When Superstorm Sandy hit the Rhode Island coast in October 2012, its waves and storm surge carved a large channel, or breach, between Trustom Pond and the ocean. For five months, saltwater poured into the pond, changing the water from fresh to salty.
Scientists are trying to determine what changes the breach caused in the pond, and whether breaches in general benefit the ecosystem. They are also debating whether to create breaches from time to time or leave the ecosystem alone.
U.S. Fish and Wildlife Service biologist Rhonda Smith, who has been studying the 160-acre pond and its wildlife and plants for four years, described the pond and the adjacent barrier beach as unique in Rhode Island.
“Trustom includes the only barrier beach, Moonstone Beach, and the only coastal pond in Rhode Island that are completely undeveloped and within the boundaries of a conservation area,” she said.
Smith noted that Moonstone Beach is an important nesting area for two shorebirds: the piping plover, a federally designated threatened species, and least terns, which are protected by the state.
“They both nest on Moonstone Beach in the summer, so we really try and set that beach aside for the birds as a nesting area for them. That barrier beach is a really important ecosystem,” she said. “Trustom has far and away more birds than any of the other beaches we monitor in Rhode Island. We manage 10 beaches in Rhode Island and Trustom so far has fledged four times more chicks than all the other beaches combined.”
University of Rhode Island wildlife ecology professor Peter Paton said the pond is also important to waterfowl, providing critical habitat during the winter. “This pond has a higher density and diversity of waterfowl than other coastal ponds in Rhode Island,” he said.
Trustom has undergone many breaches, both natural and engineered. Salt water frequently washes over the barrier beach and flows into the pond during storms like nor’easters, and full scale breaches — channels from the ocean to the pond — are created during extreme weather like hurricanes.
In the past, people regularly breached and drained the pond for agricultural purposes, and after the pond became part of the national wildlife refuge system in 1974, managers continued to breach it once a year, usually in the spring. In 1997, they decided to leave the pond to its natural processes. But when biologists discovered Eurasian watermilfoil, an invasive plant, in 2007, refuge managers decided to breach the pond again, hoping that salt water would kill it.
The largest natural breach in recent memory was created by Sandy. The channel from the barrier beach to the pond lowered the pond’s water level by 5 feet and quickly changed its salinity from fresh water to salty.
“The breach was open for a total of five months from October to March and our past records tell us that all those breaching events that happened before this one, from what we know, the breaches were typically open anywhere from a few hours to a few days, about a week maximum,” Smith said. “So very dramatic compared to past breaching events.”
Jim Turek, a restoration ecologist with the National Oceanic and Atmospheric Administration, visited the pond after Sandy and assessed the massive breach. “I reconned the site on 11-29-12 and the breach at that time was approximately 28-35 feet in width with an average discharge depth of about 1 foot at 1,100 hours,” he wrote in an emailed statement. “Over the winter, I noted that the breach increased in width and depth, thus increasing the extent of tidal exchange between the pond and Block Island Sound.”
Scientists are monitoring Trustom’s water quality, plants, fish, birds and other animals to try to determine how they were affected by the breach.
Salinity levels in the pond have declined since the breach closed in March, and the salt water is reverting to fresh.
The pond continues to suffer from an overload of nutrients such as nitrogen and phosphorus, which are carried in by tributaries that absorb fertilizers and agricultural and pet waste as they flow through populated areas.
Fish species change with the pond’s depth, salinity and pH levels. Smith said it was difficult to determine whether the same is true for waterfowl, because their populations are highly mobile, but some diving ducks like scaup and ruddy ducks were less numerous after the water level went down.
Smith said salt water entering through the breach wiped out freshwater plants, including two invasive species: milfoil and parrot feather. “We did not pick up any of these invasive plants at all, which was nice to see,” she said.
Whether breaches benefit the pond ecosystem, and whether refuge managers should occasionally supplement natural breaches with ones they create is the subject of debate among researchers.
Smith said more data were needed to determine the best course of action.
“Our conclusions in terms of the effect of the breach are going to depend on what the rest of our data tell us over time,” she said. “We’re still monitoring the birds out there, and we’re anxiously awaiting the water sampling analysis to see what differences we have there. We’re going to continue to monitor the plants and look for any of the invasive plants that might come back. It’s certainly possible that there are seeds down at the bottom of the pond from the milfoil that grow up next year if the pond is fresh water at that time. One of the questions that we have is should we keep using breaching as a way to manage the pond.”
Turek and Paton agreed that the pond should be allowed to evolve naturally.
“As a restoration ecologist, I believe that this is a natural process that should be allowed to occur,” Turek said of natural breaches.
“Water quality is a persistent issue at Trustom; thus the occasional breaching of the barrier beach at Trustom helps to maintain long-term water quality and wildlife use of this pond,” Paton said. “Permanent breaching of this pond would alter this ecosystem to one dominated by salt water, which would probably result in a long-term decline of biodiversity at this unique site.”