LISS Meets its Nitrogen Reduction Target

Digester eggs at the recently upgraded Newtown Creek wastewater treatment facility (one of the largest which discharges into LIS) help break down sewage sludge to remove nitrogen. (photo credit


A major goal of the Long Island Sound Study since the 1980s has been to reduce the negative impacts of excess nutrients, primarily nitrogen, on Long Island Sound.These impacts include low bottom water oxygen concentrations or hypoxia in the western Sound, which can harm or kill animals that cannot

In 2016, Long Island Sound Study’s partners reached its target to reduce nitrogen loads by 58.5 percent. (pounds are in trade-equalized loads-see note at bottom) Credit: Long Island Sound Study

move to better conditions. Additional effects of excess nitrogen include toxic blooms of algae and reduced habitat areas for seagrasses which often serve as nursery areas for juvenile fish and other organisms. 


One of the major sources of this excess nitrogen, though far from the only one, is the effluent from wastewater treatment plants, particularly those concentrated towards the west end of Long Island Sound. In 2000, EPA and the states of Connecticut and New York adopted Total Maximum Daily Load (TMDL) Waste Load Allocations (WLA) which would reduce nitrogen inputs from wastewater treatment plants by 58.5% over 15 years from the early 1990s baseline, a reduction of 42 million pounds per year. As of 2016, both the New York and Connecticut nitrogen loads were below the Waste Load Allocations permitted by the 2000 TMDL for the first time, thus achieving this major goal. 

Have these major nitrogen reductions improved the condition of Long Island Sound, particularly the bottom water oxygen depletion or hypoxia? While the duration of hypoxia has remained  unchanged at 56 days

The area of Long Island Sound that becomes hypoxic (low oxygen concentrations) in the summer has decreased by 34 percent since the 1990s, based on the five-year running average. Credit: Long Island Sound Study

both before and after the TMDL, there has been a 34% reduction in the area of hypoxia compared to the pre-TMDL baseline. The most recent five-year running average of the hypoxic area of Long Island Sound was 138 square miles. This is despite a record warm year in 2016, as well as another warm year in 2012, which likely increased hypoxia.  Therefore, major decreases in nitrogen loading to Long Island Sound appear to be significantly reducing the area of hypoxia, addressing another major goal of the Long Island Sound Study.Note: For more information, including an explanation on how the TMDL uses trade-equalized loads to determine the impact of nitrogen discharges based on location visit the environmental indicator section of the Long Island Sound Study website.


This article was written by James Ammerman, Phd, the science coordinator for the Long Island Sound Study.

Please complete your newsletter signup.