Bronx River Restoration

In the 1600’s, New York City’s Bronx River was a drinking water source and a sylvan haven for beaver, oysters, and herring. It became blighted as urbanization progressed, reincarnating as an industrial power source, an open sewer, and a garbage dump. Today, landscape ecologists are reconstructing the waterway’s ecological history as a reference point for its restoration effort. Watch conservation teams coax new life into the Bronx River as they restock it with native fish, lay down oyster beds, and remove invasive species along its shores.

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The Past and Future Vigor of an Urban River

In April 1609, English explorer Henry Hudson set sail in his ship the Half Moon in search of a Northwest Passage to the Pacific Ocean. He didn't find it, but along the way he navigated a riverine wilderness he considered "as pleasant as one need tread upon." The region, which would be incorporated as the City of New York 56 years later, was described in lush language by its Dutch settlers: "The country is rolling in many places, with some high mountains, and very fine flats and maize lands, together with large meadows, salt and fresh. . . . It is overgrown with all kinds of trees, standing without order, as in other wildernesses." The Dutch reported that great numbers of bears, elk, wolves, beavers, and bald eagles prowled the bedrock ravines and cool forests. The region's rivers and coasts seethed with salmon, sea turtles, lobsters, and oysters as large as dinner platters.

Of the five New York City boroughs today, the Bronx has some of the city's most significant natural areas. It's more than 25 percent parkland, and the city's largest freshwater river still flows through its heart. Yet because of aggressive urban growth over the last 400 years, the type of landscape described by Henry Hudson has all but vanished along the Bronx River, replaced by expressways, elevated subways, dams, and buildings of steel and concrete.

But there is hope for the Bronx River still. Inspired by a past that hardly seems believable today, teams of scientists, conservationists, and volunteers are working to rebuild what they can of the river's early ecological glory. A functional ecosystem requires many interacting elements, among them flora, fauna, soil, and water, and the restoration effort is addressing these elements piece by piece. Project members are dredging trash, fighting erosion, clearing invasive species, and coaxing native ones to regain a foothold. And they are seeing positive results.

Mapping a History

The Bronx River begins north of New York City in Westchester County. It winds through the Bronx's signature parks—the New York Botanical Garden and the Bronx Zoo—and empties 37 kilometers later into the East River, which links to Long Island Sound. In Hudson's day, the marsh at the mouth of the Bronx River made up 30 percent of the river's watershed, all the land area that drains into a river. "Historically, the vast estuary salt marsh system was so flat," says Marit Larson, an environmental scientist for the New York City Parks Department, "that at high tide, waters would connect from as far east as the Hutchinson River all the way as far west as Manhattan."

"It's really important to look at the past when we think about conservation," says Eric Sanderson, a landscape ecologist with the Wildlife Conservation Society, which operates the Bronx Zoo, "because the world, has, frankly, been diminished by human activity over the 20th century."

Today, only one acre—less than 1 percent—of the Bronx River's salt marsh hasn't been filled in with earth. Most of the waterway's small tributary streams had met the same fate, and their water is now piped. Refuse, untreated sewage, and industrial and household chemicals did and still do pollute the borough's waterways and soil. Most native animals and plants were extirpated—became locally extinct—and were replaced with new, invasive species.

"Restoration is bringing back ecosystems and biological communities to what they used to be in the past," says Sanderson, "or rather, restoring them to their natural ranges of variation." Discovering this range is a main goal of Sanderson's research on the landscape of New York City.

One way he has tracked ecological changes in the Bronx is by studying vintage maps. For the Bronx River project, Sanderson's scoured library collections—including the Library of Congress and London's National Archives—for maps made in the 18th, 19th, and 20th centuries. Cartographers of the warring parties of the American Revolution produced the most detailed early maps. Maps that showed carefully staked real estate developments in the mid-1800s were also choice finds. Of more than 80 documents surveyed, Sanderson selected six that showed the whereabouts of forests, wetlands, and waterways. He then georeferenced them, or aligned their geographic features to within 100-meter accuracy of current-day coordinates, to learn what was once where.

Rebuilding a Future

Sanderson's maps guide where and how the river is being restored. Two groups shoulder most of the fieldwork. One is Larson's Parks Department unit, the Natural Resources Group; the other a nonprofit community organization called the Bronx River Alliance.

It is impossible for the Bronx River ecosystem to be restored to its pristine 1609 condition, but at those locations with less extensive damage, workers hope to reestablish "original" conditions from some baseline in the mapped history. One hopeful site is an abandoned concrete factory about three kilometers upstream from the river mouth. A portion of the site is being reverted to salt marsh. "We had a unique condition at the concrete plant," explains Larson. "One of the structures that was built out into the river originally provided a docking and loading facility. This created a kind of protected zone, with a backwater eddy where sediment deposited." The zone happens to have a gentler, wider slope than any other shoreline in the Bronx River system—prime substrate for marsh. The Natural Resources Group worked with volunteers to remove invasive plants, such as mugwort (Artemisia vulgaris) and the common reed (Phragmites australis), and reestablish native cordgrass (Spartina alterniflora) at the shoreline. They also turned an adjacent hill of concrete rubble into a sand slope and replanted native maritime shrubs and grasses to counter erosion and stormwater runoff at the new marsh. The concrete plant will open as a public park in spring 2008.

South of the concrete plant, at the now-shrunken estuary at the river mouth, carcasses of discarded cars, bedposts, and carpet remnants blemish the water surface. Pollution and overharvesting have reduced the estuary's vast native oyster beds to scattered individuals. Automobile tires, ironically, provide surfaces upon which free-floating juvenile oysters can attach and grow. But time and urbanization have whittled away the bivalves' natural, preferred substrate—dead oyster shells. To encourage new oyster colonies, the Natural Resources Group worked with Bronx River conservation groups to create an artificial reef in the estuary by stacking hundreds of plastic mesh bags full of clamshells from Long Island restaurants. "If you can get a huge colony, the water will actually be cleaned in the process of the oysters' filter-feeding," says Larson. "The oysters also provide food for both terrestrial animals and shorebirds at low tide."

Seeing Change

Despite the trash still mired in the estuary, it's "beautiful compared to how it used to be," says one Bronx River Alliance volunteer. "Over the last 10 years, we've pulled out literally tons of car parts." William Foley, a 23-year-old Bronx native and volunteer for the Parks Department's Green Apple Corps, remembers his father and older brother actually swimming in the Bronx River. "I can see a big difference here from when I was a kid," he says.

Ecologists are interested in how our ideas about nature in the past shape our expectations for nature today, and into the future. This concept is called "shifting baselines." "The idea is that most of us form our idea about what nature should be like from our experiences as children," says Sanderson. Because of ecosystem degradation, people today have a very different concept of "nature" from people a generation ago, and a generation before that.

The map work and community involvement will restore different parts of the river to different baselines, limited only by ecological reality as well as imagination. "We have to start here in our own backyard, and do restoration, even where it is most difficult," says Sanderson. "A hundred years from now, those ideas will accumulate and become a landscape that we want to live in."