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Science Resources

In these times of “alternative facts,” this section will tell you how we know Long Island waters are in trouble, and why we are confident that improving wastewater treatment and reducing fertilizer usage will go a long way to solving the problems.

FACT:  Long Island’s water pollution problems are primarily caused by sources that the federal Clean Water Act left to state and local governments to regulate.

The Clean Water Act does not directly regulate cesspools/septic systems and fertilizer, the biggest local contributors to Long Island’s nitrogen crisis.  

Today, innovative/alternative onsite septic systems, together with increased understanding of how land use affects water quality, provide an unprecedented opportunity to address threats to Long Island’s drinking water and the lakes, streams, bays and harbors that define what it is to be a Long Islander.   Among other actions, the Long Island Clean Water Partnership has been working at the state, county and town level to gain approval of the new systems and funding to make them affordable to homeowners.

Much of this work is being coordinated under the umbrella of the Long Island Nitrogen Action Plan, funding for which the Partnership helped obtain.  For more information on the Plan, see http://www.dec.ny.gov/lands/103654.html.

Below, we provide additional resources for the curious. 

Human Health

  1. Drinking Water

    FACT:  Long Island’s drinking water comes from a large underground aquifer, not rivers or reservoirs.  According to the Suffolk County Water Authority (SCWA),“Almost 70 percent of Suffolk County community supply wells were rated as high, or very high, for susceptibility to nitrate” in a 1999 assessment.  http://s1091480.instanturl.net/dwqr2016/pages/page-2-3.pdf

    What does that mean for the health of you and your family?

    Nitrate is a bio-available form of nitrogen, which is converted to nitrite in the human body.  Excess nitrite can interfere with the blood’s ability to carry oxygen, especially dangerous for infants (blue baby syndrome).  The federal drinking water standard is 10ppm (or 10 mg/L), and the SCWA warns that “Because the effects of nitrate and nitrite are additive, water containing more than 10 mg/L of total nitrate/nitrite should not be used to prepare infant formula or other beverages for infants.” http://s1091480.instanturl.net/dwqr2016/pages/page-12-22.pdf

    For adults, most of the health problems associated with excess nitrogen arise from toxic algae produced by the nitrogen (see below), though some studies have found direct links between excess nitrogen and disease.

    If water is piped to your home or business by the SCWA or a Nassau County supplier, the water has been treated or blended to comply with federal drinking water standards, though you may want to test the nitrate level if there is an infant in the house. 

    However, no blending or treating occurs in water drawn from private wells which serve 200,000 people in Suffolk.  Ten percent of such wells were found by Suffolk County to exceed the federal drinking water standard for nitrogen.  It is a good idea to have your well-water tested.  See http://suffolkcountyny.gov/Departments/HealthServices/EnvironmentalQuality/WaterResources/PrivateWellWaterTestingProgram.aspx.

    Even if your water currently complies with federal standards, there are numerous reasons to be concerned about protection of the aquifer.  First, some pollutants of emerging concern are not treated by water suppliers, such as pharmaceutical and personal care products.  Second, the more treatment and blending that suppliers need to do, the more costly water will become.  It is also costly for water suppliers to replace supply wells when the raw water they draw becomes too polluted to treat.  Third, Nassau County is already experiencing problems with water quantity as well as quality, and this concern is beginning to spread to Suffolk County.

  2. Surface Waters

FACT:  Toxic algae fueled by excess nitrogen pose a range of health threats to humans.

The most dangerous forms of algae are certain strains of cyanobacteria, the presence of which caused closures of numerous lakes and ponds across Long Island in the past three summers. Breathing nearby air can cause asthma and possibly Lou Gehrig’s disease (this research is ongoing); contact can cause rashes and allergic symptoms such as eye irritation, nasal discharge and swollen lips; swallowing cyanobacteria can cause nausea and diarrhea.  In other places, there have been reports of kidney damage, heart failure and death from underwater play in affected waters. On Long Island, no humans are known to have died, but a dog’s death is attributed to cyanobacteria in the Town of East Hampton.

Eating shellfish tainted by toxic algae can also cause disease.

Aside from health and recreational impacts on humans, excess nitrogen poses numerous threats to marine life.  Below is a summary of leading studies on this issue affecting Long Island’s three main estuaries:  Great South Bay, Peconic Bay, and Long Island Sound. 

