(Editor’s Note: This article was originally published on July 28,2010. Your comments are welcome, but please be aware that authors of previously published articles may not be able to respond to your questions.)

What, precisely, is phytoremediation?

Enough etymology. Simply put, phytoremediation is the use of plants to clean up environmental pollution in soil and water. Contaminants include metals, pesticides, fertilizers, and–our biggest worry at the moment-crude oil. These plants also help to prevent weather and groundwater from transporting pollution away from a polluted site to other areas.

How does it work?

Certain plants have the amazing ability to break down pollutants or contain and stabilize them by acting as filters or traps. In most cases, this involves the root system of the plant. Roots in these plants provide a very large surface area to absorb and accumulate not only nutrients essential to growth, but also most contaminants. These are either stored or broken down into benign compounds.

The use of trees in this process is gaining popularity, primarily because of their extensive and deep-seated root systems. Their roots can more effectively trap and absorb pollutants, even those that leach down into ground water many feet beneath the soil surface.

Case in pointThe use of poplar trees (Populus spp.)– or any other tree for that matter–in phytoremediation was pioneered by Lou Licht, a graduate student in Civil and Environmental Engineering at the University of Iowa. In 1991 he planted a test plot of 11,000 poplar trees along a creek that serves as drainage for the surrounding farm fields about eight miles from my home in South Amana. The creek drains directly into a local lake called simply “The Lily Lake,” because of its lotus lilies and their spectacular bloom in July and August. See photos of plaques at right for further information.

Licht’s experiment was a great success, and proved instrumental in boosting the recognition and fortunes of his company, Ecolotree, founded in 1990. It has the distinction of being the oldest phytoremediation firm in the world.

Why use poplars?

o Greater than 25 species worldwide (Species most commonly used in phytoremediation include P. deltoids, P. trichocarpa, P. simonii, and P. nigra.)
o Fast growing (3 to 5 meters/year)
o High transpiration rates (100 liters/day optimally for a 5 year old tree) for drawing moisture and contaminants from the soil
o Not part of the food chain
o Can be used for paper production or as biomass for energy
o Relatively long-lived (up to 30 years)
o Easily grown from cuttings
o Can be harvested and then regrown from the stump
o Can extend roots down to the water table and pump from the zone of saturation, making them natural solar-driven pump and treat systems.

A lone Canadian Goose paddles among the lily pads, and Trumpeter swans enjoy the peacefulness of a cove at the Lily Lake. Wildlife now flourishes in the lake and its surroundings as never before. New species since the onset of the phytoremediation project include a multitude of Canadian Geese, wild Trumpeter Swans, Bald Eagles, otters, and mink. Other denizens include muskrats, turtles, and many different species of birds and fish. Fishing is not a common activity at the lake, since the waterlilies cover almost the entire surface of the water for most of the season.