Pleasant Bay Watershed Cleanup On Track : Bay Towns Make Headway Reducing Nitrogen

By: Alan Pollock

Topics: Groundwater protection , Pleasant Bay

A speedboat makes its way past Strong Island toward the North Cut. The new inlet greatly improved tidal flushing in Pleasant Bay, but can’t be counted on as a permanent benefit, officials say. ALAN POLLOCK PHOTO

CHATHAM — In the first three years that the towns of Orleans, Chatham, Harwich and Brewster have operated under a regional watershed permit, they’ve achieved around 75 percent of their five-year goal for controlling nutrient pollution entering Pleasant Bay. That’s the news from the Pleasant Bay Alliance, which issued its annual report to the member towns recently.

“The good news is that things are pretty much on track,” Alliance Coordinator Carole Ridley told the Chatham select board last week.

The regional permit requires the four towns around Pleasant Bay to remove a total of 17,717 kilograms of nitrogen from the entire watershed each year for the next 20 years. Brewster is tasked with removing 13 percent of that amount, Chatham has responsibility for 23 percent, Harwich has 25 percent, and Orleans must remove 39 percent, or 6,980 kg per year. Mostly from septic systems, the nitrogen makes its way through the groundwater to the bay, causing algae blooms that can lead to the loss of eelgrass beds, shellfish and other marine life.

The permit sets five-year goals for the towns, and by the fifth year, the four towns must have removed 4,914 kg of nitrogen. By the end of this fiscal year, year three under the permit, they will already have removed 3,566 kg.

Those nitrogen removal targets are based on data from 2006, and are being updated with new information. Part of what’s changed is the tidal flushing in and out of Pleasant Bay, Ridley said.

“New hydrodynamics...take into account the changes in the inlet configuration that have happened since 2006, which have been significant,” she said. The North Cut opposite Minister’s Point provides much more rapid water exchange than in the past.

“I boat there all the time. It’s phenomenal how clear, a times, that water is,” Chatham select board member Jeffrey Dykens said. The new inlet is clearly beneficial to water quality in the bay, he said. “Never mind Chatham. It’s got to be helping Harwich, Brewster and Orleans as well.”

Ridley acknowledged the improvement the new inlet has brought, but said it’s not a permanent benefit. As the barrier beach migrates, the inlet will move southward, reducing the tidal exchange in the decades ahead before a new inlet forms to the north, repeating the cycle. While the bay is currently enjoying robust flushing, “we can’t count on that forever,” Ridley said.

Better water flow under Route 28 at Muddy Creek and Tar Kiln Creek have also improved flushing to those sub-embayments, which the new numbers must account for. At Muddy Creek, researchers are still seeking to make sense of nitrogen trends. Before the current bridge replaced a narrow culvert, the upper reaches of the creek behaved like a freshwater pond, naturally removing nitrogen. Now, the flushing washes nitrogen away, but the upper reaches no longer remove the nutrients on their own. The change is actually beneficial for Harwich’s nitrogen reduction targets, Ridley said.

“In effect, Harwich will be getting more crediting for the sewer that it’s doing, because before it wasn’t going to get credit for the nitrogen that was being taken out by the natural system,” she said.

Early in its wastewater management strategy, Chatham decided to eventually extend the sewer system to all parts of town, even locations where nitrogen removal is not strictly necessary. As a result, the town will eventually get credit for removing more nutrients than the state requires. “There may be some opportunities for trading – nitrogen trading,” Ridley said.

Work is currently underway to evaluate exactly how such an arrangement might be made, but Chatham may have the opportunity to see some benefit by taking on some of the nutrient-removal liability of other Pleasant Bay towns where nitrogen removal is less cost-effective. A study currently underway will examine “how those kinds of arrangements could be pursued,” she said.

The new model also considers the benefits of nitrogen reduction strategies outside of sewer systems, like the pilot oyster grow-out operation in Lonnie’s Pond in Orleans. As a means of reducing nutrients entering a waterway, shellfish growing is far less expensive than expanding a sewer system, but it doesn’t remove enough nitrogen to achieve the goals set by the state, Ridley said.

“But it has worked. The nitrogen removal has been real and calculable,” Ridley said. “It’s just not scale-able at this point.”

The four Pleasant Bay towns have already received credit for adopting regulations that limit the use of lawn fertilizer, but Chatham Health and Natural Resources Director Robert Duncanson said that, as a scientist, he believes that such a rule is a “feel-good regulation,” since it is hard to measure its actual impact on reducing pollution.

“It’s the enforcement...that is really the difficult part,” he said. Fertilizer is believed to contribute about 5 percent of the nitrogen load entering local waterways, with the vast majority – around 80 percent – coming from septic systems.

The Chatham select board praised the Pleasant Bay Alliance for its leadership and its work. Select board member Shareen Davis said she appreciates the value of the regional approach.

“I really wish we had something like this for Nantucket Sound,” she said.