Rising to the challenge
Salt marsh restoration to heal historic wounds and combat sea-level rise
The shovel sliced down through the layers of grasses, tough roots, and slippery peat. Wenley Ferguson, the director of habitat restoration at Save The Bay, dug a narrow, shallow channel to drain excess water off the 11.5-acre marsh at Winnapaug Pond in Rhode Island. Supervising a crew of volunteers from the Westerly Land Trust, Ferguson was implementing a simple technique called runneling to restore water flow on sections of marsh that are beginning to convert to open water due to lack of drainage.
Volunteers from the Westerly Land Trust dig runnels by hand at the Winnapaug Pond in Westerly, Rhode Island in May 2021. Photo Kit Straley
Salt marsh plants have evolved to survive in a habitat of extremes, lasting through the ebb and flow of daily and monthly tidal cycles. But accelerated sea-level rise, increased storm surge, restricted drainage due to development, reduced drainage, and shoreline hardening have interrupted these natural cycles, pushing the extremes beyond the physiological limits of the plants. And without plants, marsh habitats begin to sink and wash away. Healthy coastal marshes act like sponges, absorbing the influx of water from storms and buffering shoreline communities from flooding and erosion. Without the plants that make the marsh platform stable, those natural benefits are lost.
Communities of salt marsh-adapted plants like these contribute to the stability of the marsh. Photo by Lauren Owens Lambert.
The stress and die-off of marsh plants followed by loss of elevation is called marsh subsidence. Without the root systems of salt marsh-adapted plants to hold sediments in place, the valuable sediment that contributes to the marsh platform washes away. As vegetated areas convert to open water, the waterlogged marsh subsidence trajectory continues in a harmful feedback loop.
Ferguson highlights the locations of previous standing pools of water that were runneled in Quonochontaug, Rhode Island. The bright green areas are remaining algae from algal blooms in the standing pools. Over time, marsh plants will re-colonize the area and the algae will die off. Photos by Lauren Owens Lambert
Ferguson’s runneling projects occurring at Winnapaug Pond and other locations through Save the Bay aim to stop that loop in its tracks. Save the Bay is part of a network of conservation partners--including the U.S. Fish and Wildlife Service--that is working to restore and protect Atlantic Coast marshes using a suite of innovative restoration techniques. Runneling, ditch remediation, microtypography islands, and sediment placement are restoration techniques that could yield the highest benefits – for wildlife and for people.
A small bird signals big problems
As marshes subside, critical wildlife habitat for uniquely adapted species also disappears. One of these species is the saltmarsh sparrow, a small songbird with dappled feathers, a striking white breast streaked with brown, and a radiant orange face. Within the soft bed of marsh grasses, female saltmarsh sparrows weave teacup-sized nests on the ground to house their eggs and young. In a grassy plain without trees or many shrubs for cover, low nests are key to avoid detection by predators. The sparrows, however, must strike a delicate balance; if they choose a site that is too low, the nest will flood as the tide comes in. For centuries the pressure of predators above, and tide below, shaped the habitat of the sparrow.
An adult saltmarsh sparrow. Photo by Peter Paton
As increased water levels from accelerated sea-level rise and storm surge inundate marshes, the tiny, speckled eggs laid by these sparrows are washed out of the nest on a cold wave, or their young chicks drown, unable to escape the influx from tides. Many nestlings do not survive to make it out of the nest. Because of this, scientists estimate the sparrow population is declining by roughly 9% each year.
A flooded saltmarsh sparrow nest with four eggs. Photo by Bri Benvenuti, USFWS, taken during research activities.
With their life cycle so tightly bound to the processes of a healthy marsh, the plight of the saltmarsh sparrow signals that the tidal marshes they call home are in trouble. The Service and partners are therefore working to restore the natural processes of water flow and drainage on marshes to maintain marsh elevation in the face of sea-level rise. These efforts will benefit not only the saltmarsh sparrow, but all the organisms that rely on salt marshes for habitat and storm protection, including people.
A dry nest with four sparrow chicks. Photo by Bri Benvenuti, USFWS, taken during research activities.
A rock and a hard place
To save the marshes for the future, scientists first must look to the past. The natural processes in salt marshes were interrupted long ago, and that legacy of management is still affecting how marshes function today. Salt marshes of the Atlantic Coast are still feeling the effects of historical modifications to the marshes themselves. Starting in the 1600s, colonial farmers began changing the marshes for salt hay farming by adding ditches and embankments to drain the marshes and ultimately increase hay yield.
A historic painting of salt marsh shows hay farming with bales. Painting by Martin Johnson Heade
Researchers like Dr. Susan Adamowicz, Rachel Carson National Wildlife Refuge’s land management and research demonstration biologist, and Nancy Pau, Parker River National Wildlife Refuge’s wildlife biologist, study the effects of this ditching on the current hydrology of the marsh. So-called mega-pools, large pools of shallow water that would not drain, are growing in number and size in ditched marshes, and vegetation in these once-healthy marshes is slowly dying back.
