A recent study shows that eelgrass in parts of West Falmouth Harbor is growing relatively healthily, but Philip Colarusso of the US Environmental Protection Agency said last week that it could take between six and 17 years before eelgrass beds fully recover.
Dr. Colarusso, an eelgrass expert, presented the results of the study to the Falmouth Water Quality Management Committee during its meeting last Thursday, June 15. The study, “Factors Affecting Carbon Accumulation in New England Eelgrass Meadows” was a collaborative effort of the EPA, Massachusetts Office of Coastal Zone Management and university researchers.
Project researchers analyzed eelgrass beds along the coasts of Massachusetts, New Hampshire and Rhode Island, and took measurements of eelgrass density, growth, carbon sequestration and other data points.
Eelgrass stabilizes sediment; is a vital base in the oceanic food chain; and absorbs water pollutants. In addition, eelgrass serves as a nursery habitat, providing vital habitat for bay scallop spat, which can escape ocean floor predators by clinging to the grass.
Research also shows that eelgrass can sequester carbon, serving as a combatant against climate change, Dr. Colarusso said. The current global loss of seagrass, mangroves and salt marshes is equivalent to releasing greenhouse gas emissions equal to that of Germany and Poland combined.
Eelgrass samples were taken from the mouth of West Falmouth Harbor last July over a two-week period, and Dr. Colarusso said the samples likely represent the best-case scenario for eelgrass in the harbor, since the beds were closer to Buzzards Bay.
The study did not address eelgrass abundance or changes over time at the mouth of West Falmouth Harbor.
While Dr. Colarusso did not make any claims about whether eelgrass was making a comeback in West Falmouth, he did say in an e-mail on Tuesday, June 20, that “for several of the parameters that we measured West Falmouth compared favorably with the majority of the other meadows.”
Compared to other locations, eelgrass in West Falmouth fell on the lower side for growth, and was a little below the mean for production (a combined measure of density and growth), at 4,000 milligrams per square meter.
However, West Falmouth proved healthier compared to other locations in regards to shoot density and percentage of nitrogen in the plant tissue, which is an indicator of nitrogen pollution.
The eelgrass bed had a density of about 500 shoots per square meter, the fourth highest density out of the eight test sites. Of the test sites, West Falmouth had the lowest nitrogen content in plant tissue: West Falmouth samples measured under one percent nitrogen, compared to about 1.2 percent in Orleans and about 1.7 percent in New Hampshire’s Great Bay.
Water quality management committee member Matthew A. Charette asked how long it would take eelgrass to come back once water quality improves in West Falmouth Harbor.
Eelgrass rebound rates vary widely, Dr. Colarusso said; the city of Gloucester reduced nitrogen by redirecting outfall from a wastewater treatment plant in Gloucester Harbor into Mass Bay in the early 1990s, and saw a lag time of about seven years before eelgrass beds returned.
A similar project in Boston Harbor, however, saw steady improvement over the course of 15 to 17 years. However, Dr. Colarusso said those observations were made in “arguably the most contaminated parts of the harbor” where the sediment had the consistency of black mayonnaise.
“If it has anoxic sediments, it will be a while for Mother Nature to remediate,” he said.
West Falmouth Harbor suffers from the effects of nitrogen pollution largely as a result of the West Falmouth wastewater treatment plant that went online in 1986.
The nitrogen plume reached the harbor in 1994, and as a result, eelgrass beds were deeply impacted; based on satellite imaging coverage data comparing eelgrass in 1951 to 2001, the Massachusetts Estuaries Project Report estimated that about 40 acres of functional eelgrass were lost out of a total of 84 acres, nearly 50 percent.
Committee chairman Eric T. Turkington said the town has yet to see a significant rise in water quality or decline in nitrogen concentrations in the harbor as a result of the new West Falmouth wastewater treatment plant, but expected to see improvement now or in the very near future since the facility was renovated.
The town has also experimented with aquaculture operations and installation of innovative/alternative septic systems at 20 waterfront homes in West Falmouth to decrease nitrogen input to the harbor.
“I think it’s fair to say that we’re starting to look for that impact. People are a little surprised they haven’t seen it, because it’s theoretically been enough time for the old plume to [have] worked its way through… [but] plumes don’t behave,” Mr. Turkington said Tuesday, June 20.
A sentinel station located in West Falmouth’s inner harbor measures water quality and nitrogen content. That station is monitored by the School for Marine Science & Technology (SMAST) at University of Massachusetts Dartmouth under a contract with the town.
Eelgrass is particularly vulnerable to the impacts of nitrogen pollution, because resulting algal blooms block ambient light from reaching the ocean floor.
Dr. Colarusso said eelgrass relies heavily on sunlight compared to other ocean flora; studies indicate that eelgrass seedlings may need as much as 50 percent of ambient light to thrive, and adult eelgrass plants can thrive on 20 percent of ambient light. For comparison, phytoplankton need and use about 1 percent of ambient light.
Symptoms of nitrogen pollution in eelgrass beds include a decline in shoot density as eelgrass thins to optimize light reception, reduction in plant biomass, proliferation of drift algae and a decline in the deep edge of the meadow, meaning eelgrass creeps into shallower water.
Rather than wait out the lag time and allow eelgrass to return on its own, Mr. Charrette asked whether it would be possible for the town to plant eelgrass beds in West Falmouth Harbor.
“It’s possible,” Dr. Colarusso said, but planting eelgrass is labor intensive, inconsistent and can be expensive.
Dr. Colarusso is currently leading a project for the US Navy in Newport to plant 1,700 eelgrass seedlings as a small experimental bed. The seedlings are harvested from other healthy locations, preferably within water bodies of similar temperature, and are then planted two to three meters under the surface.
Dr. Colarusso said there are eelgrass beds in Menemsha that would serve as good donors for parts of West Falmouth Harbor.
However, Mr. Turkington said on Tuesday, June 20, that eelgrass planting is not something the committee is currently considering.
Given that planting would be expensive and difficult, and that eelgrass will likely replant itself, Mr. Turkington said such an operation would not be beneficial. He added that if the committee considers planting as an option, it would not be until water quality improves in the harbor.
“We’ve thought about it, but there’s really no point in planting it until your water quality improves.”
Dr. Colarusso hopes to conduct satellite analysis of West Falmouth Harbor, which could provide baseline data on the amount of eelgrass beds currently within the harbor.
The United States Geological Survey has also recently completed a drone survey of the harbor, using technology that measures underwater movement to identify eelgrass beds moving with the waves and calculate their size.