Randall’s Island salt marsh restoration a model for urban renewal

Manhattan was once a dense, natural habitat and home to diverse ecosystems for numerous species of animals. However, with urban development, Manhattan has become the antithesis to anything one would ever consider “natural.” Fortunately, in recent years, New York City has taken steps to improve and incorporate nature into its urban sprawl. One step in that process has been the restoration of a salt marsh on Randall’s Island along a shoreline plagued with deteriorated seawalls and littered with construction debris. The restoration project utilized some of the most up-to-date landscaping and environmental technologies, and this salt marsh has now begun to regenerate back to its original state – providing New York residents with a fantastic outdoor recreational resource and serving as a model for urban renewal and revitalization.

Great Ecology & Environments, Inc. (GEE), a leading environmental consulting agency headquartered in New York, spearheaded the salt marsh restoration project. Members of GEE conducted a site assessment and analyzed soil, water and debris samples for contaminants. This informed the development of a design that excavated fill material down to intertidal elevations to allow high tides to inundate the restoration site; replaced invasive plant species with native species; and encouraged the growth of native salt marsh grasses. This will provide an improved habitat for wildlife, and the planted salt marsh will provide a shoreline buffer to help prevent erosion. Natural filtration from the salt marsh to non-point source pollution into the Harlem River, East River and Long Island Sound will improve the water quality and foster a healthy New York ecosystem.

New York residents can now explore an authentic salt marsh habitat right in the midst of their dense urban landscape.

Core goals of the project

According to Sarah Welch, ecologist with GEE, the project originated when the New York City Department of Parks and Recreation was required to perform a mitigation project in order to offset the construction of a bicycle and pedestrian path in Riverside Park, Manhattan. The project called for the addition of salt marsh to the north end of Randall’s Island, and the goal was to replace the original function of impacted wetlands through construction of this one-acre salt marsh.

“There are many metrics to determine success of a salt marsh restoration,” said Welch. One common metric is whether 85 percent of the plants placed in the sediments survive, Welch added. Salt marsh plantings generally display a strict zonation due to the physical stresses of their environment. Therefore, close attention was paid to elevations that determine the hydrology of the site and, thus, the planting pattern.

 According to Welch, one priority of the project was finding a way to reduce the wave energy from the Bronx Kill and East River. This energy comes from currents, tides, boat wakes and storms, and can hurt plant survival and erode marsh.

“We also needed to design a salt marsh that resisted invasive species – especially common reed (Phragmites australis),” said Welch.

Community and environmental benefits

According to Welch, the Randall’s Island salt marsh restoration is part of a larger master plan for Randall’s and Wards Islands that includes the construction of multiple sports complexes, as well as numerous ecological restoration projects.

“Projects like this provide excellent educational opportunities, as well as inspiration for revitalization of neglected areas,” said Welch. “Although it is relatively small, the Randall’s Island salt marsh will attract native wildlife and provide an aesthetically pleasing view, enhancing the experience for visitors walking along the future waterfront path adjacent to the project.”

The salt marsh will also increase habitat area for bird species and aquatic filter feeders, as well as potentially act as a nursery for juvenile fish. Over time, local water quality will potentially increase as plantings capture sediments and nutrients, especially as filter feeders start to colonize the marsh.

Once established, the salt marsh serves to buffer the shoreline from storms and erosion, and also protect the Bronx Kill from direct runoff from that area.

Overcoming the challenges

According to Welch, one of the most basic challenges during this project was that construction work was done in a tidal area, and tides therefore dictated construction times — potentially making the work inefficient. The original solution to this problem was to construct a complete riprap berm at the edge of the salt marsh – essentially creating a dike to work behind. At the end of construction, the channels called for in the design would be broken through and the site would be flooded. The remaining riprap berm would be left intact to protect the marsh.

 “However, this solution turned out to be unnecessary because of the amount of work being done in the area already,” said Welch. “In the end, contractors were able to simply work elsewhere on the park site during high tides, and thus they remained efficient and kept overall costs for the entire work site down.”

Wave energy generated by the East River and Bronx Kill also presented challenges to the project.

“Our solution was to build a series of riprap berms to protect the salt marsh from the direct impact of the rivers,” said Welch. “These berms help to shelter the salt marsh.”

There were also issues with getting the exact plant species specified in the design. Substitutions were made in order to get the site fully planted before mid summer, but the replacement species did not fare as well.

“In something as specific as salt marsh restoration, with its precise zonation, we should have made sure earlier that we would be able to get the correct plant species,” said Welch.

Landscaping and environmental technologies and techniques

According to GEE, several of the technologies and techniques used on the Randall’s Island project can be utilized on smaller projects by professional landscapers.

“We used coir mats to prevent erosion,” said Welch. “This is easily used on a smaller scale, and helps keep slopes in place while allowing plants to grow. The mat degrades over time, by which point plantings should be established enough to secure the slope.

“We also went with a low-nutrient sandy loam as a planting soil,” Welch added. “This choice was made as part of our anti-invasive plant strategy. Invasive plants tend to make better use of excess nutrients than native plants. So, by limiting nutrients and planting native species, we hope to give desirable species an edge.”

Incorporating nature back into the city

This salt marsh restoration is part of a growing movement that believes that “nature” can be compatible with “city.”

“In order to achieve this integration, both entities must alter their traditional definitions,” said Welch. “After all, a constructed salt marsh in the midst of New York City is neither ‘natural’ nor ‘urban’ — but a fusion of both. Unlike ecosystems found naturally, urban restoration is subject to the same spatial and monetary constraints affecting all construction in cities. Therefore, like any new building design, the project must be carefully designed and controlled. At a certain point though, we must recognize that this designed system is alive in a way no Manhattan office building is, and, therefore, the urban environment must treat it more carefully than steel and brick.”

According to Welch, New York City officials are recognizing that the importance of green spaces goes beyond a few pretty trees.

“These spaces — whether they are parks or green roofs or constructed wetlands – can directly benefit the city on a structural level,” said Welch. “From reducing urban heat island effects in parks and on roofs to treating and detaining stormwater through wetland restoration, we are learning that traditional ‘nature’ can contribute to the city in an aesthetically appealing and extremely useful way.”

Welch pointed out that the most direct attempts to bring back natural systems once found in Manhattan are several projects proposing to put shellfish, such as oysters and mussels, back into the East River. Prior to modern times, the oyster beds of New York Harbor were full of enough oysters to filter the water of the entire harbor between tides.

“Whether the harbor will ever return to this level of ecosystem function remains to be seen, but it is a perfect example of the growing recognition of the technical roles once played by ecosystems that have been degraded for hundreds of years,” said Welch.

According to GEE, decision-makers in other urban areas can learn from this process and begin to restore the natural ecosystem in their cities.

“The key is to recognize opportunities to introduce ecological systems into traditional infrastructure,” said Welch. “Cities should learn about ecosystems that were native to that area, and what functions they performed, then use this information to develop environmental solutions.”

For more information about GEE and this project, visit www.GEEinc.net

Note: GEE, previously known as Great Eastern Ecology, recently changed its name to Great Ecology & Environments to reflect the company’s broader scope while still remaining true to its original “great” ecological vision.