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Research & Monitoring

Status & Trends

LISS Ecosystem Targets and Supporting Indicators

Nitrogen Loading

Attain wastewater treatment facility nitrogen loading at the recommended 2000 Dissolved Oxygen Total Maximum Daily Load allocation level by 2017 and maintain the loading cap. Have all practices and measures installed to attain the allocations for stormwater and nonpoint source inputs from the entire watershed by 2025.

( Click labels in legend to hide data and adjust scale )
Progress (to 2017 goal)

The 2017 goal to reduce nitrogen loads discharged into Long Island Sound from wastewater treatment plants has been met.

Progress (to 2025 goal)

Data is not yet available for the second half of the target – reducing nitrogen from nonpoint source and stormwater inputs.

Trade Equalized (TE) Nitrogen Loads Discharged from CT/NY Wastewater Treatment Plants
Connecticut New YorkTotal (TE Pounds/Day)2017 CT/NY Goal

Status and Trends

The 2000 Total Maximum Daily Load (TMDL) agreement between EPA and the states of Connecticut and New York called for a 60 percent reduction from the baseline level of 59,000 trade equalized pounds per day of nitrogen. As of 2017 this goal has been met.  In 2018, however, nitrogen loads increased from the prior year for the first time since 2011.

A greater than normal amount of precipitation in 2018 is believed to be the primary cause of increased nitrogen being discharged to Long Island Sound from Connecticut. Heavy rainfall and elevated groundwater levels entering as infiltration and inflow into a wastewater treatment plant through the sewage collection system could fill a wastewater treatment plant’s processing tanks to near capacity or capacity. If that happens, the effectiveness of treatment technologies to break down nitrogen into a harmless gas can be reduced.

Typically, biological nutrient removal systems (BNR) do their best at removing nitrogen during the warmer, dryer seasons. But the second half of 2018 was very wet, resulting in Connecticut in a 24 percent increase in flows for the year. The average nitrogen concentration of discharges to Long Island Sound in the second half of 2018 in Connecticut also was significantly higher than in previous years. Combining increased concentrations and higher flows resulted in higher overall loads of nitrogen in the effluent of wastewater treatment plants discharging to the Long Island Sound watershed.

The total nitrogen loading to Long Island Sound in 2018 was still more than 42 million pounds less than the baseline loading from the early 1990s.


The second half of the target addressing stormwater and nonpoint source inputs will be more challenging since such inputs are widely dispersed.

An expanded EPA nitrogen strategy for Long Island Sound focuses not only on the nitrogen inputs from wastewater treatment plants, but also on the nonpoint contributions from tributaries and embayments. It also looks at ecological endpoints beyond hypoxia, such as eelgrass acreage, as increased eelgrass coverage is dependent on good water quality. An initial effort to develop nonpoint source tracking was summarized in a 2014 report (see Final Report link, data notes below)  which evaluates existing nonpoint source tracking tools for their applicability to Long Island Sound. This report suggested the adoption of the Chesapeake Bay Assessment and Tracking Tool (CAST) for use in Long Island Sound.  The report also outlines four tasks to be completed to allow CAST to be applied to the various sub-basins of the Long Island Sound watershed. In fiscal year 2019, NEIWPCC is receiving funding to conduct a pilot tracking tool project in Connecticut communities.

How is This Target Measured?

Nitrogen loading from wastewater treatment facilities is reported by the states of Connecticut and New York.

The nitrogen loading reported by Connecticut and New York is called trade-equalized because the amounts are corrected for the impacts of particular wastewater treatment facilities based on their location (see trade equalized nitrogen zones, sidebar).  The information needed for nonpoint nitrogen source controls will be produced by the tracking tools and models currently under development as described under Challenges.


Nitrogen is a plant nutrient. Large amounts of nitrogen loads into Long Island Sound can stimulate an excessive growth of plant plankton and macroalgae in a process called eutrophication.  

When plankton or microorganisms that eat the plankton decay, oxygen is consumed by bacteria and the bottom waters can become “hypoxic,” with less than 3.0 mg/l of oxygen. This can lead to stress or suffocation for slow moving animals, and cause other animals to scatter. Harmful algal blooms, some of which are toxic to humans, are another potential result of eutrophication.

Nitrogen typically comes from point sources, large fixed sources like wastewater treatment or industrial plants, or non-point sources, smaller diffuse sources like septic systems, stormwater, and agricultural runoff.


Dr. James Ammerman, Long Island Sound Study [email protected]


Source of Data

Connecticut Department of Energy and Environmental Protection (CTDEEP) and New York State Department of Environmental Conservation (NYSDEC).



Data Notes

  • The technical explanation on how the target was selected is found in Appendix B of the Comprehensive Conservation and Management Plan.
  • 2014 Final Report: An Evaluation of Nonpoint Source Pollution Control Measure Tracking Systems for Long Island Sound, prepared for the New England Interstate Water Pollution Control Commission by WaterVision, LLC, 30 pages.Open pdf.
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Related Ecosystem Targets

Learn More

Trade equalized nitrogen zones in CT and NY. The calculated impact of nitrogen inputs declines with increased distance from the Western Sound. see tmdl map description



Hunts Point wwtp: 42″ sludge pipe at West Aeration Tanks  Credit: NYCDEP

New York City has spent $1 billion to upgrade four wastewater treatment plants that has resulted in a 60 percent reduction in the amount of nitrogen being discharged into the Upper East River. These significant upgrades are helping the states of New York and Connecticut to meet their goal of preventing more than 45 million pounds of nitrogen a year from being discharged into Long Island Sound. See Jan. 5, 2017 news release from New York City Department of Environmental Protection. 

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