The Oldest Eco-tech: Trees

We need a machine that can clean pollution out of the ground and the water table. It has to suck the bad stuff (pollutants) out and leave the good stuff (water and dirt) in. Then, somehow, the machine needs to break the poisonous molecules into smaller, harmless ones, thus recycling pollutants without producing any additional waste in the process. One imagines a tangle of tiny tubes linked to sensors, vials, and off-gas valves—an ecological engineer’s lifework, perhaps.

But environmental scientist Elizabeth Nichols and her graduate student Rachel Cook think the fantastic machine already exists: it’s a tree.

The state of North Carolina approached Nichols with the same problem in the mid-90’s. A World War II Air Force depot near Elizabeth City had been dismantled. The work uncovered concrete bunkers under the tarmac, and the bunkers were slowly seeping their contents—150,000 gallons of jet, diesel, and gasoline airplane fuel—into the surrounding soil. The fuel occupied the first level of water table, a mere 7 feet beneath the soil.

And the tarmac was about 100 meters from the Pasquotank River.

“The question was first how to slow the seepage down, then ultimately how to draw the pollutants off the water table. And how to do it without disturbing the surrounding ecology even more,” Nichols said.

Her answer was phytoremediation—an application that uses plants as well-designed eco-tech. Nichols and her collaborators (USGS, NCDENR, and US Coast Guard) planted poplar, willow, and pine trees to slow groundwater seepage, slowly draw the diluted fuel from the groundwater, and then release the broken-down fuel, in the form of hydrogen and oxygen, into the air.

“Jet fuel isn’t good for trees,” Nichols said, “and you can see bare spots where the soil is saturated.” But trees like the willow pull water off the top of the water table, where lighter jet fuel floats. Nichols and Cooks’ results imply that the trees have had significant impact on pollutant levels since 2006.

Phytoremediation as a major means of ecological remediation hasn’t been widely accepted, yet. This study serves as a demonstration site for North Carolina-- consideration of a holistic and far-seeing approach to an immediate threat to resources. Nichols and Cook want to prove that such foresight can be successful.

The study is funded by the EPA and North Carolina’s Department of Natural Resources’ 319 program to clean surface water. Cook’s paper describing the current state of groundwater at Elizabeth City site will be published in the next issue of the International Journal of Phytoremediation, due out later this year.