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.

View Implementation Actions for Nitrogen Loading

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Progress (to 2017 Target)

The 2017 Target 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.

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

The 2000 Total Maximum Daily Load (TMDL) agreement between EPA and Connecticut and New York called for a 60 percent reduction from the baseline level of 59,000 trade equalized pounds per day of nitrogen. This reduction goal had been met in 2016 and has continued to decline. The combined total equalized point source average daily load for 2022 was 17,509 lbs/day, the lowest on record, and is a rewarding 5,266 lbs/day below the TMDL target. This represents a 70.3 percent reduction from the baseline established in the 2000 TMDL.

Through the middle of the last decade, there was a significant trend of year-to-year declines in the amount of nitrogen discharged from wastewater treatment plants into Long Island Sound as more advanced Biological Nutrient Removal (BNR) systems came online at the plants. With most of the upgrades accomplished by 2016, nitrogen loads have fluctuated up and down by relatively small amounts. These fluctuations are mainly due to weather conditions, such as high precipitation rates and cooler spring temperatures, that impact the efficiency of nitrogen removal at wastewater treatment plants. Note heavy precipitation events are increasing in frequency and as such are actively being tracked by the Long Island Sound Study.

Greater than normal amounts of precipitation are believed to be primary causes of increased nitrogen discharge into the Sound from Connecticut and New York in 2018 and 2019. Heavy rainfall and elevated groundwater levels infiltrating wastewater treatment plants can decrease the BNR systems ability to efficiently reduce nitrogen. If that happens, the effectiveness of treatment technologies to break down nitrogen into a harmless gas can be reduced. In 2020 and 2021 it is believed that due to slightly less rainfall and warmer daily temperatures than 2018-2019, it enhanced the BNR systems to work more efficiently in the nitrification process enabling several large wastewater treatment plants in the watershed to remove over 3,880 pounds more per day (on average) than the previous two years.

In 2020 and 2021 the treatment plants experienced less rainfall and warmer daily temperatures than 2018-2019, which enhanced the BNR systems to work more efficiently in the nitrification process. More efficient BNR systems enabled several large wastewater treatment plants in the watershed to remove over 3,880 pounds more per day (on average) than the previous two years.


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 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 (CT DEEP) and New York State Department of Environmental Conservation (NYSDEC).


  • 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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