Novel experiment at Shelburne Farms works with fungi to curb phosphorus pollution
Researcher Jess Rubin examines a young willow at Shelburne Farms on a recent afternoon.
Photo by Aylin Arifkhan
Riparian buffers are a big deal in Vermont. Millions of state dollars have been spent on planting vegetation between farmland and waterways to help stem fertilizer runoff — and the blue-green algae blooms stimulated by it — by letting the plants remove excess nutrients from soil.
A novel experiment at Shelburne Farms aims to enhance that process along Lake Champlain by using fungi. The ecological restoration project is centered on a relatively new strategy called myco-phytoremediation, a type of bioremediation — using nature to restore nature.
It was born out of a collaboration between the Burlington-based company MycoEvolve and a lab in the University of Vermont’s Department of Plant and Soil Science. MycoEvolve provides nature-based restoration services for degraded and contaminated sites and is spearheaded by founder Jess Rubin.
You could find Rubin one sunny day this spring on a research plot at Shelburne Farms. Past a tunnel of buckthorn so dense it blocked the sun was a streamside clearing where the shrubs had been swapped for fledgling young willows. A mesh fence bordered the clearing, and inside it was Rubin, trimming stray branches and pulling up weeds to give those trees the best chance at thriving.
Clearing all that buckthorn took three campaigns across two years, to make sure the plant’s underground energy reserves were tapped out. But it was worthwhile: Common buckthorn, an invasive species on Vermont’s noxious weed list, has deleterious effects on forest regeneration and wildlife, notably from the laxative effect of its berries.
Along with invasive species, Shelburne Farms struggles to mitigate phosphorus in its soil and waterways, a legacy of using early chemical fertilizers in the mid-20th century. Although the farm does not currently apply fertilizer to its fields, phosphorus is still present in cow manure, which finds its way into streams during rain events and into Lake Champlain.
“That’s why Jess’s site is a good one, because it’s (a point) source that’s traditionally from some of the dairy farm, but a lot of it is from the soil itself,” said Megan Camp, vice president and program director at Shelburne Farms. “If we could prevent all the phosphorus from running into the lake today, which we should still continue to do, there’s still this challenge of legacy phosphorus to deal with.”
The main point source of phosphorus that MycoEvolve is trying to mitigate is a 50-square-yard compost pile upslope of the experiment site. The average level of phosphorus in soils at the site, according to the researchers, is about 17 times the maximum of a healthy range as described by the Environmental Protection Agency.
“We’ve done a number of initiatives to reduce phosphorus runoff,” said Camp. “One is we’re a grass-based dairy farm, so we don’t till the land. So we really greatly reduce runoff by having a perennial like grass in pastures.”
Another mitigation technique employed by the farm is a constructed wetland designed to intercept runoff from the manure pit — which contains high concentrations of phosphorus — before it percolates into a natural wetland and subsequently the lake.
Constructed wetlands are a proven method of water purification, but Rubin’s research shows that restorationists can find better results by incorporating fungi — known as mycorrhizal fungi –– that can form mutually beneficial relationships with plants. While plants have roots, these fungi have hyphae, which are finer and can more nimbly explore soil and mine nutrients that plants can struggle to collect.
In exchange, host plants can feed fungi with carbohydrates produced through photosynthesis. It’s an ancient relationship that dates back 400 million years, when fossil records from Scotland show early terrestrial plants began associating with types of fungi that helped them survive in harsh, infertile soils of the late Paleozoic. Today, up to 80% of all terrestrial plants are adapted to living with mycorrhizal fungi.
“In general, they’re kind of like an ecological scaffolding or a green infrastructure of much of the plant community that we see today,” Rubin said.
In the presence of scarce nutrients, those associations can make the difference between survival and mortality. However, when soils are saturated with nutrients, such as at Shelburne Farms, the relationships can deteriorate, with the fungi no longer providing any more nutrients than the plants can get by themselves but continuing to suck carbon from the plants in a parasitic manner.
This is one explanation for early data from the Shelburne Farms experiment that shows decreased plant vitality in the plots where fungi have been introduced compared to plots where they have not, according to Rubin. Only more data and more replication can show whether that is a definite trend. Currently, there is only one plot with fungi. The other treatment plot only uses buckthorn removal.
Already the experiment has yielded other, promising results: in fungi-inoculated plots, soil phosphorus levels were significantly lower, and the concentration of phosphorus in plant tissue was significantly higher. If implemented at a larger scale, along with cyclical harvesting of the plants, the researchers believe the technique could mitigate some of the phosphorus pollution going into Lake Champlain from Shelburne Farms if maintained over several decades.
The team hopes to triple the size of the experiment to add statistical strength to the findings. When that expansion happens, Rubin said, the researchers will use fungi sourced from a wild area of the farm, rather than the commercial mix used now, and the plants used in the restoration will be revised in collaboration with Vermont Abenaki partners — a social justice angle to the restoration work.
“I’ve grown up with the awareness that we are on unceded territory,” Rubin said, describing her affinity for this type of work and her approach to academia. “One of my kind of secret missions involves bringing in the first peoples and their wisdom as equal participants — if not more appropriately guides and consults.”
MycoEvolve has planted a diverse array of native species, 88% of which are culturally relevant to the Abenaki, such as elderberry, which is used for medicinal syrups, and willow, which is used for baskets.
“When we designed the plant palette originally, it was really through paddles and walks and observations,” Rubin said.
Luca Kolba, MycoEvolve’s research assistant, said the project has dual priorities — to restore the environment within a scientific framework and to give Abenaki greater access to their ancestral lands — and balancing those is challenging.
“We’ve been learning as we go, and it’s really hard holding these goals as we’re still operating within a colonial scientific complex, and we’ve definitely hit some road bumps,” said Kolba, who wrote MycoEvolve’s guide on how to grow native mycelium, the below-ground body of a fungus.
In the next phase of the project, the team wants to bring on Abenaki youth to be part of the harvesting that ultimately removes phosphorus from the soil. The team will also work with a state branch of YouthBuild, a federal youth trades program, and the nonprofit Vermont Youth Conservation Corps in creating the six new plots for the experiment, which, along with fighting phosphorus, could provide more pollinator habitat.
The project dovetails with Shelburne Farms’ community-focused mission. This year the farm launched an educational program with Champlain Valley Union High School to introduce students to fieldwork and applied sustainability as they assist the remediation project. Signs along the Tunnel Trail provide visitors with information about the invisible processes going on beneath the ground that both help and harm the lake ecosystem in tangible ways.
“People will just stumble upon her research while they’re out taking a beautiful stroll on the property and go, huh, I never really thought of that before,” Camp said, referring to Rubin. “We’re definitely not perfect yet, and Jess is helping us become better.”
