TRURO — The neat stacks of concrete pipes lined up along Route 6A in North Truro are not a public art project. They are being installed underground as part of phase two of a multi-million-dollar ecological repair effort. The pipes are part of a new concrete culvert that will bring an infusion of seawater and tidal flow from Cape Cod Bay into East Harbor, also known as Pilgrim Lake.
The benefits of increased tidal flow to the lagoon have been extensively documented, and scientists hope to see further improvements with the newly replaced culvert.
The reasons for all this plumbing lie deep in the history of Cape Cod. East Harbor was at one time an anchorage so secure and protected that the Mayflower took advantage of it in 1620.
When English settlers logged the surrounding forests, the thin layers of topsoil were destroyed by winter winds, exposing the sand below. Windblown sand settled in East Harbor, filling in its deep waters until it became commercially useless. In 1868, its northern outlet to Cape Cod Bay was filled in to help support the newly laid railroad tracks connecting Provincetown to the rest of the Cape, Boston, and New York.
That barrier of land between East Harbor and Cape Cod Bay is what created Pilgrim Lake, isolating it from the ocean and regular flows of salt water. The 346-acre lagoon became anoxic, or oxygen-deprived. The lake sometimes stank, and it sat stagnant for decades.
A fish kill in 2001 led to the opening of the first culvert connecting the lagoon to Cape Cod Bay. Restoring saltwater flow into the lake helped re-oxygenate the water, and dozens of saltwater species have since moved in.
But sinkholes under the culvert created partial blockages in 2016, and the town of Truro voted in 2017 for a two-phase, $3.7-million culvert replacement project. Phase one repaired the seaward section of pipe, from Shore Road to Cape Cod Bay, in 2019. The section from Shore Road to Route 6 is being replaced now, and should take about 12 weeks and cost $1.6 million, according to Truro DPW Director Jarrod Cabral.
The National Park Service is collaborating with the town of Truro to monitor the health of East Harbor and the species that live there.
Sophia Fox, an aquatic ecologist with the Cape Cod National Seashore, said that many marine species thrive in Pilgrim Lake. She said every type of shellfish native to the Outer Cape can be found in the lagoon, including mussels, oysters, scallops, clams, razor clams, softshell crab, and even cockles.
There are also flounder and striped bass, which Fox encountered when she was scuba diving in the lake last year. “It was pretty startling,” Fox said. “I was swimming along and this school of striped bass came right toward me.”
The fish were about 15 inches long, so around five to seven years old, said Fox. There are also mummychugs, stickleback, pipefish, eel, and killifish in the lake, and many different types of gulls, geese, ducks, kingfishers, and other seabirds.
There are even river otters in East Harbor, and the horseshoe crab population has been particularly robust, Fox said.
While many marine species are thriving, some are not, Fox said. The shallowness of the lake could be a reason why some species have disappeared or decreased in number. Pilgrim Lake is now only six feet deep at its deepest point, Fox said. Shallow bodies of water warm quickly and don’t provide the cooler, deeper refuges that some species need to survive.
One disappointing die-off has been the eelgrass planted in 2011. Fox said she noticed last year that it had died, and since the vegetation wasn’t being regularly monitored, she isn’t sure exactly when it occurred. She plans to get out on Pilgrim Lake in April to look for any signs of the native underwater plant.
“We’ll check it out when the grow season starts again,” Fox said. “Maybe they didn’t die all the way to their roots.”
Eelgrass is a type of seagrass native to the Atlantic coast and is key to a thriving saltwater habitat and a bellwether of health, Fox said. It provides necessary nursery habitat for a number of saltwater species. The underwater grass also filters and clarifies the water.
“That’s one of the most prized habitats of our region,” Fox said of the eelgrass, “because so many species are attracted to it and want to live in it. It also sequesters a lot of carbon. Seagrass beds globally actually sequester more carbon than rainforest, so they’re pretty important.”
The population of shellfish changes annually, which is another Pilgrim Lake puzzle, said Owen Nichols, director of marine fisheries research at the Center for Coastal Studies in Provincetown.
“Some years, the shellfish are very abundant and other years they’re not, so we’re really trying to get a handle on why there are changes and why the shellfish community seems so variable,” he said. “There’s a variety of different animals that can be predating on the shellfish, so we’d like to understand that better.”
Nichols grew up on the Outer Cape and sang Pilgrim Lake’s praises.
“I do a lot of plankton sampling right there, and it’s just such a cool spot,” he said. “There are kingfishers that swoop down, and it’s very serene. I’m there early in the morning, or late at night sometimes. It’s one of my favorite places to work.”
The culvert project should be completed by June, and scientists will be studying Pilgrim Lake this spring and summer, anxious to see the effects of improved tidal flow and to better understand some of the riddles the lagoon still poses.
“It’s exciting to be part of these projects from start to finish, because they really take a decade to complete,” Fox said. So far, opening the tidal flow to the lake has “really been extraordinarily successful.”
