Rising sea levels are swamping coastal wetlands at an alarming rate, threatening migratory birds and some of the most valuable seafood species, a new federal study shows.

NOAA Fisheries and the U.S. Fish and Wildlife Service, with funding from the U.S. Environmental Protection Agency, issued a report that also found losses tied to traditional problems, such as urban and rural development, agriculture and forestry practices. The study linked the loss to population pressures as Americans’ move to coastal areas, increasing the density from just more than 300 people per square mile in 1970 to more than 450 people today.

Loss of coastal wetlands has accelerated, it found. The National Oceanic and Atmospheric Administration looked at wetlands losses along the Atlantic, Gulf, Pacific and Great Lakes coasts from 2004 to 2009 and found 80,160 acres were lost each year.

The losses were only 60,000 acres per year when the first such study was done, covering the years 1998 to 2004. This has ramifications for the commercial and recreational fishing industries, as nearly 80 percent of the species they target rely on coastal wetlands at some point in their life cycle.

“The three most valuable species that depend on habitats supported by our wetlands — crab, shrimp and lobster — had a combined value of $1.6 million in 2012. The disappearance of this habitat could be detrimental to our nation’s seafood supply,” said Mark Schaefer, NOAA’s assistant secretary for conservation and management.

Another concern is migratory birds. Fish and Wildlife Service Director Dan Ashe noted that coastal wetlands support 75 percent of migratory birds, and almost half of the federally listed threatened and endangered species.

Big losses

Researchers were expecting big losses on the Gulf coast from the impact of recent hurricanes Rita and Katrina swamping saltwater wetlands, and sinking land from oil removals in that region, but they were surprised at losses in other areas including the Delaware Bay.

“We knew Louisiana was losing 14,000 to 20,000 acres a year and thought maybe we’d get double that in the rest of the U.S.,” said Susan-Marie Stedman, a fisheries biologist with NOAA Fisheries.

“I’m alarmed by what we’re seeing. It’s a lot of wetlands to be losing on top of what we’ve already lost,” Stedman said.

The study found thousands of acres of estuarine salt marsh on the Delaware Bay have been lost from erosion and tidal inundation. This has been blamed on rising sea levels, changing ocean currents driven by the Gulf Stream that are pushing more water toward shore in the Mid-Atlantic region, and a land mass south of the last glaciation that is still sinking.

“The earth’s crust under the Delaware Bay is sinking at a rate faster than the land around it, and sea level is rising faster there, making it real challenging for the marshes. They need to build themselves up and move inland. As sea level rises the key is wetlands migration,” Stedman said.

Putting structures up to stop the sea, such as bulkheads or revetments, does not allow the wetlands to migrate. About 43 percent of New Jersey’s developed shoreline already has been armored in such a way, but experts say the migration of wetlands depends on having an open area to move to with no development that must be protected.

It also depends on sediment transport to the marshes. New Jersey is considering using materials from dredging projects to help the marshes overcome the higher sea levels.

“It used to be we considered dredged material a waste product, but now it could be a resource,” said Danielle Kreiger, the science director at the Partnership for the Delaware Estuary, a group dedicated to protecting the region’s watershed.

Sediment starvation is listed as one reason for the Delaware Bay’s problems. Sediments historically flowed here from rivers, melting glaciers and processes in the bay itself.

“There’s no new sediment,” Stedman said.

The numbers

From 2004 to 2009, there were 360,723 acres of coastal wetlands lost in the lower 48 states, or 0.9 percent of the total, which leaves more than 41 million acres.

The biggest losses were in the Gulf, where 257,150 acres disappeared, most due to tidal inundation. Wetlands filled in for development are lost as wildlife habitat. Wetlands inundated by higher sea levels are no longer wetlands; once they are covered with 6 feet of water they are considered “deep-water habitat.” This land still serves a variety of fish and migratory birds but is not as economically valuable as wetlands washed periodically by the tides.

The Atlantic coast lost 111,960 acres. The Pacific lost 5,220 acres. The Great Lakes gained 13,610 acres, due in part to wetlands restoration programs and declining water levels.

The research discovered the losses by looking at digital high-resolution images and then doing verification on the ground in some areas.

Kreiger said the study confirms numbers her group has found when it periodically reports on the state of the Delaware Estuary. Kreiger said a report from 1996 to 2006 found wetlands losses of more than 3,000 acres, or 0.92 acres per day in the estuary. She believes it has escalated and is now more than 1 acre per day.

Kreiger is concerned as some experts are warning of a sea-level rise of one meter by the year 2100. A one-meter rise would put more than 1 million acres of wetlands in the Mid-Atlantic at risk of inundation, including 352,619 acres in New Jersey, according to an EPA study.

Kreiger adds 0.15 meters to the expected rise due to land subsidence and 0.15 to 0.25 meters due to ocean currents. This is an increase of at least 1.3 meters by 2100.

Matter of millimeters

Kreiger said sea level is rising by at least 4 millimeters per year now and could reach 10 millimeters by the middle of the century.

“We’re seeing erosion and drowning wetlands at 4 millimeters a year. What will happen at 5, 6 or 7? Once you get to 10 millimeters a year, you’ll probably only have wetlands existing next to rivers,” Kreiger said.

Another problem is the land subsidence. The last glacier stopped in northern New Jersey more than 10,000 years ago. The land under that ice is now rising back up after being pushed down by the weight of the glacier. Land to the south is sinking.

“It’s like a seesaw and we’re at the other end of the seesaw,” Kreiger said.

A study of Mid-Atlantic Region by NOAA showed about 40,000 acres of wetlands were lost from 1996 to 2006 with 27 percent of this being converted to open water. Agriculture, most in the Chesapeake Bay region, took 48 percent of the wetlands while 15 percent was lost to development. The study found 53 percent of the sea-level rise in the lower Chesapeake Bay was due to land subsidence. Dredging projects also were listed as a threat as the material is often stockpiled in the marshes.

There are a number of ways to help give wetlands room to migrate, such as land acquisition, rolling easements, density restrictions and setbacks. Most are not feasible in fully developed areas, but the bayshore is sparsely developed and has valuable fisheries, such as oysters and finfish, and sports migratory waterfowl and the world’s largest concentration of horseshoe crabs.

The losses have other ramifications, such as reducing protection of coastal communities from storms, contaminating aquifers and reducing outdoor recreation.

Department of Interior Secretary Sally Jewell said the study showed wetlands four times the size of Miami are being destroyed every year, so much more needs to be done.

“Wetlands are important to our nation’s heritage, economy and wildlife, especially when it comes to our coastal communities,” said Jewell.

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