The Battle Continues

The Battle Continues

Eelgrass, nitrogen, and the complexities of sewage
Friday, June 13, 2014

Fred ShortOn an August morning shimmering with late-summer heat, Fred Short, research professor of natural resources and marine science, leans over the gunwales of his skiff, strands of emerald eelgrass draped across his open palm. "Here, look at this," he says. "The blades are too thin." He runs his long-handled hook through the water, stirring up a swirl of sediment. The eelgrass here grows in sparse clumps along the bottom, sometimes hard to spot in the murky stew of loose sediment. "This was a lush bed last year," he says, hooking another piece of vegetation. This time, it's a dripping chunk of sea lettuce, an invasive seaweed that thrives on nitrogen, hogging the light from above and eventually suffocating the delicate eelgrass.

Short has been keeping an eye on the bay for 30 years—and what he sees has him worried. Not only is the total area of eelgrass coverage shrinking, but density within the beds has also decreased dramatically. He steers the boat to a healthy bed, and it's easy to see the difference. Here, the water shimmers clear and green, the sediment anchored by thick mounds of emerald eelgrass waving just below the surface. These days, he doesn't see beds like this one very often. Many are at 40 or 50 percent of their original density. In adjacent Little Bay, the eelgrass has vanished. It's also disappeared along some stretches of heavily developed shoreline in Great Bay.

Zostera marina, commonly known as marine eelgrass, has been putting down roots for thousands of years, but until recently, most people had never heard of it. Today this underwater flowering plant, often called an "ecosystem engineer" for its ability to stabilize the seabed and slow currents, has become the unlikely focus in a new battle for the bay. The enemy this time is nitrogen, hidden in wastewater treatment plants and septic tanks, parking lots and lawns, rain and snow and the air we breathe. There are other threats, too—phosphorous, chlorophyll, hydrocarbons, sediments—all of it accumulating over time and, if left untreated, slowly smothering the life out of the bay.

And so the EPA recently stepped in with a new rule: 3 milligrams per liter is the new maximum acceptable concentration of nitrogen in water discharged from treatment plants. It's a number with daunting implications for communities throughout the Seacoast, which collectively dump 20 million gallons of wastewater into Great Bay each day—none of it treated for nitrogen. In fact, the wastewater discharge from some of the towns has been measured at up to 10 times the EPA's acceptable level. For some communities, achieving compliance could require hugely expensive updates for outdated treatment plants, leading to the doubling or tripling of resident sewer fees.

And there's another issue. Wastewater treatment plants are only one source of the problem. Of the 1,200 tons of nitrogen that makes its way into the bay each year, as much as 70 percent comes from so-called nonpoint sources—runoff from roadways, parking lots, farm land, and lawns, as well as groundwater that picks up the outflow from countless septic tanks. "While everyone agrees that we need to care for the bay, opinions differ on what that means and where the source of the problem lies," says Rachel Rouillard, director of the Piscataqua Region Estuaries Partnership, a UNH-based, EPA-funded collaborative program that works to protect the health of the bay.

Eel grass in Great BayThose in favor of accepting the new limits argue that working on wastewater nitrogen is the fastest route forward—an identifiable source that can be targeted and fixed. They also point out that more than half the nitrogen overload in the bay comes from human waste, much of it from sewage treatment plants. But communities battling the EPA say it's unfair to focus on treatment plants when so much of the problem is caused by nonpoint sources, and some insist that the science is inconclusive. Indicator species like eelgrass, they say, are affected by weather, disease, and natural cycles, making definitive conclusions difficult.

Some towns have been so adamant about opposing the new EPA discharge levels that they banded together to form the Municipal Coalition to challenge the new limits. The town of Newmarket, meanwhile, decided to forge ahead on a sewage treatment upgrade, thanks in large part to education efforts that featured scientists like Michelle Daley, associate director of UNH's Water Resources Research Center, who reeled off a slew of facts during information meetings: Dissolved inorganic nitrogen is up 42 percent in the past five years. Eelgrass biomass declined by 64 percent between 1990 and 2008. Oyster populations have plummeted. Last spring, the town voted 81 percent in favor of funding upgrades for the treatment plant, becoming the first community in the Great Bay watershed to accept the new EPA permit. But solving the sewage problem isn't enough, warns Peter Wellenberger, who participated in the education efforts behind the Newmarket vote. "The question is," he says, "how much more can the bay take?"

As Short wraps up his 2013 eelgrass survey, he pauses and looks across the water, his arm sweeping toward the horizon. The scene speaks for itself. The tide is going out, slowly exposing an expanse of eelgrass growing along the edge of a vast mudflat. Along the line of receding water, a gathering of herons, egrets, and other wading birds stand poised, waiting, a cluster of spindly legs and beaks silhouetted against the morning sky. The rolling water carries all the tiny fish and other invertebrates that depend on eelgrass for survival, serving them up to the winged customers, who snap their beaks and haul up breakfast as it rushes past. "It's the ultimate bird buffet," says Short, who worries that time is running out. Eelgrass is resilient, he notes, recounting success stories where nitrogen cleanup has sparked a return of aquatic vegetation. But if we wait too long, he warns, the buffet may close for good.

Originally published by: 

UNH Magazine

Written by Suki Casanave '86G

Photos by Lisa Nugent