New York City arose in a marshy landscape amid a great tidal estuary. In 1800, there were 100 square miles of tidal wetlands in New York-New Jersey Harbor, an estuarine complex where more than half a dozen river systems meet the sea. If you're anywhere along the coast of New York City, there's a good chance you are standing on what was once wetlands.

Over the centuries, the city's marshy edges and freshwater swamps-considered no more than pestilent wastelands-were filled in and buried beneath the city's grid to make space for shipping, airports, landfills and new neighborhoods. Today, just a small fraction of the city's original wetlands, both tidal and freshwater, remain. Our last wetlands, even those preserved by the city, state, and federal governments, are under increasing threat from development, pollution, and rising sea levels due to global warming.

But renewed efforts are underway to save these vanishing ecosystems. A task force that inventoried the wetlands on city-owned land is expected to recommend transferring hundreds of acres of wetlands to the parks department. City Councilmember James Gennaro has intrduced legislation requiring the city to establish a comprehensive policy for protecting and managing the city's wetlands.

Mayor Michael Bloomberg's far-reaching plaNYC 2030 for a greener city, released on Sunday, includes a recommendation to assess the vulnerability of existing wetlands and identify additional policies to protect them, something environmental advocates say is long overdue. Recognizing the importance of wetlands in controlling flooding and pollution, the mayor also proposed expanding the city's bluebelt natural stormwater drainage system.

BENEFITS OF WETLANDS

There is no single definition for what constitutes a wetland. A wetland can be anything from a classic salt marsh to a small pool that fills only in the spring or a damp wood with tree and shrub species that like moist soil. Part of the difficulty of protecting wetlands is that many do not fit the criteria - which may include wetness, soil characteristics and vegetation, as well as size - for protection under state or federal regulations. "The vast majority of wetlands have not been officially delineated," said Bill Tai, director of the city parks department's Natural Resources Group. "But people just know a duck when they see a duck."

The city's wetlands, official or not, provide essential habitat for its surprising diversity of wildlife. "People always think of New York City as the financial capital of the world. But it is also one of the richest ecosystems in the world," said Robert Pirani, director of environmental programs at the nonprofit Regional Plan Association and a co-chair of the city's Wetlands Transfer Task Force. The marshy islands and shore of western Staten Island, for example, support large breeding colonies of herons and other waterbirds. The Hudson River's striped bass fishery depends on wetlands in the harbor. Both tidal and freshwater wetlands all over the city harbor rare remnant populations of the plants and animals that once flourished in the region.

"All the small bits of wetland that are left are really precious," Pirani said. "That's what sustains the fisheries in the harbors and the great migration of waterfowl and other birds that passes through the city."

Wetlands are valuable for many other reasons. They capture rainwater and filter out pollutants, moderating flooding and assuring that clean water goes into rivers and harbors. Tidal wetlands help buffer the coast from storms. Moist landscapes also cool the overheated city. And not least, they offer breathing space, outdoor recreation and educational opportunities to inhabitants of the concrete jungle.

In the coming decades, functioning wetlands will be essential to meeting the city's needs for clean water, open space and coastal recreation. But the city must act now, environmentalists, planners and other experts believe, to save the city's last wetlands from the myriad threats that confront them.

HOLDING OFF THE BULLDOZERS

Although significant wetlands are preserved within the city parks system as well as on state and federal lands, many coastal and freshwater wetlands throughout the city are still in private hands or on land under the jurisdiction of other agencies, and remain at great risk of development or degradation.

The Department of Parks and Recreation has a major role in protecting the city's wetlands. Of its 11,000 acres of natural areas, about 4,500 are wetlands, according to Tai. The department's Forever Wild Preserves include many significant wetlands, from the salt marshes at Idlewild Park Preserve in Queens to the kettle ponds of Blue Heron Park Preserve on Staten Island. Tai said, "People are always amazed that there are not one or two but 50 of these natural areas in the city, where you can almost forget you're in the city."

Since the passage of the Clean Water Act in 1972, federal and state regulations have slowed the filling and draining of wetlands, but there remain many huge loopholes. A 2001 Supreme Court decision weakened the federal protection of isolated wetlands, and New York State does not regulate wetlands smaller than 12.4 acres.

Last spring, Gennaro, chair of the City Council Environmental Protection committee, spearheaded the passage of a law establishing the Wetlands Transfer Task Force to inventory all wetlands on city property and determine which should be moved to the parks department, affording them greater protection. Recently, he introduced legislation to require the city "to conserve, protect, enhance, restore and expand the wetlands of New York City and to standardize the city's approach regarding wetlands management," for wetlands on both public and private property.

Conservation groups in the city continue to work toward preserving key wetlands on private property still at risk of development. In its report, An Islanded Nature, published with the New York City Audubon Society, the Trust for Public Land, which helped to save hundreds of wet acres on Staten Island in recent years, has highlighted wetland habitats on the borough's western shore in need of protection.

New York State's Open Space Conservation Plan lists several dozen city wetlands as priorities for acquisition, but, as always, there is not enough funding to purchase all of them.

