Nitrogen Loading

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. Rainfall entering a wastewater treatment plant through the sewage pipe system or by depositing directly onto open process tanks at the plant can reduce the efficiency of the plant’s ability to treat and remove nitrogen before discharging into Long Island Sound.

Specifically, the wet, cold weather, especially at the end of the year, decreased the efficiency of nitrogen removal in wastewater treatment plant biological nutrient removal systems (BNR). In Connecticut, for example, the average nitrogen concentration of discharges to Long Island Sound in 2018 remained low (6.75 mg/l), but the increased flows into the treatment plant from storm sewer systems resulted in higher overall loads, demonstrating that wet weather diminishes the effectiveness of BNR systems to remove nitrogen.

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.

Challenges

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.

Importance

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.

Contact

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.