Swimming With the Fishes in LI Sound? Not if Hypoxia Kills Them First

Environmentalists keep a wary eye on August, when warm weather and discharge from sewage treatment plants contribute to hypoxia, making parts of the Sound uninhabitable to marine life.

Severe hypoxic conditions in Aug. 2012. Black, red indicate severe hypoxia. Vast orange areas off coastal Fairfield and Westchester towns mean under 3 milligrams of oxygen/liter, enough to destroy fish habitat in deeper waters. Image: Save the Sound
Severe hypoxic conditions in Aug. 2012. Black, red indicate severe hypoxia. Vast orange areas off coastal Fairfield and Westchester towns mean under 3 milligrams of oxygen/liter, enough to destroy fish habitat in deeper waters. Image: Save the Sound

Written by Leslie Yager

Last summer, hypoxia took a toll on Long Island Sound.

A threat to the Sound’s ecosystem that makes water uninhabitable for fish in deeper waters such as bluefish, fluke, blackfish and flounder, hypoxia results from excess nitrogen and lack of oxygen in the water.

Nitrogen comes from a variety of sources including discharge from sewage treatment plants and as a consequence of warm weather. And, western Long Island Sound, which is both narrower than eastern parts of the Sound and has more treated sewage, results in a greater risk of hypoxia, experts say.

In warm weather, nitrogen acts as a fertilizer, spurring the growth of algae, according to Mark Tedesco, director the US Environmental Protection Agency's Long Island Office.

When the algae die, the decomposition process removes oxygen from the water, he said. Every summer, nitrogen pollution results in parts of western Long Island Sound losing nearly all their oxygen and hypoxia.

Tedesco likens the Sound to a compost heap and the excessive nitrogen to too much fertilizer.

“We don’t want to overfertilize the plants in the Sound. The organic matter sinks to the bottom, breaks down and uses up oxygen," he said. "We are trying to reduce the amount of nitrogen that goes in the water.”

According to the Connecticut Department of Energy and Environmental Protection website, hypoxia impacts up to half of the Sound’s waters each summer.

But 2012 was particularly bad, said Tom Andersen, New York director of programming and communication for Westchester Save the Sound, which has been monitoring the Long Island Sound for decades.

He said that the winter of 2012 was particularly warm, and contributed to unusually severe hypoxia last August. Andersen who also blogs on Patch for Save the Sound referred to hypoxia as “the chief threat to Long Island Sound’s ecosystem.”   

In fact, last summer, water from the Sound was so warm that Millstone Nuclear Power Plant in Waterford had to be shut down because it relies on water being under 75 degrees to cool down the reactors.

According to Andersen, who authored the book, This fine piece of Water: An Environmental History of Long Island Sound," in addition to the weather aspect of hypoxia, nitrogen in treated sewage is problematic. Andersen explained that twenty years ago New York, Connecticut and the federal EPA agreed that sewage treatment plants would have to reduce the amount of nitrogen released in the Sound and set strict goals with a deadline of 2014. Connecticut, according to Andersen, is very close to meeting the goal, but New York is a different story. 

New York, which includes four expansive sewage treatment plants in the East River/Sound area and  Westchester County, with four plants that discharge into the Sound in New Rochelle, Mamaroneck, Rye and Port Chester, received a 3-year extension, bringing their deadline to 2017. Save the Sound is watching them closely.

In normal healthy times, Sound waters should have about 8 milligrams per liter of dissolved oxygen, but typically that ideal only occurs in late fall, winter and early spring. 

Last summer, following the warm winter, part of the Sound had hypoxia hot spots in locations that correspond on a map to the sewage treatment plants.  The threshold for sounding an alarm is 3.5 or 3 milligrams per liter. But really at 2.0 milligrams per liter or less, conditions are so bad that the Sound becomes uninhabitable, experts say.

According to Andersen, “The fish that live in the deeper water of the Sound include fluke, striped bass, flounder and blackfish and those fish sense that conditions are changing and they get out.  The fish leave or die when dissolved oxygen gets below 3 milligrams/liter.”

According to Tedesco, marine life is dying. It just can’t breathe and hypoxia creates dead zones. The situation means more than a problem to fish, considering the Sound is part of the area's economy, affording both commercial and recreational fishing.

“The Sound will never look blue like the Caribbean," said Tedesco. "It will always be a richer, more productive area than the Caribbean, but we want a healthy system. We don’t to ‘overfertilize.’ We don’t want green soup.”

Tedesco explained that in the western end of the Sound, there are not only more sewage treatement plants, but the Sound is narrower, which means a lower level of 'water mixing.' Specifically, oxygen gets in from the air and from plant growth at the water’s surface. Also, storms mix up the water from the surface to the bottom. There is plenty of oxygen in the surface water. It’s deep down where there is less," said Tedesco, adding, "Each summer we go through this dance of mixing and how severe the hypoxia will be.”

With August certain to bring heat and July having packed a sweltering wallop on the Sound, environmentalists are waiting and watching. According to Christopher Bellucci of DEEP’s monitoring and assessment program, the situation is unpredictable. “Hypoxia may still occur in August. It’s a complex mix of water temperature, wind, precipitation, and biological interactions with organisms in the Sound.”

And so the dance that Tedesco referred to goes on. Save the Sound, DEEP and EPA are all monitoring the situation closely. So too are the fish who hope to keep swimming.


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