Botanist and climate scientist Dorothy Peteet has been studying wetlands of various kinds for more than 40 years. Here, in the tidal wetlands of Goose Creek Marsh in the Bronx, she is investigating the amount of carbon stored in sediments. (All photos: Kevin Krajick)

NY - She's on a Mission to Plumb the Secrets of New York's Disappearing Wetlands

It was 10 o’clock on an August morning, and the sun was already broiling.

Wearing a flannel shirt and thick rubber gloves, Dorothy Peteet veered off a woodland trail in the Bronx’s Pelham Bay Park into a thick melange of brambles, fallen logs and poison ivy. About 100 feet in, she arrived at the border of a wetland ringed by a 10-foot-high wall of Phragmites—densely packed, razor-edged giant grasses. Carefully, Peteet pushed in, step by step parting the thick stalks to clear a narrow path, on the lookout for ankle-twisting watery holes. Behind her trailed three teen students.

After a few minutes, the group emerged in view of some of the most, and least, wild land in New York City. Not far off: the giant towers of Co-op City, the largest housing cooperative in the world; the traffic-choked Hutchinson River Parkway; and an embankment topped by a rumbling Amtrak train. Directly in front of them: Goose Creek Marsh at low tide, part of a 195-acre expanse of coastal wetland. Carpeted by tousle-headed wild cordgrass blowing in a slight sea breeze, it was cut by meandering creeks and little ponds, and alive with birds.

Peteet, a botanist and climate scientist, had come to measure the depth of the sediments underlying the marsh, a rare remnant of the vast wetlands that once comprised much of what is now New York City. Most have been devoured by centuries of landfilling and development, and the rest are now being slowly drowned by sea-level rise.

Wetlands are important for many reasons. Foot for foot, their thick sediments store 50 times more carbon than equivalent areas of most forests. This is true not just of tidal marshes, but inland swamps, bogs and peatlands. “Most of the carbon in a marsh is below the roots, preserved in peat,” said Peteet. “If you want to lock up carbon, instead of planting trees, we should be protecting these marshes.”

Coastal marshes also protect nearby communities from storm surge and high tides, and soak up the excess nitrogen from fertilizers and sewage coming downstream in rivers that otherwise would pollute the ocean. And, along with inland wetlands, they are home to countless rare plants, birds, animals and invertebrates.

By the 1980s, more than half the original wetlands in the contiguous United States were lost to development. The destruction has since slowed, but the nation is still losing some 80,000 acres each year. It is a global problem, and in the United States, coastal wetlands are the most endangered. The nonprofit Climate Central estimates that if business continues as usual, nearshore development and climate-driven sea-level rise could wipe out three quarters of all remaining U.S. coastal marshes by 2100. New York City has already lost around 90 percent.

Peteet, who is based at Columbia University’s Lamont-Doherty Earth Observatory and the NASA Goddard Institute for Space Studies, has been studying wetland and lake-bottom sediments for the last 40-plus years. Starting in the soggy Alaska tundra as a student in the late 1970s, she later took samples in Siberia, Kenya and the Brazilian Amazon. She went on to work on projects with two of the top climatologists of the 20th and 21st centuries: Lamont’s Wallace Broecker, credited with coining the term “global warming,” and Goddard Institute director James Hansen, who in 1988 famously warned Congress that greenhouse gases were warming the planet, and action was needed.

“Neither land nor water, maybe both, a marsh is a balancing act, a collaboration between changing elements, uncertain by its very nature,” wrote Peteet and her coauthor Daniel Wolff last year in an extended essay titled “Why a Marsh?” “It’s important to figure out how a marsh works, how it survives, why.”

Wetland sediments form as material flows into chronically flooded low-lying areas via air or water, and the remains of dead plants that have grown there build up over centuries and millennia. Coastal marshes, fed largely with mud from rivers, creeks and daily tides, can grow especially fast; in some, the first meter or so of sediment represents just the last 400 years. The deepest sediments in the New York area that Peteet has probed are in the Hudson River estuary village of Piermont, at 17 meters, or about 56 feet.

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