For oxygen in the Sound, which is more important: the size of a sewage plant or its location?

The answer may surprise you.

We put the question to Jason Krumholz, Ph.D., author of the Ask Dr. K blog on the Long Island Sound Study’s website. Jason has a doctorate in oceanography and is the National Oceanic and Atmospheric Administration’s liaison to LISS.

Low dissolved oxygen, or hypoxia, is the Sound’s most critical ecological issue. When warm summer weather and nitrogen from treatment plants combine to cause algal blooms, oxygen falls and large areas of the Sound’s bottom waters lose their ability to harbor healthy populations of fish and other marine life.

To ease the effects of hypoxia, communities along the Sound are required to remove 58.5 percent of the nitrogen flowing through their treatment plants; most have until the end of this year although several have a 2017 deadline.

The question came down to this: what contributes more to hypoxia, the sewage plants in Westchester, Nassau, Fairfield and Suffolk counties, which when the Sound cleanup started discharged a combined 14,000 pounds of nitrogen a day into the heart of the area hit hardest by hypoxia, or the treatment plants in Queens and the Bronx, which discharged 96,000 pounds a day but are further away?

Dr. K’s answer was that location is really important; on the other hand, size is really important too.

Engineers and others overseeing the Sound cleanup have calculated a “transfer efficiency rating” for each treatment plant that empties into the Sound, “which roughly approximates how much of each pound of nitrogen released from that plant makes it into Western Long Island Sound, where hypoxia is most severe,” Dr. K wrote.

The highest transfer efficiency rating belongs to Nassau, Suffolk, Fairfield, and Westchester counties. Nassau County has a rating of 1.0, which means that every pound of nitrogen released from Nassau into the Sound has an effect on hypoxia. The others are close: Suffolk, 0.94; Fairfield, 0.93; and Westchester, 0.83.

The treatment plants in Queens and the Bronx have ratings of 0.21 and 0.11. This map shows the how those overseeing the Sound cleanup have divided the Sound’s watershed into zones with the transfer efficiency rating for each zone show in parentheses.

transfer efficiency mapOn his blog, Dr. K wrote, “This is because they discharge into the East River, which is not actually a river, but a very fast moving tidal strait which connects Western LIS … to New York Harbor. The predominant direction of flow through this strait is out of LIS and into [New York Harbor], so much of the effluent discharged by these plants is rapidly removed from LIS through the East River. Because this water is so fast moving, there is not really enough time for phytoplankton blooms to form, and because the water is so turbid (from the combination of pollution and suspended sediment due to its speed) primary productivity is generally limited by light availability, not nutrients, so not much of that nitrogen is used by plankton in LIS in such a way that it might contribute to hypoxia (by dying and settling to the bottom and decaying).”

If that’s the case, why is New York City required to upgrade its treatment plants in Queens and the Bronx? The city has made significant improvements at Wards Island and Hunt’s Point and is continuing work at Bowery Bay and Tallman Island, at a cost of $1.157 billion. We emailed Dr. K to explain further.

He pointed out that while location is important, it’s not everything. Focusing on the four treatment plants in Westchester, he wrote:

“Keep in mind, as you mention, that the Westchester plants discharge roughly 40 million gallons a day [MGD], compared to 1,000 MGD+ from NYC.  …it’s safe to say that the NYC plants have a larger impact on hypoxia than the Westchester plants.”

If all of the nitrogen released from New York City’s plants contributed to the Sound’s hypoxia, their effect would be 20 to 30 times greater than Westchester’s treatment plants, he said. But because the tides and currents predominantly flow in the other direction, their effect is only two to five times greater.

Even if you broaden the analysis to include all the treatment plants in Nassau, Suffolk and Fairfield counties, the rough estimate is that the plants in Queens and the Bronx still have double the effect on hypoxia

That underscores the importance of completing the upgrades not just at the closest treatment plants, and not just at the biggest plants, but at both.

Save the Sound is advocating for federal and state funding so municipalities can make the necessary investments. Last year, Connecticut allocated nearly $1 billion over the next two years for the state’s Clean Water Fund. We’ve also taken the Great Neck Water Pollution Control District and the New York State Department of Environmental Conservation to court to help ensure that treatment plants meet their mandatory deadlines for upgrades.

But there’s still more to do—the hypoxia problem will take long-term commitment from leaders and citizens around the Sound. We urge New York residents to let their state elected officials know that they support increased funding for clean water, and to ask their local leaders to make sewage treatment upgrades a priority.

Read Dr. K’s blog here.

Posted by Tom Andersen, New York Program and Communications Coordinator for Save the Sound

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