With salt marshes dying, we're in for trouble

Coastal-zone experts have been scurrying faster than shallow-water crabs lately. Long-term weather forecasters are predicting hurricanes, causing south-of-Boston coastal communities to ponder their sea walls, piers, culverts, and similar features, many of them old and crumbling, and prompting insurance companies to sharpen pencils. And now the Coastal Hazards Commission suddenly faces a nasty new and possibly intractable crisis involving changes happening so fast its data collection may prove useless: salt-marsh sudden dieback syndrome, which looms as far worse than an ecological catastrophe for fish, birds, and other wildlife. Dying and dead marshes will mean a new coastal topography, especially after a hurricane strike or winter gale.

Recent news reports have emphasized the ecological crisis evident in salt marshes turning brown as marsh plants die. Salt marshes are perhaps the richest ecosystems in the world. They are home to countless varieties of wildlife, especially to varieties of birds. Their grasses and other plants are part of a ecosystem of crabs and other animals that in the long run furnish the food for ocean fish and larger creatures higher on the food chain. Since the 1880s, scientists have recognized what fishermen have always known: Salt marshes are the backbone of the New England's offshore ocean fishery.

Sport fishermen prize the striped bass and other fish that course along salt-marsh creeks, feeding at high tide on the tiny animals of the shallows. Water fowl hunters operate in the marshes in autumn, shooting ducks, geese, and other game birds in habitats often protected and maintained through funds raised by hunting license fees and duck stamps. Any thoughtful observer who glances at fishermen and hunters off in the distance realizes that marshes support animals large enough to feed humans.

Sudden dieback is heart-wrenching to see. Scientists are unsure why this is occurring. All the plants, especially the tall, thin spartina grasses, lie brown and dead atop brown silt and brown peat. Even more rugged invasive plants, especially the alien phragmites marsh-lovers loathe because it forces out native Massachusetts plants and proves a poor habitat for birds, dies. Observers cringe at the color change. The soft brown winter marsh, the chartreuse spring marsh, and the deep green marsh of summer and fall all become a chocolate brown mess. Close inspection shows a thin layer of silt mixed among the dead plants, or crumbling, sponge-like peat where dead plants and silt have washed away.

But many people forget that salt marshes stabilize the whole network of coastal defenses. All too often, even specialists see marshes as ecological treasures and forget their role in backing barrier beaches, culverts, bridges, and sea walls. Boaters, kayakers, marina owners, commercial fishermen, and others who cruise inland waters forget that marshes trap tide-driven silt. Only in vague ways do they understand the marshes are buffers that stop gale and hurricane damage.

Marshes indeed keep great barrier beaches in place, and they slow freshwater floods crashing into the sea following heavy rains. Since about 1900, engineers have understood the role of marshes and planned accordingly. But marsh dieback changes all the rules almost instantly.

Along the Quincy shore, especially around Squantum, along Route 3A in Hingham, particularly just north of the harbor, in the salt marshes of Cohasset, and the whole mouth of the North River between Scituate and Marshfield are examples of what is best seen in Duxbury and Plymouth, on the bay side of the great barrier beaches. Over centuries, but chiefly since the 1920s, summer vacationers and then year-round residents have built on land shouldered by salt marshes. Local and state highway departments have built roads to serve the dwellings and the businesses that followed them. An improved gravel road even runs along the bay side of Duxbury beach. But just inland from the beaches so often graced with large, expensive houses, lie salt marshes. Children sometimes sneer at the salt marsh on the opposite side of Duxbury beach. Dunes keep a beach relatively stable, but it is the backside marshes that children find yucky that anchor the whole beach.

Dying salt marshes first release silt and plant material into salt creeks and estuaries. The Fore River excluded, this region lacks deep-water harbors and estuaries. At Green Harbor and the entrance to the South River in Marshfield, careful boaters see what characterizes many other inlets. Sand bars and mud bars inhibit navigation. Volunteer environmental organizations champion kayaking and canoeing, often in dangerous waters, in part because they see sedimentation as natural. But the channels lacing the South Shore are mostly artificial, dredged decades ago and silting in ever so slowly. Now the organizations and the public face serious choices.

As salt marshes die, they release their top coating of silt, which is usually about 6 to 12 inches thick. The silt moves with the tides, usually becoming a mud bank that deflects currents, produces other banks, and after a bad storm can wholly reshape or choke a small estuary or harbor. Choked estuaries and harbors mean ruined marinas and crippled shoreside industries. Dredging no longer works, since without marshes, adjacent nonrocky upland simply erodes with the tides.

No one fondly remembers Bird Island flats, the muddy bars made into Logan Airport with fill barged from Scituate. Mud flats provide clams, but they are not picturesque, and they do little to restrain hurricanes. Imagining the South Shore without healthy marshes means imagining hurricanes driving seas deep into Quincy and Milton and across Route 3A in Hingham. It means visualizing waves eliminating Peggotty Beach in Scituate and thrusting across Front Street at Satuit Brook and smashing behind Third Cliff into the North River. It means imagining the breaching or complete destruction of Duxbury Beach and the inland side of the Gurnet at Plymouth, the transformation of Duxbury and Plymouth bays into open sea, and the wholesale transformation of the lower Plymouth coast and the Wareham and Mattapoisett shores.

In 1980, Rutherford Platt and George McMullen, two University of Massachusetts experts, published a report on the Blizzard of 1978 coastal flooding. It still makes scary reading. Analyzing hurricane or winter gale flooding in area towns bereft of salt marshes suggests that whole chunks of the coast will move inland, perhaps putting sleek sandy beaches where people now live. But it suggests, too, that many remaining expensive homes would overlook mud flats that would scarcely slow subsequent hurricanes, that estuaries and salt creeks would be truncated or smothered in sandbars covered with shallow water only at high tide, and that the Dutch are right to design everything alongshore for 500-year storms.

Norwell resident John Stilgoe is Orchard Professor in the History of Landscape at Harvard University.