A sweet solution to a sticky problem
When you’re a biologist at a site named for a legendary environmentalist, you feel a responsibility to do your job with the planet in mind.
Just ask Dr. Susan Adamowicz, Land Management Research and Demonstration Area biologist for the Northeast Region of the Fish and Wildlife Service. Stationed at Rachel Carson National Wildlife Refuge in Maine, she is tasked with finding innovative ways to manage wildlife habitat and takes inspiration from the renowned author.
In 1962’s Silent Spring, Carson, who also worked for the Service, sounded the alarm about pesticides that imperiled wildlife and people alike. She knew that many of the synthetic chemicals used to control unwanted plants and insects were dangerous to more than their targets.
For a healthy environment, Adamowicz seeks other solutions … and hopes she has found one with the help of a University of New Hampshire researcher.
A “Consummate Invasive Species”
Phragmites australis, or common reed, is an aggressive, nonnative marsh grass that pushes out native wetland plants. You’ve probably noticed its tall (up to 18 feet!), feathery, golden stalks in your neighborhood or along the freeway.
Phragmites is plentiful in the high salt marsh of the Great Marsh, the largest continuous stretch of salt marsh in New England. Three thousand acres of the 20,000-acre marsh in eastern Massachusetts lie within Parker River National Wildlife Refuge.
Phragmites changes the structure of the salt marsh, filling natural channels and tidal pools where waterbirds, fish, and invertebrates find food and safety. Many wildlife species find its dense patches impassable, and in the fall, when the stalks die back, stands of the plant turn to tinderboxes primed for wildfire, putting nearby homes and businesses at risk.
Biologists have long searched for effective ways to control Phragmites. It’s a determined adversary, however. Like those birthday candles that re-ignite, just when it seems defeated, it springs back to life.
According to Adamowicz, “Phragmites is the consummate invasive species. If you cut it or burn it, it comes back. If you can flood it for six months, that might kill it, but flooding is not always feasible.”
While restoring natural tidal flow to coastal marshes is the preferred way to fight Phragmites, replacing culverts, filling ditches, and improving drainage can take a long time. Treating it directly is necessary to keep it in check in the meantime.
Sadly, there’s been no good way to do that. Herbicides work in certain locations but pose a risk to native vegetation and groundwater — certainly not a solution Rachel Carson would embrace.
So Adamowicz teamed up with Dr. David Burdick, research associate professor and interim director of the Jackson Estuarine Laboratory at the University of New Hampshire, to explore innovative ways to control Phragmites. One of the methods they tested was sweet and simple.
Turning the Tables
Burdick had a hunch that sugar, the same kind you put in your coffee, might be Phragmites’ Kryptonite.
Each summer, rising air temperatures and increased plant growth stimulate bacteria in salt marsh soils to convert organic matter and oxygen into carbon dioxide, water, and energy — a process called aerobic (“with air”) respiration. The activity quickly uses up soil oxygen, forcing other groups of bacteria to make energy using anaerobic (“without air”) respiration.
One by-product of anaerobic respiration is hydrogen sulfide gas, a potent toxin for plants as well as people. At typical levels, the gas is not deadly to most native plants, but it can be toxic to Phragmites.
Burdick thought increasing bacterial respiration, and therefore hydrogen sulfide levels, could kill the invasive.
“Because Phragmites is a master at getting oxygen to its roots for its own respiration, we could use this strength to kill it,” he mused. “By elevating soil hydrogen sulfide levels, we might stimulate the plant to oxidize the gas into a strong acid that it may not be able to tolerate.”
While he couldn’t control air temperatures, he could increase fuel for the bacteria — using glucose in the form of table sugar.
Pour Some Sugar on It
Burdick and his team first tested their idea in the greenhouse. They soaked Phragmites plants with bay water for three hours every two weeks to mimic the flooding that high-marsh plants get during the extra-high “spring” tides that come with the full and new moons each month.
Some plants (the control) received only the bay water; others got water with table sugar; still others water with extra salt; and the remaining, water with sugar and salt.
Both the sugar and sugar-and-salt treatments showed signs of stress within weeks and eventually died. Only the plants that received plain bay water or bay water with added salt lived.
The sugar-treated plants had very high soil acidity, possibly caused by sulfuric acid, the product of hydrogen sulfide oxidation. This supported Burdick’s theory.
Next, Burdick and Adamowicz headed to Parker River Refuge to set up a field study in the northern part of the Great Marsh. The research was supported by federal funds for Hurricane Sandy recovery and resilience projects.
They isolated individual Phragmites plants and applied the same treatments as in the greenhouse. Sugar and salt were put on the plants every two weeks, after the spring tides flooded the marsh.
The plants that got sugar had far greater mortality than the other treatments, even with uncontrollable environmental factors, such as rain — a clear sign that sugar is not sweet to Phragmites.
Refining the Technique
Adamowicz is pleased with the study results so far and eager to set up more field trials. She’s exploring ways to treat Phragmites with sugar and salt more efficiently and broadly, perhaps using a backpack sprayer to apply corn syrup at more-frequent intervals than every two weeks.
“This is another tool in our toolbox, and it’s nontoxic to wildlife, which is very desirable,” she said. “The more complicated response to Phragmites is ecosystem restoration, but in the meantime, we need a fast-acting tool to help native plants come back and buy time.”
If Rachel Carson were alive today, she would certainly approve of this environmentally sound method — and just might be thinking, “Sweet!”
When this story was originally published in Spring 2018, it generated a surprising number of comments — and they’ve kept coming. Apparently, Phragmites is on everyone’s least-wanted list!
Many readers were eager to give the method a try and wanted more details.
It’s important to note that the treatment is applicable only to saltwater systems. The process depends upon high concentrations of sulfate, which is in seawater but not freshwater. Sulfate is the second most common salt in saltwater (after sodium chloride).
In the greenhouse portion of this research, the plants were watered with bay water whose salinity was 15 parts per thousand. In the field studies, the water source was an adjacent creek, with salinity of 14–23 ppt.
Dr. Burdick says, “If you have a reasonable amount of seawater (15 ppt) you should have enough sulfates for the sugar to work. You should add about 0.4% table sugar by water volume of the root zone — that would generate sulfides.”