In Truro, a dying lake now overflows with life

TRURO -- The salty tide once again pours into Pilgrim Lake, choking the invasive freshwater reeds that long ago replaced the shallow, marshy pond's natural inhabitants. The same briny flow has fueled the recovery of saltwater species now repopulating the lake for the first time in more than 130 years.

Just two years after ecologists began what they call the largest New England coastal wetlands restoration project ever, the once-moribund lake now brims with life. A burgeoning field of mollusks -- mussels, clams, and quahogs -- have returned to their ancestral home along the slender strip of dunes and shoreline that connects Provincetown to the rest of Cape Cod.

Scientists hope their success at Pilgrim Lake will provide a springboard for an ambitious effort to restore nearly all the Outer Cape's coastal marshes. Mike Murray, acting superintendent of the Cape Cod National Seashore, which is restoring Pilgrim Lake, hailed the return of the mollusks as a watershed achievement that showcases the myriad benefits of reuniting coastal marshes with the sea.

All it took was inviting the tide in and letting nature run its course, Murray said. In 2002, ecologists opened a small tidal culvert to funnel saltwater back into the choked, oxygen-poor marsh.

"It's like a miracle cure," he said. "In ecological terms, you're usually talking decades to restore damaged ecosystems. This happened almost overnight."

The effort aims to reverse an age-old trend. For generations, man has drained, filled, and built over coastal wetlands. But a growing recognition of estuaries' vast environmental value has spurred a sharper commitment to restore them.

Such efforts have accelerated since the passage of a 2000 federal law calling for the restoration of 1 million acres of wetlands by 2010, said Steve Emmett-Mattox, vice president of Restore America's Estuaries, a national nonprofit group.

Pilgrim Lake used to be called East Harbor, back when it was connected to Cape Cod Bay by a 1,000-foot inlet. But a dike built in 1868 to clear a path for a railroad, where Route 6 now lies, sealed the harbor from the sea. Gradually, the salt marsh's waters turned fresh.

When that happens, invasive plant species crowd out native vegetation, stifling marine life, said Steve Block, a habitat restoration specialist with the National Oceanic and Atmospheric Administration's fisheries center in Gloucester.

At Pilgrim Lake, 40,000 herring died from chronic oxygen depletion in 2001 before scientists opened the culvert and let the sea in. Now, emerald-green eelgrass grows on the marsh floor, and little silver-sided fish called mummichogs dart in the floodplain's salty shallows. Black ducks land on patches of widgeon grass.

Covering more than 700 acres, Pilgrim Lake accounts for 250 more acres than the total swath of wetlands restored in Massachusetts, said Tim Smith, a wetlands scientist for the Massachusetts Office of Coastal Zone Management.

"In the context of coastal wetlands restoration projects. . .it's unprecedented," Smith said.

Ecologists hope the Pilgrim Lake project serves as a prototype. A similar plan to channel more saltwater into Provincetown's Hatches Harbor has yielded steady, if less dramatic, environmental progress. Seashore scientists are now studying ways to conduct a similar project in Wellfleet's Herring River, the outer Cape's largest estuary, by removing tidal barriers.

Last week at Pilgrim Lake, John Portnoy, a seashore ecologist leading the restoration, proudly pointed to a recently hatched bed of blue mussels resting on a sand bar near the culvert. They are the product of an ecological ripple effect, he said.

The wetlands' salinity has made the soil far healthier and nutrient-rich. That has spread benefits all along the food chain -- from microorganisms to submerged plants to fish to waterfowl. As a result, the entire ecosystem improves. Meanwhile, the nonnative species that were wreaking havoc with the marsh's habitat are dying, unable to survive in saltwater.

"That's how ecology works," Portnoy said. "You change one thing, and everything changes."

Scientists are also studying possible negative consequences of restoring salt marshes. "It should be looked at carefully," said Bill Walton, a fisheries and aquacultures specialist affiliated with the Woods Hole Oceanographic Institution. "The reality is all ecosystems may have some value. If we're going to change it, we should know what we're changing."

Some residents in Wellfleet are concerned that once the Herring River is reconnected to tidal patterns, storm tides will flood their property. Fishermen in the town say restoring the river's natural ecosystem would help water life flourish.

"You open it up like it used to be, like the way nature intended, and it can only help," said Irving Puffer, who has been a Wellfleet shell fisherman for 25 years.

Parker Small Jr., a member of Truro's shellfish advisory committee, said restoring salt marshes will replenish depleted stocks. As a boy growing up in the 1950s, he could dig up a bushel of clams snorkeling for half an hour in the bay. Now he is lucky to see one clam an hour, he said.

Scientists see the restoration project as a way to make things right in a place they insist on calling by its old name, East Harbor.

"I know development had to take place," said Gregg Moore, a scientist with the Center for Coastal Studies in Provincetown, "but it's nice to put things back."

Peter Schworm can be reached at schworm@globe.com.