First Responders to the Nitrogen Crisis
Decades of nitrogen loading create the perfect conditions for algae to proliferate: thick green mats that float on the surface, feeding on nitrates and sucking up oxygen in the water, a process known as eutrophication. When the algae eventually die, they fade to brown, releasing a nasty sulfur smell and coating the sea floor with gelatinous muck.
Some of the biggest casualties of the nitrogen imbalance are the shellfish that make Cape Cod famous. The lush eel grass beds that once sheltered bay scallops are distant memories. It’s rare to find water clear enough to spot littleneck airholes in the sand—or sandy bottom at all.
Though it’s still possible to fill up a basket of steamers in many of the Cape’s coastal ponds, odds are they were seeded by the local shellfish warden. Overfishing, development and disease have also put a dent in shellfish populations, but declining water quality has made it hard for the creatures to bounce back.
But strangely enough, shellfish are being hailed as a potential savior of the bays. As filter feeders, oysters and quahogs can process 15 to 25 gallons of water a day (up to 50 gallons in the warmer months), vacuuming up microscopic algae that thrive in nitrogen-rich waters.
This voracious filtering capacity has attracted scientists’ attention from Chesapeake Bay to Cape Cod, spawning aquaculture projects in its wake. The Mashpee Wampanoag Tribe were among the first to capitalize on the research in 2009, pairing an extensive water quality monitoring program with a 4.6-acre oyster farm in Popponesset Bay. Borrowing its trade name from the word Wampanoag, or “people of the first light,” First Light Oysters have been sold from Duxbury to New York City since 2010.
Walking along the beach where she tends her oyster cages, farm manager Kris Clark picks up a clump of hairy-looking seaweed.
“The oysters feed on the microscopic version, so hopefully that’ll help get rid of the bigger seaweed,” Clark says. “And then we eat the oysters, so it’s one way of harvesting the nitrogen in Popponesset Bay.”
Until recently, scientists weren’t quite sure how—or how much—nitrogen was taken up by local shellfish. But a study released in January by Woods Hole Sea Grant and the Cape Cod Cooperative Extension found that quahogs and oysters each contain about a quarter gram of nitrogen in their tissue and shell. If harvested, that could remove thousands of pounds—if not tons—of nitrogen from Cape Cod bays. Along with other adaptive management strategies, aquaculture features prominently in the Cape Cod Commission’s new Water Quality Management Plan, a tool designed to help towns meet strict nitrogen-loading limits set by the state.
Though none of the proposed solutions are cheap, aquaculture is proving more palatable to voters than the bitter pill that is traditional wastewater treatment. Not only are oyster farms profitable, they create self-sustaining jobs and a local source of food.
Shellfish cultivation is on the rise, particularly for oysters. Of the 360 aquaculture licenses issued in Massachusetts in 2013, over 250 of those were on the Cape. According to the Department of Marine Fisheries, farmed oysters brought in close to $12 million statewide in 2013, a doubling in the past five years.
“It’s a huge economic resource. You are feeding people. When you look at the amount of shellfish seafood that we import, we could be growing a lot of our own,” says Diane Murphy, one of the authors of the Woods Hole Sea Grant/Cape Cod Cooperative Extension study. “And you’re also helping to prune back that excess production—removing nitrogen as you’re harvesting.”
For the Mashpee tribe, the economic potential is secondary to the ecological benefits. To help understand the tribe’s goals, I joined Quan Tobey, director of natural resources for the Wampanoag Tribe, his assistant director, George “Chuckie” Green, and Rick York, the Mashpee shellfish constable, on a tour of Mashpee River, one of the most impaired waterways on the Cape.
“Aquaculture is something we’ve traditionally, historically done here,” Tobey says as we pass Daniel’s Island, where Wampanoag oyster farmer Horatio Amos once shucked oysters, and who—legend has it—paved Red Brook Road with oyster shells.
“The natural, wild resource isn’t the same. But this is what we need to do to restore it, and our cultural traditions,” Tobey says.
Working together, the tribe and town of Mashpee are attempting to do just that. Around the bend from the First Light Oyster farm, York is growing half a million oysters in the Mashpee River. He estimates that’s equivalent to removing five percent of the nitrogen polluting the river—an amount too small to meet the state mandate, but enough to prevent a repeat of the fish kill that made headlines in 2005.
Theoretically, York says, oysters could filter out the 12 tons of nitrogen Mashpee is required to remove from the Popponesset Bay system. That would mean expanding to ten million oysters—about ten times what is in the bay right now. “There were that many oysters here before. We just have to get them back,” says York.
But despite the potential, York and Tobey are quick to warn that oysters are not a silver bullet for cleaning up all the nitrogen from the Cape’s waterways. “I look at oysters as first responders,” says York. “But there’s some places where shellfish couldn’t, wouldn’t work. They’d have to clean up the sources first.”
And that won’t happen overnight. As Green points out, even if all of the Cape was sewered tomorrow, the nitrogen that’s already in the groundwater would take decades to cycle through the estuaries. But he remains hopeful that the bay could turn around sooner rather than later.
“This is going to be a constant battle for quite a long time,” he says as we stop to take a water sample in an undeveloped area at the head of the river. “Aquaculture is just one bit of ammunition in the fight,” says Tobey. “If we get to that [nitrogen loading] limit, it’s not like, ‘OK, full bore with development again, let’s build houses along here.’”
Tobey’s words resonate as we pass a seemingly endless line of waterfront houses where shellfish used to thrive. But Tobey is too young to remember those days—for that, he looks to Green.
“As a child, oysters were almost a foot thick on the bottom of the bay,” Green recalls “The bay was loaded with shellfish. You could make a living on shellfish. You could live on shellfish, and that’s what we did. We didn’t have a grocery store.”
Green can remember the year it all started to change: 1964, when Mashpee passed a Special Permit that allowed development outside of the town’s zoning laws. In the next 50 years, Mashpee’s population skyrocketed, from a tight-knit community of 700 to a bustling town of 15,000.
“We developed so fast we didn’t think of the consequences. We weren’t ready as a people, as a community, as a town, to pay for what we were doing to the environment that we wanted to live in,” Green says. “All the impact is that I can’t come down here and just dig a bucket of clams.”
As Clark is the first to point out, running an oyster farm is a whole lot harder than digging a bucket of clams. Just like every farmer, she has to balance the challenges of Mother Nature with the demands of the customer—and state regulators.
“Farming is part science, part art, but mostly luck,” says Clark, who never stops moving as we chat during a morning low tide, pulling trays up to shore, loading oysters into new ones, and removing the crabs, worms and muck that creep into the cages over time. Rain or shine, in the snow and biting wind, Clark and her assistant Tony Perry brave the elements to grow the two-millimeter oyster seed to market size.
Oysters are tastiest in the late fall, when they bulk up on fats—and take up the most nitrogen, says Clark. Like wine grapes, oysters derive flavor from their growing medium. Due to the conditions in Popponesset Bay, First Lights have a mild salinity, with a creamy, balanced finish.
“We can’t do anything about the taste. It’s a function of where they’re grown,” says Clark, shoveling a load of market-size oysters from a tray to an orange basket. “Each grower’s oysters are little different. Just like wines, with subtle variations on the taste.”
First Light Oysters are available at the Island Creek Oyster Bar in Boston and at the Island Creek company store in Duxbury.
See how oysters filter algae, and find out more in Saving Paradise: Water for Oysters, a video produced by the Association to Preserve Cape Cod and UnderCurrent Productions.
