Brine -- water saturated with three to 10 times more salt than seawater -- is toxic to plants. Without human intervention, it can take years for the saline content in the soil at a spill site to return to levels that allow plant growth.
But researchers found that knotweed, a member of the Buckwheat family, grows well in high-saline soil, and actually helps to remove the salt so that other plants can once again thrive.
"When companies drill for oil, they also get brine, and the brine is usually stored in a tank on the site," said Irwin Ungar, professor of environmental and plant biology at Ohio University and co-author of the study. "At the site we studied, the brine spill occurred in 1989 when workers were pumping the salt water out for storage."
The following year, researchers began studying the site, about 15 miles northeast of Athens, and noticed that while all vegetation on the site was dead, knotweed was growing on the periphery. Four years later, when the saline content was still 1 to 2 percent above normal, the knotweed was thriving inside the spill area.
Soil tests proved that the plant had helped to reduce the saline content of the soil. Researchers believe that the site will be returned to its pre-spill state with the aid of the plant's natural saline-removing ability and rainfall that helps to dilute the salt content. The knotweed studied, Polygonum aviculare L, is a ground-covering leafy plant speckled with small pink flowers. It's related to Japanese knotweed, a much more aggressive weed that creates problems for gardeners around the country.
Although knotweed is not as saline-tolerant as plants found in salt marshes and other coastal areas, its wide habitat range would make it an ideal candidate for efforts to restore contaminated soil naturally and inexpensively, Ungar said.
"Currently, soil contaminated by brine must be removed and landfilled," he said. "Using this or some other saline-tolerant plant to remove salt from the soil through natural means would be more environmentally and economically desirable."
The research was co-authored by Margaret Foderaro, a former Ohio University graduate student in environmental and plant biology. It was supported by the Petroleum Environmental Research Forum and appeared in a recent issue of the journal American Midland Naturalist.
Contact: Irwin Ungar, 614-593-1120; iungar1@ohiou.edu.
Written by Kelli Whitlock, 614-593-0383; kwhitlock1@ohiou.edu.