Summer Stresses Out Bottom of Narragansett Bay
October 4, 2009
“Fish need oxygen too,” read the bold, blue letters across Christopher Deacutis’ gray T-shirt as he helped haul up the Narragansett Bay Estuary Program’s $22,000 Sea-Bird — a 50-pound, cylindrical oxygen sensor.
It was the first day of September and Deacutis, the chief scientist for the estuary program, and his team of assistants — Lesley Lambert, Tim Delp and Heather Stoffel — were using the high-tech piece of equipment to record oxygen levels, temperatures and salinity, among other things, at 29 specific locations across Narragansett Bay.
The oxygen readings at the bottom of Greenwich Bay were, as expected, troubling.
Dissolved oxygen is necessary to sustain life in any estuarine system. In aquatic ecosystems, low levels — referred to as hypoxia — usually mean a concentration of 2 to 3 milligrams of oxygen per liter of water.
The saturation levels of dissolved oxygen in Narragansett Bay are typically 6 to 8 milligrams per liter, according to studies.
On this day, the bottom of Greenwich Bay was averaging about 1 milligram of oxygen per liter of water. At a bottom location in Greenwich Cove, just offshore from the East Greenwich wastewater treatment plant, the Sea-Bird recorded an oxygen reading of 0.4.
“There’s definitely no fish down there,” Deacutis said as he and Delp pulled the 5-year-old Sea-Bird from the water. “Anything below three starts causing stress. Below one milligram, you start killing things — fast.”
Mobile marine animals, such as adult fish, can often survive hypoxia by moving into oxygenated waters. When they can’t, such as when young fish need to spend time in a habitat that has become hypoxic, the result is a fish kill.
More than six years ago, Narragansett Bay experienced what many believe to be the worst fish kill in these waters in the past 50 years. More than a million fish, primarily juvenile menhaden, floated to the surface on Aug. 20, 2003.
Hundreds of small crabs, blue crabs, grass shrimp, blackfish, horseshoe crabs and American eels also suffocated.
Two other times in the past nine years — 2001 and 2006 — Narragansett Bay has experienced large fish kills because of a lack of oxygen in the water.
While the direct effect of hypoxia is fish kills, such events also deplete valuable fish stocks, damage the ecosystem and hurt the tourism industry.
So massive was the 2003 fish kill, that it grabbed the attention of Gov. Donald L. Carcieri and state legislators who responded by establishing committees to study the issue of hypoxia and what can be done to control it.
Summer in particular is a stressful three months for the waters of Narragansett Bay, as heavy rains and warm temperatures create nasty conditions for marine life, especially for bottom-dwelling species.
These conditions combined with excess nutrients, specifically nitrogen, deplete oxygen, cause algae blooms and devastate fragile ecosystems.
A decade ago, Deacutis was one of the first to introduce evidence that low levels of dissolved oxygen were degrading the integrity of Narragansett Bay. Deacutis presented his findings in 1998, and since then a group of scientists, researchers and volunteers have been monitoring the bay’s oxygen levels every summer.
The oxygen levels fluctuate depending on many factors, most notably rain, temperature and wind strength and direction, but low levels are routinely recorded from mid-June to mid-September at the western edge of Greenwich Bay and in the Providence River.
“The worst water is on the bottom,” Deacutis said. “The oxygen at the bottom is used up quickly until a big event like a storm mixes everything up.”
Until then, however, life at the bottom of certain areas of the bay can be a struggle for such species as scallops, soft-shell clams, blue mussels, razor clams and shrimp.
“Sensitive species are fine until the summer turns the water nasty,” said Deacutis, who has a Ph.D. in oceanography. “Quahogs are fine year-round because they can hold their breath for a month, but soft-cell crabs can only hold their breath for two weeks and scallops for about an hour.”
Problems caused by low oxygen levels are exacerbated by stormwater runoff and effluent from wastewater treatment facilities and septic systems that contains high levels of nitrogen and phosphorus.
Nitrogen and nutrient pollution remain the single greatest threat to the ecological health of Narragansett Bay, according to Jonathan Stone, executive director of Save The Bay.
Algae thrive in waters that contain excess nutrients. These tiny, single-celled plants bloom in huge numbers, coloring the water and decreasing its clarity. Algae typically live for only a few days to a week and then sink to the bottom, where oxygen-sucking bacteria feed on the dead matter that has blanketed the bottom.
It’s a vicious cycle that has created places, such as the bottom of Greenwich Bay, that are a barren wasteland for much of the year.
“Until the early 1950s, there was just summer housing along (Greenwich) bay,” Deacutis said. “Now a high density of year-round housing with sub-par septic systems is loading up the bay with nutrients. Sandy soil in the area allows the stuff to flow quickly into the bay.”
Since oxygen levels typically are lowest in estuaries and coastal areas, where the water is poorly mixed and where harmful runoff is collected, nursery habitat for fish and shellfish often is affected. Without nursery grounds, young marine life can’t find the food or habitat it needs to reach adulthood.
This type of oxygen-deprived, nutrient-rich environment can quickly weaken, reduce or kill off important fish and shellfish stocks.
Greenwich Bay was once one of the richest bay scallop areas in Rhode Island. It’s no coincidence that today it lacks a significant scallop population and has no substantial eelgrass beds.
In 1999, less than a year after Deacutis introduced evidence of the bay’s low oxygen levels, the Narragansett Bay Estuary Program organized a volunteer effort to investigate summertime oxygen levels.
For the past 10 years, a collaborative group of scientists and environmental professionals — dubbed “The Insomniacs” because they used to work at night — from the estuary program, the University of Rhode Island, Brown University and Roger Williams University have been collecting data from the same 75 locations throughout Narragansett Bay.
The positions were chosen based on various depths and in a pattern that allowed “us to map across a large area,” Deacutis said.
Teams in two to three boats take readings at the 75 sites six times a year — once in June and September and twice in July and August.
The first five years of this summertime survey were conducted with volunteers. There were no funds — federal, state or otherwise. There wasn’t even gas money for the boats.
For the past five years, the project has been funded through a shared federal grant from the National Oceanic and Atmospheric Administration. The project costs about $40,000 annually and Deacutis said there is enough money to fund the work through next summer.
Since 2004, The Insomniac project has worked in tandem with a study being coordinated by six agencies, including the Narragansett Bay Commission, Save The Bay and the Department of Environmental Management.
Monitoring stations attached to 13 buoys around Narragansett Bay are fitted with instruments that collect water-quality data every 15 minutes. These buoys collect similar information — temperature, salinity, chlorophyll and dissolved oxygen — as the 75 Insomniac sites but in different parts of the bay.
“The further you go down the bay, the better the oxygen levels get at the bottom,” said Stoffel, a marine research assistant at URI. “Off Prudence Island and at the tip of Newport there are better oxygen levels because oceanic waters are coming into the bay there.”
With federal money in short supply, however, Deacutis is worried about the future of his survey work and the meaning of 10 years’ worth of data.
“If the federal money disappears, the monitoring stops,” he said. “We lose our ability to interpret change. Was it a freak event, part of a cycle, are things getting better or are they getting worse?
“It’s like taking medication for high blood pressure but then never taking your blood pressure again. Is the medicine working? Do we increase or decrease the dosage? Monitoring lets us know if management is working.”
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