Ongoing Research Aims to Improve Water Quality, Pollinator Habitat, and Support Abenaki

Aug. 25th 2022
Restored inoculated plot in the field study at the end of the summer

Phosphorus is a nonrenewable nutrient in nature that is essential to all life. Current farming practices use phosphate derived from phosphorus rock in commercial fertilizers and manure to maintain high crop yields. Increased fertilizer use, excessive impervious (paved) surfaces, and depleted soils compound to increase non-point source pollution, which includes stormwater runoff carrying dissolved phosphorus or phosphorus in eroding sediments into waterways. Once there, harmful algae and bacteria can proliferate to cause eutrophication—lowering oxygen levels and threatening aquatic organisms.

A study conducted by Jessica Rubin and Josef Görres of the University of Vermont investigates practices to improve water quality functions of riparian buffers, increase pollinator habitat, and support Abenaki rematriation (return of land to Original Peoples). Riparian buffers separate developed or agricultural land from nearby waterways with vegetation to slow down incoming water and intercept pollutants such as phosphorus or pesticides. They are best management practices in Vermont for landowners. Rubin and Görres suggest that these practices may not be optimal when buffers are degraded; their research focuses on increasing riparian buffer efficiency both for phosphorus removal before it gets to waterways and for improved pollinator habitat along these areas by using mycorrhizal fungi and native plant polycultures in buffer restoration. Mycorrhizae fungi are specialized in connecting plant roots and soils.

In a literature survey, Rubin and Görres highlighted how mycorrhizal fungi can enhance phosphorus uptake by plants, thus removing phosphorus from soil and water when the plants are cyclically harvested. Mycorrhizae are fungi that have symbiotic relationships with plants in and around their roots. The researchers note that 80% of terrestrial plants host mycorrhizae which can facilitate increased phosphorus uptake and thus be harnessed to facilitate removal of phosphorus from soil and water. Their findings led them to conduct their own field and mesocosm studies to determine the role of mycorrhizal plant relationships in riparian buffers.

Field Experiment

The field experiment explores the phosphorus uptake capacity of different plants and associated mycorrhizae that could revitalize degraded riparian buffers on a farm, improve water quality function and increase pollinator habitat. Their restoration team established three research plots along a drainage way at Shelburne Farms in the Lake Champlain basin. One plot, dominated by nonnative buckthorn (Rhamnus cathartica), was left untouched and served as a control. The other two plots were restored with native polyculture (multiple species) vegetation, one of which was inoculated with mycorrhizae. To establish the experimentation plots, their team removed the buckthorn mechanically rather than chemically thereby avoiding use of any herbicides. This accessible, affordable, and efficient method was 90% successful in eliminating buckthorn from the plots.

Their work goes beyond the science. The researchers learned from Abenaki People that many of the native plants in their plant palette are valuable to their traditions and culture. The researchers understood the natural and cultural history of the Lake Champlain basin before colonial times as the framework for their study. While it is now recognized by researchers that there are social and cultural benefits to acknowledging and collaborating with indigenous cultures, Rubin and Görres suggest that it is also necessary in experimental design. Their study begins to consider Indigenous Knowledge as an integral part of their experimental process. This orientation is a small step towards mending the relationship between Indigenous People and science.

“Eighty-eight percent of plants in our palette are recognized by the Abenaki as traditionally used for food, medicine, art, or ceremonial purposes” says Rubin, “We aim not only to restore ecological functions to a landscape damaged from conventional agriculture but also to begin to reconcile social injustices inflicted since the colonists’ arrival.”

The researchers measure the density of mycorrhizae in the soil and in the roots to determine their presence over time in each plot as succession occurs. The restored plot with mycorrhizae did demonstrate decreased levels of soil water and total phosphorus. This suggests that restoring degraded buffers with native plants inoculated with mycorrhizae may benefit the ecosystem by protecting water quality if plants are cyclically harvested.

This field study found mycorrhizae reduced Soluble Reactive Phosphorus (SRP) in the soil which means less phosphorus is available to reach waterways. In the restoration plots, almost two times more species grew than were planted and the restored plots had four times more pollinator species than the control buckthorn plots which shows that restoring the plots is ecologically beneficial. Notably, this study found that coppicing plants in late summer rather than in spring, as previous recommendations suggest, can increase phosphorus capture by 300%.

This year, pollinator visitation data will provide a closer understanding of the relationship between pollinator habitat presence and actual pollinator presence. Upon cyclically harvesting some of the above ground plants near the end of each summer, phosphorus is physically removed from the landscape. Agreements were made in 2022 that in future years many of these species, traditionally applied by Abenaki to medicine, crafts and other utilitarian purposes, will be harvest by them as a small step towards the rematriation of their traditional homeland.

Greenhouse Mesocosm Experiment

Rubin’s team conducted another study looking at mycorrhizae’s efficacy in high vs low phosphorus soil and its efficacy in supporting native shrub growth through a greenhouse mesocosm experiment. Mesocosms are enclosed environments that mimic a small part of a natural environment to be observed under controlled conditions. The researchers investigated the effects of three variables on the plant uptake and leaching of phosphorus: soil phosphorus concentration, mycorrhizal presence, and plant species. They measured the phosphorus in leachate, plant uptake, soil, and mycorrhizal presence to assess the magnitude of their effects on phosphorus loss.

The results of the mesocosm study indicate there are differences in phosphorus uptake and leaching between specific plant species, which could be due to their distinct root structures. In this study, mycorrhizae had no effect on phosphorus uptake nor on leaching in the mesocosms. As this was a study with only one plant species per mesocosm, the researchers noted that the symbiotic relationships between the mycorrhizae and plants may have inadequately mimicked the real-world systems where there are often several plants sharing networks of mycorrhizae.

The findings suggest that the initial concentration of soil phosphorus is the best predictor of the onset of leaching. Soils that are highly saturated by phosphorus are not able to store additional phosphorus, allowing excess phosphorus to leach from the soil. This shows that legacy phosphorus (phosphorus already in the environment from centuries of high application rates, soil disturbance, and vegetation removal) has a significant impact on water quality and phosphorus control.

“There are steps we can immediately take to reduce phosphorus leaching from riparian buffers including our cyclical cutting recommendations. However, our modeling suggests using these techniques alone will take too long to remove substantial phosphorus,” explains Rubin. “Upland phosphorus mitigation, such as nutrient management and erosion control, is essential to maintaining water quality function. Decreasing phosphorus application rates in agricultural production will eventually result in phosphorus load reductions to buffers and water bodies.”

The experimental process applied here can serve as a blueprint for scientific studies that aim to move from conventional research that does not consider Original Peoples or their knowledge towards a more holistic approach honoring and reciprocally collaborating with Original People. Rubin and Görres suggest this form of decolonized research addresses both the social and ecological damage it is trying to repair.

The scientists’ ongoing research experiments with native perennial plants supported by native, local mycorrhizae communities to improve phosphorus uptake, pollinator habitat, and Original Peoples’ traditional uses. While understanding phosphorus dynamics is important to tracking their role in water quality control, Rubin and Görres found that riparian buffer management alone will not reverse the phosphorus pollution causing eutrophication. A more holistic approach to learning about the efficacy of these innovative strategies could translate into watershed resilience when accompanied by restorative upland management adjustments.