Great South Bay

Studies beginning in 2008 opened people’s eyes to cesspools and conventional septic systems as the main source of Great South Bay’s debilitating algae blooms.  Until these studies, stormwater runoff was presumed to be the largest water quality concern.  Instead, the studies’ authors found that “wastewater is the dominant source of nitrogen to Great South Bay, particularly wastewater from septic systems,” which accounted for 67% of the total land-derived nitrogen load to Great South Bay.  (2011 report, page 4)

Kinney, E. L. and I. Valiela. 2011. Nitrogen loading to Great South Bay: Land use, sources, retention, and transport from land to Bay. Journal of Coastal Research 27: 672-686. http://www.jcronline.org/doi/abs/10.2112/JCOASTRES-D-09-00098.1

Kinney, E. L. and I. Valiela. 2011. Nitrogen loading to Great South Bay: Report on Phase 2 Management Scenarios. Report to the NY State Department of State Division of Coastal Resources and The Nature Conservancy.  http://easterndivision.s3.amazonaws.com/Marine/Kinney_Valiela_Nitrogen_to_GSB_PhaseII_Report_2011.pdf

Phase 1 report:


Excess nitrogen, acting through algae blooms, causes low dissolved oxygen, which can kill fish and shellfish and cause dead zones. In 2015 and 2016, the United States Geological Survey and The Nature Conservancy documented that dissolved oxygen dropped below 3.0mg/L numerous times in Great South Bay even though New York law states that “the DO concentration shall not fall below the acute standard of 3.0 mg/L at any time.”  https://govt.westlaw.com/nycrr/Document/I4ed90412cd1711dda432a117e6e0f345?viewType=FullText&originationContext=documenttoc&transitionType=CategoryPageItem&contextData=(sc.Default)

Peconic Estuary

Total Maximum Daily Load (TMDL) for Nitrogen in the Peconic Estuary, 2007

In 2007, local governments proposed to reduce nitrogen and its adverse impacts on marine life in the Peconic Estuary by setting reduction targets. However, the means for reducing nonpoint sources was not clearly specified, and the pledges were not mandatory.    


Peconic Estuary TMDL Review, U.S. EPA, January 22, 2013

Five years after the above promises, the U.S. Environmental Protection Agency (EPA) found that little progress had been made.  The EPA faulted the TMDL for not including “detailed information on nonpoint source loads for particular sources or land use activities,” and recommended that “[a]ny future modeling efforts should specify loads from particular sources or land use activities.”  


Nitrogen Load Modeling, 2014

Addressing the EPA’s recommendation, The Nature Conservancy applied the methodology used in the Great South Bay studies to the Peconic Estuary. Of land-based sources, wastewater was found to be the largest single contributor of nitrogen (43%), followed by fertilizer (26.4%) and atmospheric deposition (24%). As in Great South Bay, wastewater from residential on-site septic systems and cesspools was found to be the largest contributor of nitrogen in most areas.


Long Island Sound

A Total Maximum Daily Load Analysis to Achieve Water Quality Standards for Dissolved

Oxygen in Long Island Sound, 2000

In this TMDL, governmental agencies proposed to reduce nitrogen in Long Island Sound by 58.5% by August 2014.  Through direct federal regulation of point sources, most sewage treatment plants in Connecticut and New York upgraded their processes to remove greater quantities of nitrogen.  http://www.dec.ny.gov/docs/water_pdf/tmdllis.pdf

The upgrades led to improvements in the open water parts of the Sound:  hypoxia (low dissolved oxygen) affected 87 square miles in 2014, compared to a peak of 393 square miles in 1994. http://longislandsoundstudy.net/indicator/area-of-hypoxia/  However, the extent of hypoxia can vary greatly from year to year depending on weather, and closer to shore, excess nitrogen and low dissolved oxygen were still making it difficult for marine life to survive.

Attention shifted to nonpoint sources of nitrogen, such as cesspools, septic systems, and fertilizer.  Important modeling was performed on the Long Island and Connecticut sides of the Sound.  In December 2015 the EPA announced a new “strategy” to work with Connecticut, New York and NGOs to focus on specific problem watersheds.  These efforts are ongoing.

Tidal Wetlands

Coastal eutrophication as a driver of salt marsh loss, Nature, Vol. 490 (2011)

In a widely cited article based on nine years of field studies, Linda A. Deegan and other scientists found that excess nitrogen “can be a driver of salt marsh loss.”  This is important not only for the multiple species that depend on salt marshes at some point during their life cycles, but also important for humans as wetlands protect communities from storm surges. 



Like scallops?  Then you should care about eelgrass, scallops’ favorite habitat, which is big trouble around Long Island.

Since the 1930s, the extent of underwater eelgrass (Zostera marina) around Long Island has declined from 197,684 acres to 21,802 acres as of 2015.  http://www.dec.ny.gov/docs/fish_marine_pdf/oceanactionplan.pdf (page 17). 

The Southern New England and New York Seagrass Research and Restoration Initiative, a multi-year study led by The Nature Conservancy and funded by NOAA, examined reasons for the eelgrass decline.  Excess nitrogen was found to be the primary culprit.

Phase I report:  The Eelgrass Resource of Southern New England and New York: Science in Support of Management and Restoration Success (2012) http://www.conservationgateway.org/Documents/UNH%20Eelgrass%20Final%20Report%202012.pdf

Phase II report:  Southern New England and New York Seagrass Research Towards Restoration (2014) http://www.conservationgateway.org/ConservationPractices/Marine/HabitatProtectionandRestoration/Pages/Southern-New-England-and-New-York-Seagrass-Research-Initiative.aspx