Published by the University of California, Santa Cruz
Scientists from the University of California, Santa Cruz, partnered with Pie Ranch, an educational farm in Pescadero, to study the sustainability payoffs of fertilizing plants with water removed from aquaculture, an age-old practice.
Since October, UC Santa Cruz researchers have filtered water, or “backwash,” out of aerated, recirculating tanks filled with 200 swimming rainbow trout—and then used that water to irrigate native plants at the farm. The team is investigating why the backwash might especially help the plants to grow, building on limited scientific literature on the topic. They plan to share findings next spring. In the meantime, the Amah Mutsun Land Trust, in partnership with Pie Ranch, are using some of the native plants from the study to restore the ranch’s CZU wildfire burn scars.
Stavros Boutris and Anne Kapuscinski feed some of the 200 rainbow trout living in recirculating aquaculture tanks at Pie Ranch during the experiment. Photo: Carolyn Lagattuta
Anne Kapuscinski, an environmental studies professor and the director of the UC Santa Cruz Coastal Science and Policy Program, is leading the research team. She typically focuses on reducing the environmental impact of aquaculture—but now, she wants to do the same for agricultural land, too. On Pie Ranch, a working farm, she hopes to show how intertwining two types of food production can save resources, like water.
“At a farm like this, you could easily grow the fish and grow the crops, and never the twain shall meet,” said Anne Kapuscinski, the lead researcher. “But I think the idea of integrating these systems makes a lot more sense, if you’re trying to build climate resilience.”
The project received funding from the UC Santa Cruz Center for Coastal Climate Resilience (CCCR) and through Kapuscinski’s role as the Robert Headley Chair for Integral Ecology and Environmental Justice.
UC Santa Cruz researchers have often worked with Pie Ranch, a 20-year-old nonprofit, organic farm, which is a short drive away on Highway 1. Pie Ranch co-founders Nancy Vail and Jered Lawson both hold ties with UC Santa Cruz. Lawson earned his undergraduate degree there and Vail ran the university farm.
“It’s almost in my bones now, as far as this potential of bridging academia and research interests with solving real-world challenges,” said Lawson.
Undergraduate research assistant Madison Medina waters native plants with filtered aquaculture backwash water as part of the experiment. Photo: Kapuscinski
The new study fits into ongoing habitat restoration work at Pie Ranch. Some of the experimental plants will go into agricultural fields as hedgerows — or windbreaks — and into riparian habitat along a creek bed that burned in the 2020 CZU Lightning Complex Fire. In that wildfire, invasive eucalyptus trees acted like a wick, and flames razed infrastructure and licked orchards, crop fields and creek beds.
Today, the Amah Mutsun Land Trust — the nonprofit arm of the Amah Mutsun Tribal Band that formed a partnership agreement with Pie Ranch in 2014 — is working to replace the surviving eucalyptus with different native plants. They selected and approved the use of the native plant species for the new study.
“Our ancestors were given the responsibility to take care of mother earth, and that was a really important directive from Creator,” said Chairman Valentin Lopez, who leads the Amah Mutsun Tribal Band and is the board president of the land trust. “And for 20,000 years or more, they learned how to take care of landscapes.”
Chairman Lopez added, “What we’re doing today as a land trust and with our partnerships, like with Pie Ranch, is restoring the path of being scientists and learning about how to take care of mother earth. We’re learning how to do that together.”
The research team took pains to time the life cycles for the experiment, so the plant seedlings were old enough to receive backwash as soon as the fish offered it. There were a couple false starts. But finally, as the rainbows swam and thrived in their blue tanks, seedlings emerged in a nearby greenhouse.
“We kept asking, ‘When are the fish going to be here?’” said Leonard Diggs, who is leading the experiment’s agricultural component. “We spent time setting up the trial, growing the plants and we all had anxious feelings about wanting to match the growth stage of the plants with the availability of the fish effluent.”
Diggs directs Pie Ranch’s Cascade Regenerator Program, which supports emerging farmers from communities historically denied land access. The program also hosts infrastructure that members of the land trust use to cultivate plants.
The experiment involved raising three different native plant species, watering half of the plants with backwash and the other half with plain well water. Over time, the researchers recorded the weight of the whole plants, roots and leaves as well as leaf area. They also measured water use efficiency and conducted in-depth analyses of the soil.
Kapuscinski takes a soil sample from a native plant grown through the experiment. Photo: Carolyn Lagattuta
Researchers evaluate the health and growth of a native plant from the experiment. Photo: Carolyn Lagattuta
“If we do see growth promotion for the native plant species with the fish water, we can at least get a first cut at what might be contributing to that,” Kapuscinski explained. “The results will also point us in the right direction about the role of any change in the soil’s nutrients and biodiversity of microorganisms.”
Some of the plant species the land trust chose are culturally relevant foods or medicines. There’s sensitivity around sharing the medicinal uses to protect against possible extraction or accidental misuse. For example, medicinal uses are not shared through the Amah Mutsun Relearning Program at UC Santa Cruz’s Arboretum and Botanic Garden.
“There’s a whole worldview from an Indigenous perspective that’s missing from contemporary ethnobotany, and it was for those reasons that the Amah Mutsun and Chairman Lopez asked us not to interpret medicinal plants,” explained Rick Flores, a research associate for the Amah Mutsun Land Trust and the steward of the relearning program.
Pie Ranch is such a unique type of farm. So Kapuscinski hopes for her study to comment on both the benefits and some of the barriers other farms might face in adopting similar agriculture-aquaculture systems — and hopes her research will encourage them to add fish production to diversify their income streams.
Kevin Fitzsimmons, an aquaculture specialist based in water-starved Arizona, did not take part in this study but hopes it’s encouraging for farmers.
“Big industrial operations look around for places to dispose of their effluent water and extra manure, which family farms used to just integrate without a thought,” Fitzsimmons said. “Farmers have specialized so much that there’s few going back to this holistic, integrated way of farming.”