Study finds Narragansett Bay water quality improving after sewage plant discharge reductions

PROFESSOR CANDACE OVIATT, from the University of Rhode Island Graduate School of Oceanography, was part of a team of  oceanographers that completed a 10-year study of water quality in Narragansett Bay. They found that reductions in nitrogen discharged into the bay from sewage treatment plants has resulted in much clearer water and fewer algae blooms. / COURTESY UNIVERSITY OF RHODE ISLAND
PROFESSOR CANDACE OVIATT, from the University of Rhode Island Graduate School of Oceanography, was part of a team of oceanographers that completed a 10-year study of water quality in Narragansett Bay. They found that reductions in nitrogen discharged into the bay from sewage treatment plants has resulted in much clearer water and fewer algae blooms. / COURTESY UNIVERSITY OF RHODE ISLAND

NARRAGANSETT – A decadelong study of water quality in Narragansett Bay by oceanographers from the University of Rhode Island has found that reductions in nitrogen discharged into the bay from sewage treatment plants has resulted in much clearer water and fewer algae blooms.

“The water is clear, that’s for sure,” Professor Candace Oviatt of the URI Graduate School of Oceanography said in a statement. “But there is no pollutant in the water that is killing things and making it clear. It’s due to the lack of nutrients.”

However, run-off from heavy rain storms still creates poor water quality, according to information from the university.
Oviatt said regulations required the state’s 11 coastal wastewater treatment plants to reduce their discharges of nitrogen into the bay by 50 percent, something that was accomplished by 2013.

“The objective of our study was really to better understand hypoxia – a lack of oxygen – in the bay and determine how it was related to high nitrogen concentrations,” Oviatt said in a statement.

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Nitrogen from wastewater treatment plants is largely responsible for the excessive algae growth. Algae sinks to the bottom, rapidly using up all available oxygen in the water, the news release stated. It also can lead to large-scale fish kills, such as happened in Greenwich Bay in 2003.

Researchers collected data from 12 instruments in upper Narragansett Bay during the summer that measure water temperature, salinity, oxygen, chlorophyll and pH. They also analyzed monthly nutrient samples collected from 13 locations. And they created a series of computer models to predict how Narragansett Bay would respond to reduced nitrogen.

Oviatt said her data confirmed that the wastewater treatment plants achieved the 50 percent reduction in nitrogen discharges. That reduction has resulted in a 15 percent decrease in phytoplankton growth in the upper bay and 25 to 30 percent decrease in the mid-bay.

“I think we’re making progress, but in rainy years we’re still going to have hypoxia,” Oviatt said. “The next step is to keep an eye on how habitats respond. Are there more fish in the upper bay? Is there enough food available for aquaculture? The level of nutrients in the water now probably isn’t causing harm, but we should continue to assess it.”

Oviatt said that the one area of Narragansett Bay where water quality remains poor is Greenwich Bay, but it has little to do with wastewater discharges.

“The treatment plant there achieved its reductions, at least intermittently, but other nitrogen is coming into the bay through the groundwater that the plant has no control over,” she said. “The groundwater is picking up nutrients from cesspools and septic fields, and it will be a while before it wears out. The water quality there is still improved, but it’s got a way to go.”

She credited the state Department of Environmental Management and the wastewater treatment plants for the improved Narragansett Bay water quality.
“DEM did a wonderful job of imposing the regulations and making sure the treatment plants reduced their discharges,” she said.

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