Shifts in Soil Bacterial Populations Can Indicate Wetland Restoration Success, Study Shows
A study led by researchers at Duke University finds that restoring degraded wetlands—especially those that had been converted into farm fields—actually decreases their soil bacterial diversity.
But that’s a good thing, say the study’s authors, because it marks a return to the wetland soils’ natural conditions.
“It sounds counter-intuitive, but our study shows that in restored wetlands, decreased soil bacterial diversity represents a return to biological health,” says Wyatt H. Hartman, a PhD candidate in wetlands and environmental microbiology at the Nicholas School.
“Our findings are novel because they are the opposite of the response seen in terrestrial ecosystems, where restoration improves conditions from a more barren, degraded state,” says Curtis J. Richardson, director of the Duke University Wetland Center and professor of resource ecology at the Nicholas School.
Their paper was published in The Proceedings of the National Academy of Sciences in October 2008. Richardson is Hartman’s faculty advisor.
Soils in undisturbed wetlands present harsh conditions with low pH, oxygen and nutrient availability in which fewer bacterial groups can survive and grow, the researchers explain. In comparison, former wetlands that have been drained, limed and fertilized for farming host greater soil bacterial diversity because they present conditions more suitable for bacterial growth.
“The bacterial communities in these fields almost resemble those found in wastewater treatment plants,” Hartman notes.
Soil bacteria are essential to wetland functions critical to environmental quality, such as filtering nutrients and storing carbon.
“The mixture of bacterial groups in wetland soils can reflect the status of wetland functioning, and the composition of these populations is as telling as their diversity,” says Richardson. Measuring whether the right mix of bacteria is returning to a restored wetland can be a valuable biological indicator scientists can use to evaluate restoration success, he says.
Often called the “kidneys of the landscape,” wetlands filter and reduce nutrients and pollutants from agricultural and urban runoff, improving water quality. They store 20 percent to 25 percent of the world’s soil carbon, while covering only four percent to six percent of its land mass.
While more than half of original wetland acreage in the United States has been destroyed or degraded, tens of thousands of hectares have been restored in recent decades as a result of the federal government’s “no net loss” policy.
“Re-establishment of microbial communities indicates a restoration of the biological functions of soils. This study across a wide range of wetlands is the first to establish that shifts in soil bacteria populations may be a key marker of restoration success,” Richardson says.
Rytas Vilgalys, professor of biology at Duke, and Gregory L. Bruland, assistant professor of soil and water conservation at the University of Hawaii at Manoa, are co-authors on the paper. Bruland received his PhD from the Nicholas School in 2004; Richardson was his faculty advisor.
The study was funded by a Duke University Wetland Center Case Studies Endowment and a National Science Foundation Graduate Research Fellowship.