A historic ditch cuts through the Great Marsh in Newbury, Massachusetts. Ditches appear as straight-line cuts through the marsh platform, often radiating out from a natural channel. Photo by Lauren Owens Lambert
While a comparison of historic land records and Google Earth imagery reveals a widespread pattern of historic ditching along with embankments and mega-pools forming up and down the coast, those changes are not always easily detected at ground level.
Google Earth aerial imagery of Parker River National Wildlife Refuge and the surrounding marsh in Newbury, Massachusetts, shows the pattern and intensity of historic ditching. Ditches are the straight lines radiating out from the sinuous channels, with two (of many) sections highlighted in white to illustrate.
“Legacy alterations don’t readily appear today,” Adamowicz said. “That’s the kicker. We’ve been walking these marshes for decades and never seeing what was right beneath our feet.”
Healthy salt marsh habitat. Photo by Becky Longenecker, USFWS
Innovative restoration: techniques on the rise
Runneling is one of several recommended techniques to restore salt marshes. In addition to runneling, ditch remediation is also sometimes appropriate to restore hydrology, while sediment placement using dredged material is another marsh restoration technique to directly increase marsh elevation. Deciding which technique is appropriate depends on the resources available and the local setting and conditions of the marsh in question. “Literally the work I’m doing just needs either a shovel or a low-pressure excavator and doing the project in phases to prevent excessive drainage and loss of sediment from the marsh surface,” said Save The Bay’s Ferguson. Standing water on the marsh at Winnapaug Pond in Westerly, Rhode Island in June 2020 before runnel excavation, runnel being dug by hand at the same site in spring 2021 , the same site post-runneling in early and late spring 2021. Photos by Save The Bay and Lauren Owens Lambert
By connecting areas with unwanted standing water to channels in the marsh, runnels allow a slow drainage process with limited negative impact on the surrounding marsh platform. At Parker River National Wildlife Refuge in Massachusetts, biologist Pau has been closely monitoring the mounds made by excavated peat from runnels dug in 2019. By the fall of 2019, the mounds were already 50-70% vegetated, and by summer of 2020, they were completely covered in marsh grasses favored by the sparrow. By providing small local patches of higher elevation in the marsh, biologists are hoping sparrows will successfully nest there above the threat of rising tides. “I’ve been in the marsh and flushed sparrows from the [microtopography] islands, but we haven’t found nesting just yet,” said Pau. In ditch remediation, historic ditches are slowly filled with cut marsh vegetation and sediment. Geoff Wilson Principal, Northeast Wetland Restoration, has pioneered this technique with partners, filling the ditches slowly from the bottom up. Cut salt marsh hay is rolled and raked into ditches, where it is then tamped down and held in place with twine. Over time, sediments become trapped in the material, and peat slowly builds.
The steps to ditch remediation. Northeast Wetlands Restoration’s Geoff Wilson cuts the marsh grasses using a specialized machine. Refuge staff use leaf blowers to roll the hay into the ditch, where it is tamped down (third image). The Service’s Dr. Susan Adamowicz, follows and ties the new fill material down using stakes and cord, so the hay does not wash out with the tide. Photos by Lauren Owens Lambert and Kit Straley
“A lot of attempts to fill ditches usually don’t work well because there is inconsistency between the fill materials and adjacent peat,” Wilson said. By using the natural materials to knit the sides of the channel together, after several years of treatment the bottom of the ditch is high enough for sunlight to reach it and for plants to grow.
A natural fill material, salt marsh grasses are cut and rolled to fill in the ditches. Over time, sediments will become trapped in the cut grasses and peat will build from the bottom up. Photo by Lauren Owens Lambert
“We do a little bit of work for three years, and then natural processes do the heavy lifting,” Wilson said.
Finally, sediment placement projects (also called “beneficial use” projects) involve spreading a layer of sediment across the marsh surface, typically using clean dredged materials from nearby navigation channels. The goal of sediment placement is to increase the elevation of the marsh, but the recovery process takes time. In the winter of 2018-2019, 68,000 cubic yards of sand were dredged from the Quonochontaug Breachway in Charlestown, Rhode Island and applied to the marsh. Marsh plants are slowly reestablishing at the placement site including early colonizers like pickleweed, spike grass, and salt marsh hay. Based upon a similar project at Ninigret Pond in Charlestown, Rhode Island, Ferguson estimates revegetation will take up to five years.
Ferguson highlights the natural revegetation at a sediment placement site in Quonochontaug, Rhode Island. As the tide brings in dead plant material, or wrack, and drops it on the marsh, seeds from the plants are deposited. Photo by Lauren Owens Lambert
“We’re building the marsh of the future,” said Ferguson, “and I estimate this process will take about a decade. It’s not a one and done kind of project.”
A series of photos from Quonochontaug, shows the area pre-sediment placement in 2018, immediately after sediment placement in January 2020, and after placement in August 2020. Partners on this project include the Save the Bay, the Coastal Resources Management Council, and Brennan Dredge; funding provided by the National Oceanic and Atmospheric Administration. Photos by Save the Bay
