An unexpected and delightful experience during the American Society of Civil Engineer’s LID Conference in Maine was meeting Kate Kennon, co-author of the great reference book Phyto and Owner of Offshoots, Charlestown, Massachusetts.
Phyto translates the body of science around phytoremediation into usable guidance and insights for landscape architects, field engineers and anyone that wants to tap into the power of plants for phytoremediation. The book has “generated a bit of a buzz,” Kate said. In the year since its introduction she’s traveled around the country speaking to create more understanding of phytoremediation and phytotechnology. See the review in NewTerrain last fall.
A landscape architect by training, Kate first became interested in how plants can remediate sites when she worked on a gas station conversion project in Barnstable, Massachusetts. The city wanted to convert the site into a park and the engineer also wanted to bundle stormwater management into the project. The project began Kate’s 8-year educational odyssey ultimately resulting in the book Phyto.
Just a few of the bullets Kate offered the LID Conference audience in a seminar below provide a quick guide to using plants for phytoremediation.
- Erase sunflowers as a pollutant mitigation. In greenhouse studies they showed promise to mitigate lead, but under field conditions lead is so heavily bound to the soil that they are ineffective. Yet using sunflowers to take up pollutants is ubiquitous on the internet.
- Some soil contaminants are good opportunities to use plants, some situations have potential and many situations are not suitable for phytoremediation. In those situations where plants can be helpful, they can help to clean up a site, or even mitigate potential problems. She encouraged everyone to think of pollutants as either organic compounds that plants can degrade or inorganic compounds that are not degradable, but must be extracted—like nickel, arsenic, selenium, cadmium or zinc. Plants may be able to help, but not necessarily solve inorganic problems.
- Think of plants complexly in 3-D: Root depth and plant structure. Plants with long, deep tap roots are known as phreatophytes. These deep-rooted species are used over and over again in the phytoremediation literature she said. You also want plants with high respiration, which is why poplar is used over and over she said.
- Phyto includes plant lists for every contaminant if the plant has been proven to be good for remediation.
One specific plant Kate mentioned for remediation is Pteris vittata, a hyper accumulator of arsenic. Selections known as Victory ferns are available. (Southern readers note: In 1999 the Florida Exotic Pest Plant Council added it to their Invasive Plant List.)
More recently Kate has been working on plants for stormwater systems. “It’s less about species specificity for stormwater and way more about a functioning plant system,” she said. The goal is diversity. Plants in stormwater systems have to survive in engineered media. “If you don’t have a thriving plant community it’s a non-starter.” That leads to the second plant Kate mentioned for functional landscapes and phytoremediation: Willows.
One of the most underutilized plants for stormwater BMPs are willows, she said. They are deep rooted and are good at transpiring water. They also degrade many organic compounds and can help mitigate some metals. The wide range of native willows includes a range of bark and foliage types. The attitude among many L.A.s she said is that willows are “weak-wooded and short lived.” However, “the landscape is not architecture. It’s dynamic, it moves. Some plants may be a nurse crop for what comes behind.”
Phyto is great investment. If you ever get the chance to enjoy Kate Kennen’s company at a meeting, do it. She’s fun to talk to and tapped into some very interesting stuff.
NewTerrain October 3, 2016.