and not strong enough to push through the soil. Aquaponics with moisture-wicking pots would work well on the Moon, but a different type of plant might be a better option. We look forward to investigating this aspect further in our next project.