3 Cape Cod towns use oysters to improve water quality

Three towns on Cape Cod are using oysters to remove nitrogen from ponds, bays and estuaries.

Mashpee Shellfish Constable Rick York launched a project roughly a decade ago to restore a former oyster fishery and to limit algae blooms caused by nitrogen discharge. By 2008, the presence of more than 500,000 oysters had led to the filtering of close to 600 pounds of nitrogen that would otherwise have contributed to algae blooms and poor water quality, according to York. One early sign that the approach was working was that Mashpee stopped seeing fish kills in its waters, he said.

The town, which has been working with the Barnstable County Cooperative Extension and Americorps Cape Cod, is seeking to reduce its total maximum daily load of nitrogen, now five metric tons per year, by 10 percent, York said.

Falmouth has launched a similar program, and Wellfleet recently won an award from the American Public Works Association for a project that includes a manmade reef initially seeded with oyster shells.

Curt Felix, vice chair of Wellfleet’s Comprehensive Wastewater Management Planning Commission, described the oyster reef, established in 2011, as a low-cost means of improving water quality.

As the first step in developing the reef, Felix said, DPW staff converted an old sander truck into a barge with an auger that could deposit oyster shells. “Cultch” – a mix of broken shells, stones and grit – was provided to create a favorable environment for oyster seedlings.

Over the past five years, Felix estimated, the population of oysters in Wellfleet Harbor has increased by more than 100 million. The reef has the added benefit of protecting Wellfleet from storm surges.

Other steps to reduce nitrogen included installing catch basins to collect stormwater that would otherwise end up in Wellfleet Harbor, Felix said.

Nurturing an oyster reef is not practical in Falmouth due to the prevalence of soft mud, according to Jerry Potamis, the town’s wastewater superintendent. So in his town the oysters are suspended in floating cages in Little Pond, a slender lake that is close to Nantucket Sound.

Potamis described the project in Falmouth as moderately successful.

The Cape Cod Commission has been leading a wastewater management planning process for the past year and a half, according to Heather McElroy, a natural resources specialist at the organization.

“We’re very supportive of the work to identify the role of oysters and other shellfish in helping to manage nitrogen in our coastal embayments,” McElroy said. “We see that as a potentially great alternative approach to managing nitrogen in the water body, as opposed to a traditional solution by putting pipes in the ground.”