By Audra Koscik
Illustration by Audra Koscik
On Earth Day, many gathered in D.C. Smith Greenhouse to celebrate. Attendees munched on vegetarian snacks as they toured each room. The humid greenhouse air was buzzing with energy.
The greenhouse is home to a variety of plants from cacti to corn. Instructors from the College of Agricultural and Life Sciences (CALS) use the space for educational purposes. As a result, the greenhouse hosts many innovative projects such as using hydroponics to grow cucumbers and tomatoes. Attendees toured this educational work with students available to answer questions. The main attraction, however, was the new aquaponics system.
Recently, scientists at the University of Wisconsin—Madison have been exploring the uses and benefits of aquaponics. Aquaponics uses water from fish tanks to fertilize plants. The plants, in turn, filter the water for the fish tank. This cycle supports significantly more sustainable water usage than traditional farming methods.
Aquaponics also has a more sustainable nitrogen cycle. Johanna Oosterwyk, a teaching, learning, and tech manager in plant and agroecosystem sciences, oversees D.C. Smith Greenhouse. Oosterwyk explains, “The nitrogen that we use in conventional fertilizers is fixed by what’s called the Haber-Bosch process. It requires high temperatures and high pressure, and both of those take a lot of energy.” On the other hand, aquaponics introduces nitrogen to the system through fish food. “It’s not being transformed from atmospheric nitrogen into nitrate, which is the fertilizer, and that reduces the fossil fuel cost,” Oosterwyk says.
The sustainable aspects of aquaponics caught the interest of UW—Madison’s Engineers for a Sustainable World (ESW). ESW is a student organization on campus that brings sustainability-related projects to campus and to the community.
Creating more sustainable infrastructure is an important aspect of ESW. Veronica Morse, a civil engineering student and ESW member, says, “A lot of people’s daily actions they don’t have control over. There’s a lot engineering can do to help people.”
Aquaponics was already a practice ESW had experience with. The student group decided to expand their aquaponics work. “Aquaponics is very rewarding,” Morse says. “[Aquaponics] wasn’t really explored on other college campuses, so there’s an opportunity to start the trend.”
ESW worked with the Green Fund, a group within the Office of Sustainability that supports student-initiated projects that implement sustainable infrastructure for campus facilities. The Green Fund awarded ESW over $9000 to build an aquaponics system in D.C. Smith Greenhouse.
ESW students set up the system on Mondays for about 10 weeks straight. The project provided engineering challenges. Owen Knych, an environmental engineering student and ESW member, says, “Since it’s a fish tank and inside there’s no wind or waves like a lake, you need to add oxygen.” The system also had to have the fish visible and all of the plants easily accessible. Additionally, the system had to always connect the roots to the water which provided a design challenge, Knych explains.
Once the system was complete, ESW members volunteered at several events to share the aquaponics system. One of those events was through Earth Fest, hosted by the Nelson Institute for Environmental Studies and the Office of Sustainability.
At this event, visitors experienced hands-on science. ESW students led a workshop where attendees made their own hydroponic planters out of painted jars. ESW students also guided visitors through their aquaponics system.
Attendees also saw an additional aquaponics system. Dylan Mahant, a data science student, works with the Ellison Lab in CALS. The Ellison Lab specializes in alternative crops, such as hemp. Through the lab, Mahant created an aquaponics system in D.C. Smith Greenhouse to research the interaction between aquaponics and low-THC cannabis, also known as hemp.
Mahant’s project focuses on microbes, a key part of aquaponics. Microbes convert the nitrogen in fish waste into a fertilizer the plants can use.
“Every plant needs the big three, NPK,” Mahant explains, referring to nitrogen, phosphorus, and potassium. “The big thing with cannabis is that it needs a lot of nitrogen in its vegetative state, but when it switches to flowering it needs more potassium and phosphorus,” Mahant says. Cannabis’s hefty nutrient requirements make it a good candidate to test with aquaponics.
The Ellison Lab and ESW’s systems use tilapia fish. For future work, Mahant is interested in seeing aquaponics systems with more species. “Different organisms break down food in different ways, potentially making some nutrients more available to the plants,” Mahant says. For instance, snails eat algae, meaning they can clean the tank and add nutrients to the system. Different crops could also contribute to the system, Mahant says.
Ooosterwyk also has expressed interest in adding species to the aquaponics system. “We could use the food that we produce, and any food waste could potentially be fed to insect decomposers,” Oosterwyk says. These insect decomposers could then be fed to the fish, which could help close the loop, Oosterwyk explains.
ESW is expanding their aquaponics work. They are creating an aquaponics system and related educational resources in Spring Harbor Middle School.
D.C. Smith Greenhouse plans to work with ESW in the near future to continue to implement more sustainable infrastructure such as collecting rainwater to use for evaporative cooling.