CEQ: Pollution in Long Island Sound

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Sound + Shore

Pollution in Long Island Sound

{Lates Data No Change}

The amount of nitrogen dumped into Long Island Sound and its tributaries affects oxygen levels in the water. Connecticut has been reducing nitrogen discharges to Long Island Sound and has met all targets to date:

{Trend in Nitrogen Discharges to Long Island Sound}

However, the area of low oxygen expanded again in 2009:

{Trend in Hypoxia}

The area of shellfish beds unconditionally approved for harvesting has declined since 2005:

{Trend in Open Shellfish Beds}

Hypoxia is a condition in the water when oxygen levels are too low to fully support desirable forms of life, including fish and lobsters. (For this indicator, hypoxia is defined as less than or equal to 3.5 mg/l of dissolved oxygen.) Hypoxia occurs when the nitrogen in pollution stimulates excessive growth of aquatic plants, which die and are consumed by oxygen-using bacteria. Connecticut's goal is to “eliminate the adverse impacts of hypoxia resulting from human activities.” Hypoxia occurs predominantly in the western portions of the Sound. Weather greatly influences hypoxia, making year-to-year changes less important than long-term trends.

To reduce the nitrogen inputs that cause hypoxia, Connecticut and New York adopted a comprehensive management plan in 1994, and built upon that plan with an expanded agreement in 2002.

The top graph tracks the amount of nitrogen discharged to the Sound and major rivers by 79 sewage treatment plants, 3 large coastal industrial facilities, and a group of industrial sources in the Naugatuck River watershed. Connecticut’s investments in nitrogen-removal technology have been successful. Also there are large uncontrolled quantities of nitrogen entering Long Island Sound in the rain that runs off lawns and pavement . Overall, Connecticut’s share of the total nitrogen pollution in Long Island Sound is about one-third, and New York’s is two-thirds. In April 2001, the federal Environmental Protection Agency approved the New York and Connecticut joint plan for implementing a Total Maximum Daily Load (TMDL). The TMDL is the maximum amount of pollutants that can be discharged while still allowing water quality standards to be attained.

The Connecticut Department of Agriculture's Bureau of Aquaculture and Laboratory Services monitors shellfish beds and classifies them according to their potential for the harvesting of healthful, uncontaminated shellfish. The third graph above shows the acreage of shellfish beds that are unconditionally approved for harvesting because they are generally unaffected by pollution. (Even areas that are fully approved can be closed as a precaution following exceptional rainfalls of three or more inches.) Aquaculture experts have suggested that the volume of runoff from lawns and pavement is increasing and flowing further into the sound, resulting in the shrinkage of the shellfish beds that are fully approved.

Technical notes: The second graph shows the area of Long Island Sound that had adequate oxygen levels throughout the year. The sampling area (2700 square kilometers) does not include the whole Sound (3400 square kilometers). The areas not sampled are shallow waters (less than two meters deep) near shore, which generally do not experience hypoxia; embayments; the eastern end of the Sound, which is not expected to experience hypoxia; and an area in the far western end, which probably becomes hypoxic in most years. In 2004, the DEP redefined hypoxia to include waters with less than or equal to 3.5 mg/l of dissolved oxygen (replacing the older 3.0 mg/l standard). The areas of adequate oxygen displayed on the graph were then recalculated for all years.

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Pollution in Long Island Sound