Great Bay Estuary Faces Pollution Threats
At 18 miles long, the New Hampshire coastline is the shortest in the country.
But if you include the Great Bay, the state’s meager coast grows by about 144 miles of tidal shoreline.
The rare inland estuary, where salt water meets fresh, spans more than 13,000 acres.
And nearly a quarter of the state’s population lives within its watershed.
In the first of a five part series on the Great Bay, NHPR’s Environment Reporter Amy Quinton takes an in-depth look at the pressure that many people put on the fragile ecosystem.
It’s not yet 7 am, just before low tide, at the University of New Hampshire’s Jackson Estuarine Laboratory in Durham.
From the docks here at Adams Point, fog delicately hovers over the still waters of the Great Bay.
Fred Short, a research professor of Natural Resources and Marine Science, and his three-person crew head out on a boat to the center of the Bay.
(sound of boat) For the past 26 years, Short has been studying the estuary’s eelgrass.
A few years ago, he and other scientists found a disturbing trend.
The underwater plant is disappearing.
“Really around 2005 it first started," Short says. "We were able to document it, three years later we had lost all the eelgrass in Little Bay and Piscataqua River, and the grass in the Great Bay here is down to about half of what it was historically.”
Eelgrass is the foundation of the estuary; it acts as a water filter, and it provides a vital habitat for wildlife.
“It’s an area where organisms come to lay their eggs, because there’s a lot of food in there," Short continues.
"There’s a lot of things growing on the eelgrass, animals and plants, little fish and crabs and shrimp can feed on. It becomes a nursery ground for the estuary.”
During low tide, more than half of the Great Bay estuary is exposed mudflats and eelgrass.
Riding out on the boat, we see Blue Herons and other shorebirds feast on the small fish that didn’t make it off the flat into the channel.
To get from the boat to the eelgrass beds, Short and his crew don wetsuits and booties and tromp through the shallow waters for about 50 feet.
Our feet sink deep into the muddy bottom, making it a tough trek.
As we approach the eelgrass beds, Short sees signs of unhealthy waters.
He pulls out what looks like a giant lettuce leaf. Short: “What happens here - which is a very clear signal of increased nitrogen - is we get growth of macroalgae in the beds where ulva, this green sea lettuce, just proliferates all over the bay and crowds out the eelgrass.”
Short says the culprit is nitrogen.
Nitrogen is a nutrient which feeds plants. But too much of it can cause these nuisance seaweeds to grow, block out light, and smother eelgrass.
Nitrogen’s impact in the center of the Bay doesn’t stop there.
Research assistant Nicole Sarratte takes out a what is called a quadrat. It’s an 18 inch square made of wire.
She uses it to measure the vegetation at the bottom. Sarratte demonstrates: “So you’d place your quadrat down, and you’d give a total percent cover on the large quadrat. Here’s its forty.”
All the areas here have eelgrass cover, but Short says it’s sparse.
Short: “You see here, you look down and you can see the plants, but you can see a lot of bottom, didn’t used to be that way. The density used to be twice what it is now and because of all the algae and the poor water quality conditions the plants just don’t grow as dense and as thick as they used to.”
In addition to feeding nuisance seaweeds, nitrogen also spurs the growth of algae and other phytoplankton that block the sunlight the eelgrass need.
And as the eelgrass thins, it becomes more susceptible to sediments.
Dr. Richard Langan, the Director of UNH’s Ocean and Technology Programs, says sediments may be a bigger problem than nitrogen.
Langan: "Sediments that wash into the estuary from our rivers and streams or over land flow and also from re-suspension in the estuary, the biggest increase that we saw was with sediments, it was 123% increase in the period of time in the early part of the decade to the second half of the decade."
Regardless of what does more harm, it’s all driven by population growth.
Sewage plants dump treated wastewater directly into the bay or its seven tributaries, accounting for about a third of the excess nitrogen.
The rest comes from indirect sources like stormwater runoff, rain carrying fertilizers, pet wastes and spills from septic systems into the estuary.
42 communities are part of the Great Bay’s watershed.
So runoff from all those impervious surfaces, the paved roads, parking lots and rooftops, can pack quite a punch.
The Piscataqua Region Estuaries Partnership, or PREP, is dedicated to monitoring and protecting the Great Bay.
PREP scientist Phil Trowbridge says population growth, combined with unchecked development, is the most pressing threat.
Trowbridge: “We’ve seen a steady growth of adding 1500 acres of impervious surface in the watershed each year for the last 15 years, that adds up to about seven percent of the whole watershed being impervious surface.”
Studies have shown that if 10 percent or more of a watershed is impervious, water quality declines, habitat is lost, and biodiversity is reduced.
PREP conservation program manager Derek Sowers says the Great Bay Estuary is at a tipping point. Sowers: “We feel like we’re reaching a point where there’s a lot of warning signs that it could be passing a threshold which would make it very difficult to recover.”
The eelgrass loss is a very significant warning sign.
Back on the boat, Fred Short says eelgrass can’t be restored until the water quality improves.
He says his worst fear is that the Great Bay becomes a copycat of the Chesapeake Bay, where nitrogen and sediment led to the loss of more than 150,000 acres of bay grasses.
Short: “I’m very depressed about it actually. I saw the same thing happen to my seagrass colleagues in Chesapeake Bay in the 70’s and 80’s where the grass just disappeared from the Bay under their feet, we’re so rural and so far removed from all that that it didn’t seem like it could possibly hit here, but it’s basically the same scenario.”
Many scientists are hopeful that it’s not too late to keep the Great Bay from becoming the Chesapeake Bay.
Too much nitrogen in that estuary has created dead zones.
However, it will likely take decades and cost millions of dollars to restore the Great Bay to its former health.