The Massachusetts Estuaries Project (MEP), a state and local collaborative, completed its report on the Menemsha-Squibnocket pond embayment system and gave a presentation of its findings on August 23.
Beginning in the ’90s, MEP was created to “help determine current nitrogen loads to southeastern Massachusetts estuaries and evaluate reductions that would be necessary to support healthy ecosystems,” according to the MEP website. MEP has worked on 89 estuaries throughout southeastern Massachusetts, completing 10 estuary studies on the Island.
The Menemsha-Squibnocket project was a huge partnership effort involving the Massachusetts Department of Environmental Protection, University of Massachusetts Dartmouth School of Marine Science and Technology, the Martha’s Vineyard Commission, the towns of Aquinnah and Chilmark, and the Wampanoag Tribe of Gay Head (Aquinnah).
Brian Howes, director of the Coastal Systems Program and a professor at UMass Dartmouth School for Marine Science and Technology, gave the presentation at the Aquinnah town hall.
“The real problem for the south coast of Massachusetts and its estuaries … is that we’ve been seeing since 1950 or so,large increases in population, in the summer or year-round or both, where we’re increasing the nitrogen loading that is associated with that development. It’s going into the ground, it takes a long time, eventually it reaches into the estuaries,” Howes said. “Sometimes we’re passing the limit for what [the estuaries] can tolerate without being degraded. They are now being degraded.”
Nitrogen and phosphorus are both nutrients vital to the growth of coastal ecosystems, according to the MEP. These nutrients support the growth of aquatic plants, which provide food to fish, shellfish, and other organisms. Too much of these nutrients can have negative effects on ecosystems, resulting in a decline of aquatic plants and wildlife.
A 200-page report on the Menemsha-Squibnocket project concluded the primary sources of all this nitrogen are from “wastewater disposal, fertilizer, and changes in the freshwater hydrology associated with development.”
The MEP began its study of the pond by using an analytical method called the Linked Watershed-Embayment management modeling approach. This approach determines an embayment’s nitrogen sensitivity, nitrogen threshold loading levels, or the amount of nitrogen it can handle before degradation occurs, and its response to changes in loading rate. Howes and others with MEP began taking water samples to come up with a benchmark for how much nitrogen was normal for the ponds to have.
After measuring nitrogen levels in both ponds and monitoring how the water flows through Herring Creek, MEP discovered that Squibnocket is causing some degradation in Menemsha. “It’s not Squibnocket’s fault,” Howes joked, “it’s just passing water.”
Howes said there are two primary ways to restore degraded estuaries — control the introduction of nitrogen, or control the output through tidal flushing.
For Menemsha’s main basin and the Nashaquitsa Pond, the goal is to reduce nitrogen loading by less than 20 percent to achieve the target threshold. Howes added that if the threshold is lowered in Squibnocket, it will improve Menemsha.
For Squibnocket, the threshold can’t be reached solely through nitrogen load reduction, but with more tidal circulation. The tidal prism, which is the volume of water in an estuary between the average high and low tides, would have to be increased 20 to 25 times. “It’s not a big change,” Howes said in terms of what people would actually notice, but, “It’s a big change for the ecology of the pond.”
Overall, Menemsha Pond is in good shape, according to Howes, because it receives tidal circulation from the ocean. Squibnocket Pond has much higher nitrogen levels because water does not have any real water circulation, and only receives overflow of ocean water during “significant storm events.”
“You have a bucket that doesn’t exchange water and you keep dumping nitrogen into it all the time, what do you think is going to happen?” Howes said. The sub-embayments of Nashaquitsa Pond and Stonewall Pond are of the most concern due to their lack of water circulation.
Along with water circulation, educating people on fertilizer use, looking at a decentralized wastewater system, and maximizing natural attenuation, nature’s process of cleaning underground pollution, are all options to look at going forward to lower nitrogen levels.
Howes added that estuarine recovery is “relatively rapid” once a recovery plan is implemented. Habitat and water quality can improve within three to five years, but it depends on significant funding efforts from local towns.