Climate change poses rising threat to Chesapeake Bay marshland

[Donna]

CAMBRIDGE — Tens of thousands of migrating waterfowl, one of the nation's largest populations of breeding bald eagles and the endangered Delmarva fox squirrel all call Cambridge's Blackwater National Wildlife Refuge home.

And all are vulnerable to the rising sea levels that threaten coastal marshland.

The Chesapeake Bay is experiencing sea level rise at a rate twice the global average, and the thin ribbons of marshes and wetlands that form along coastlines--Blackwater, Smith Island, Assateague Island--will be the first to be flooded with rising water.

Flooded marshland means the loss of land that filters nutrients and pollutants from entering the water and acts as a barrier to offshore storm surges. It also means the destruction of vital habitat for the wildlife that forms the backbone of Maryland's seafood industry and tourism economy.

Since the 1930s, Blackwater has lost 5,000 acres of marshland, said Dixie Birch, supervisory biologist at the refuge. Blackwater contains one-third of Maryland's tidal wetlands, which are disappearing because of factors like climate change, saltwater intrusion and animals like the nonnative nutria and resident Canada geese that consume loads of vegetation.

A report from the College of William and Mary's Center for Conservation Biology predicts that sea level rise will have catastrophic consequences for marsh birds, causing an almost 80 percent population decline in species like the clapper rail, seaside sparrow and marsh wren.

The problems that marshland loss can cause for fisheries are probably even more extreme than those it causes for marsh birds, said Mike Wilson, a research biologist at the center who headed the study. Fisheries rely on marshlands as both a spawning ground and a nursery for juvenile fish.

Although the leading cause of sea level rise in this region is global warming, the state's marshes are undergoing "a two-pronged attack," Wilson said.

The sea is rising, but the land is also sinking due to the compaction of the earth's crust, said Wilson. Some also attribute such land subsidence to our withdrawal of water from underground aquifers, citing their creation of a vacuum that allows marshes to sink into "areas that were once filled with water and are now empty," Wilson said.

"Some wetlands can keep up with sea level rise, and have kept up with sea-level rise," said Andrew Baldwin, associate professor at the University of Maryland's Department of Environmental Science and Technology.

"The question is, will coastal wetlands keep up with this newer, faster rate of sea level rise? And where are those wetlands?" Baldwin said.

Not in Maryland. Although marshlands have the potential to migrate inland, their movement depends upon the presence of forgiving topography, and the elevated part of the (Chesapeake) bay's shoreline "is just a little bit too much above sea level for these marshes to really go anywhere," Wilson said.

"There gets to be a point where the elevation is so high that you won't have a marsh form. It'll just stay dry. So what you see is these marshes being squeezed out of existence," Wilson said.

Even if marshes were to migrate, the new wetlands that would develop over flooded land "would not offset the loss of existing wetlands," concluded the Climate Action Plan released in August 2008 by the Maryland Commission on Climate Change.

Another obstacle to marshland migration has appeared along coastlines in recent decades--shoreline armaments, or structural methods of shoreline erosion control.

The state's shorelines are "becoming armored at a relatively high rate" with structures like bulkheads, retaining walls, stone revetments and riprap, Wilson said.

"These seawalls ... prevent marshes from being able to move any further inland," he said.

In October 2008, the state implemented the Living Shoreline Protection Act, requiring landowners to install living shorelines rather than other methods of erosion control, unless another method is proven more appropriate.

Living shorelines, built by placing plants, stone, sand and other material along coastlines, mimic marshlands and work "in concert with nature to provide that interface between land and water where both can benefit," said Jordan Loran, director of the Department of Natural Resources' office of Engineering and Construction.

Living shorelines are "becoming more and more the matter of course, as the technology develops and the importance of wetlands becomes more and more apparent," Loran said.

Marshland restoration in Blackwater has stalled due to a lack of funding.

During the 1980s, the refuge restored 12 acres. In 2003, eight more were restored. The recent postponement of a partnership that would have funded the restoration of thousands of acres was "a big disappointment for us," Birch said.

The refuge is now restoring Barbados Island, which sits at the center of Blackwater and is losing .8 acres of land each day.

Senators Benjamin L. Cardin and Barbara A. Mikulski, Democrats, announced Friday the passage of a bill containing $2 million in funding to acquire more land for Blackwater.

Marshland loss will prove to be a difficult problem to solve.

"Climate change is a difficult [problem] because you can't really fight rising temperatures that accompany rising seas," Wilson said.

[Dot_Forrester]

  Donna, that was interesting, very depressing, and definitely scary. 

Dot in PA