PRESERVED BUT NOT ALWAYS PROTECTED

Even protected wetlands face grave threats. Wastewater discharges from sewage treatment plants and overflows of raw sewage (known as combined sewage overflows or CSOs) carry pollutants, including high concentrations of nitrogen and phosphorus that upset the nutrient balance of salt marsh ecosystems. The development of uplands and other areas surrounding wetlands increases soil erosion and contaminated runoff and diverts the flow of water that is a wetland's lifeblood. "If you pave over the soil that feeds the wetlands, the wetland is dead," said Paul Mankiewicz, an ecological engineer who heads the nonprofit Gaia Institute.

The city's remaining tidal wetlands are particularly vulnerable to sea level rise from global warming.

In Jamaica Bay, part of Gateway National Recreation Area, ecologically significant salt marshes have been mysteriously shrinking by about 40 acres a year. One of three major wetland complexes left in the New York-New Jersey Harbor, Jamaica Bay is a major stopover for birds migrating on the Atlantic Flyway and one of the best bird-watching areas in the Western Hemisphere, as well as a prime spot for fishing, boating, swimming and learning about nature. But if current trends continue, the bay's salt marsh islands will disappear within the next few decades

A task force, comprised of scientists, citizens and government agency representatives, has been working to understand the problems and propose solutions to the bay's problems. In March, the city Department of Environmental Protection released for comment its draft Jamaica Bay Watershed Protection Plan, which sets forth potential strategies, including land use changes, ecological restoration, and water quality improvement, for protecting and managing the bay's invaluable natural and recreational resources.

NATURAL STORMWATER CONTROL

About 60 percent of the city's stormwater flows into sewers together with sewage and industrial wastewater, all of which is processed at the sewage treatment plants along the coast. The wastewater treatment system is already strained. So, when a large storm hits, such as the recent nor'easter, these combined sewage overflows end up in rivers and bays, increasing bacteria counts and pollutants that harm marine life and make the water unsafe for swimming. The overflows also carry trash washed from streets into the city's water bodies.

While such overflow poses a threat to the city's tidal marshes, wetlands upstream can help provide a solution to the problem.

Like great sponges, marshes and swamps soak up rainwater and release it slowly, preventing the flooding of land, roads and buildings downstream and filtering out many contaminants. In urban areas, wetlands are especially valuable for flood control because the city's hard surfaces send greater volumes of stormwater more quickly through the streets and sewers. Wetlands are considered particularly valuable in keeping the most highly contaminated "first flush" of runoff out of the waterways.

There is a growing interest in using wetlands, along with innovative environmentally friendly techniques like green roofs and porous pavements, to control flooding at the source and reduce the sewage overflows that could become increasingly frequent with the more severe storm surges predicted for the future.

The city Department of Environmental Protection is creating a natural stormwater control and filtering system called the Bluebelt in southeastern Staten Island. In 15 watersheds covering about a third of the island, the system preserves and enhances the natural drainage corridors of marshes, ponds and streams and integrates them with conventional storm sewers. According to the environment department's web site, the bluebelt costs tens of millions of dollars less than building conventional storm sewers for the same area. The program also helps to preserve the city's last freshwater wetlands and open space for Staten Island's growing population.

The Gaia Institute, which specializes in integrating natural systems and human communities, is experimenting with building new wetlands to capture and manage stormwater. In El Jardin del Paraiso, a community garden on the Lower East Side, the institute joined with the parks and environment departments to engineer a small wetland to capture rainwater. It is now working with the company Sims Hugo Neu to create a meadow and wetland system to hold and recycle rainwater at its metal recycling facility on the Bronx River.

Engineers at the Department of Environmental Preservation question whether the restoration and creation of wetlands and other natural infrastructure can make a measurable difference to the sewage overflow problem in densely developed areas of the city. But the department has publicly committed itself to coming up with pilot projects that look at the use of wetlands for stormwater management.

TASK FORCE RECOMMENDATIONS

The Wetlands Transfer Task Force looked at 2,000 wetland parcels on city owned land. About a thousand of these were already under the jurisdiction of the parks department. As for the rest, Pirani said that the panel will recommend that several hundred acres be transferred either to parks or the Department of Environmental Protection for its Bluebelt program.

These include a number of wetlands around Jamaica Bay, as well as areas elsewhere in the city that have value as wildlife habitat, for stormwater management or are in a part of the city with few other green spaces.

The release of the task force's final report has been delayed, however, pending a study by the Economic Development Corporation on economic issues around the wetland that led to the group's creation in the first place - Arlington Marsh on the northwestern shore of Staten Island.

The marsh is adjacent to the Howland Hook Marine Terminal, a large container port leased from the city by the Port Authority. The site in question, one of the last remnants of the salt marshes that once encircled Staten Island, has a rich variety of flora and fauna within a very small area. The city wants the land for possible future expansion of the port. The task force members representing planning and environmental groups say that the wetland should become a park because there are other sites for the terminal but only one marsh.

The panel also found that the issues affecting wetlands go beyond whether or not particular parcels should be protected as parks. A whole range of policies involving almost all city agencies could work to the benefit - or detriment - of wetlands. In addition, any strategy to protect these areas must also consider funding. Such an overall management strategy is essential, Pirani said, because "in a place as urbanized as New York City, if you ignore wetlands, they won't be there forever."

Anne Schwartz is the author of "Rescuing Wetlands Close to Home: Ten Stories of New England Landowners," published in September 2006 by the Trust for Public Land.