Agroforestry Phytoremediation Buffer Systems in the Great Lakes Basin

The Laurentian Great Lakes Basin of eastern North America is the largest surface freshwater ecosystem in the world, containing 20% of global freshwater supply and 95% of the United States’ surface freshwater. As a result, the Great Lakes provide substantial provisioning, regulating, supporting, and cultural ecosystem services throughout North America. Potential impacts to these ecosystem services have increased in recent decades, which is consistent with worldwide losses of ecosystem services resulting from land use changes (LUCs). Such LUCs have disrupted terrestrial water cycles and impacted water quantity and quality across the Great Lakes Basin.

The Great Lakes Restoration Initiative (GLRI) was established in 2010 to protect and restore Great Lakes ecosystems from many threats, including those attributed to pollution from landfills, brownfields, and similar sites. Nonpoint sources like these contribute pollution via runoff (aboveground) and leakage (belowground) that can negatively impact nearshore health. Since 2010, the GLRI has funded over 5,000 projects throughout the basin. From 2016 to 2021, the GLRI funded one of these projects led by Northern Research Station scientists. The work continues today and has resulted in the development of the world’s largest regional phytotechnologies network consisting of 16 agroforestry phytoremediation buffer systems (i.e., phyto buffers) in the Lake Superior and Lake Michigan watersheds.

Key Findings

• Over 20,000 trees consisting of 16 poplar varieties and 8 willow varieties have been established across the agroforestry phytoremediation buffer network based on greenhouse results during phyto-recurrent selection testing. Survival rates have remained high, averaging greater than 95% for both poplars and willows throughout establishment.
• Biomass production varies greatly among hybrid poplar and willow varieties. Across all 16 agroforestry phytoremediation buffers, average biomass production of poplars was highest for clone ‘NM5' and lowest for clone ‘NC14106’.
• Generalist varieties with superior establishment across a broad range of buffers and specialist clones uniquely adapted to local soil and climate conditions have been identified.
• A clone developed by the University of Minnesota-Duluth, Natural Resources Research Institute exhibited substantially higher daily water use than other clones. Such enhanced water use could be utilized to maximize the effectiveness of phytoremediation systems.  

Our Research

Phytoremediation, which is the use of plants to clean up contaminated soil, sludge, sediment, or groundwater, is the most common of all phytotechnologies, with remediation processes depending on contaminant type (inorganic versus organic) and ecophysiological mechanisms involved. Poplars and willows are ideal tree species for phytoremediation because they grow quickly, propagate easily, and have extensive root systems and hydraulic control potential, all of which enable them to serve as biological systems that mitigate, capture, and remediate pollution. 

 To establish the phytotechnologies network, we used phyto-recurrent selection to choose superior poplar and willow genotypes belonging to two categories: 1) generalists that remediate a broad range of contaminants across sites, and 2) specialists that are matched to specific pollutants and site conditions. Our newest results identify poplar clones belonging to both of these groups with maximum phytoremediation potential (see below). These data are useful for clonal selection to maximize ecosystem services in future phytotechnology applications, regardless of specific site conditions or genotypes deployed. Using generalists and specialists enhances the potential for phytoremediation best management practices that are geographically robust, being regionally designed yet globally relevant.

Expected Outcomes

In temperate zones, poplars and willows contribute multifunctional ecosystem services, combining environmental restoration, land reclamation, and feedstock production for bioenergy and paper production, thus increasing environmental sustainability and livelihood for communities across the rural to urban continuum. The application of phyto buffers to lands within the Great Lakes Basin helps to reduce the uncertainty about the efficacy of using poplars and willows to remediate landfills, brownfields, and similar sites, with the long-term goal of providing landowners and site managers with environmentally-friendly treatment options. To this end, hundreds of superior poplar and willow varieties have been tested and dozens matched to soils and climate at the phyto buffer sites in Wisconsin and Michigan to provide societal benefits such as: water quality improvement, stream bank stabilization, forest cover enhancement, and ecosystem restoration. 

Research Results

To date, we have published 9 peer-reviewed manuscripts and given 90 presentations about these agroforestry phytoremediation buffer systems: 3 international keynote addresses (Argentina, Serbia, Sweden), as well as 62 oral presentations and 25 posters (Canada, Germany, Italy, Serbia, USA). In addition, in June 2022 we hosted Phyto Day, an outreach and networking event on phytotechnologies. Participants had the opportunity to network with phytotechnology experts from government, academia, and industry, and learned about state-of-the-art phytotechnology research being conducted at these agroforestry phytoremediation buffer systems.