Agriculture has played an important role in the history of coastal Massachusetts and the land has marks to show for it. Some of these marks come in the form of man-made ditches that crisscross the landscape — including marshland.
Ditching done for salt hay farming or mosquito control also disrupted natural processes that otherwise maintain marsh hydrology and elevation.
The ditch remediation technique is used on these newly mowed and filled salt marsh ditches in the Great Marsh. Two bailing twines on stakes keep the rolled hay in the ditch. Credit: Burdick, Peter, Moore, Adamowicz and Wilson
David Burdick, University of New Hampshire Associate Research Professor in Coastal Ecology and Restoration, says ditches allow excessive draining and ultimately cause the marsh surface to sink. The peat — soil-like material consisting of partly decomposed vegetable matter — between these trenches oxidizes and carbon is released into the atmosphere, making the marsh more vulnerable to impacts from storms and sea-level rise.
That’s why Burdick and other partners are working with the U.S. Fish and Wildlife Service to help raise the floor of several man-made ditches using an innovative technique called ditch remediation. The technique, piloted in 2008 at Rachel Carson and Parker River National Wildlife Refuges, is now being applied at multiple refuges with ongoing Hurricane Sandy resilience projects.
One of four salt marsh ditch sites is treated as part of a project supported by Hurricane Sandy resilience funding. Vegetation is cut in green areas, and rolled into ditches shown in red. To ensure sufficient drainage, not all ditches are filled. Credit: Burdick, Peter, Moore, Adamowicz and Wilson
In fall 2014, four ditch areas within the Great Marsh were chosen for remediation. The process involves cutting vegetation from higher marsh areas, raking it into the low ditches and holding the grasses in place with twine. Nancy Pau, Wildlife Biologist at Parker River National Wildlife Refuge, says this process will help peat to grow within the ditches to the point where vegetation can get established and allow the whole system to begin to store more carbon.
Pau says the remediation process will raise the elevation of the ditches to approach the level with the marsh surface. “The goal is to get the entire marsh surface to elevations that allow the marsh peat to rebuild,” she says. “We are basically helping the marsh ‘heal’ these ditches faster.”
Treatment for the 2015 season is now completed at Parker River, part of a broader effort to restore Massachusetts’ Great Marsh, one of the largest tidal marshes on the Atlantic Coast.
“The goal of the project is to increase resilience to climate change by removing man-made stressors associated with salt marsh ditching,” says Susan Adamowicz, the Salt Marsh Land Management Research and Demonstration Biologist with the Service and expert in marsh ecology. “Over time, as sediment builds up and plants begin to grow, the ditches should disappear.”
Accumulation of sediment and marsh grass, or Spartina alterniflora, colonized in a remediated ditch in summer 2015 (less than 1 year from initial treatment). Credit: Burdick, Peter, Moore, Adamowicz and Wilson
Burdick says the remediation process adds anywhere between 5-10 centimeters of elevation to the ditch floor with each growing season. Measurements before treatment showed the ditches to be 75 centimeters (2.5 feet) deep, which is low compared to where the marsh surface once stood. The goal elevation is zero centimeters, which will match the natural platform of the marsh.
“We expect several years of treatment will be required to see regrowth of marsh grass,” Burdick says. He hopes to see another 10 centimeters of elevation rise in treated ditches after this season’s work and complete re-vegetation of the shallower ditches.
While the progress may be small, Burdick says he and his team are encouraged by the outcome of the first year’s effort, showing increased elevations of 5-20 centimeters on treated ditches in just 6 months.
According to Burdick and other project leaders, Hurricane Sandy recovery funding will support continued monitoring of growth and elevation through 2016. New funding sources will be sought beyond then to determine how long it takes for the deeper ditches to completely fill in with newly created peat and whether the remediation process has the ability to raise overall marsh elevation to pre-ditched levels.
To learn more, visit the Parker River National Wildlife Refuge website.
U.S. Fish and Wildlife Service Northeast Region 