As the glacier retreated to the north shore of Long Island Sound between 17,000 and 18,000 years ago, Long Island Sound was filled by a fresh water lake, Glacial Lake Connecticut. The lake was fed by the melt waters from the glacier which were dammed by the Harbor Hill - Roanoke Point - Charlestown Moraines along the north shore of Long Island and continuing across to Rhode Island (see map). This lake drained to the east just west of Fishers Island, at The Race, into Block Island Sound. Block Island Sound was also filled with a fresh water lake. Water level fell in Glacial Lake Connecticut as the spillway near Fishers Island eroded deeper. By about 15,500 years ago Glacial Lake Connecticut was completely drained. With the continued rise in sea level the sound began to be flooded at its lowest levels with sea water. The extent of the flooding varied due to changes in the rate of sea level rise and the rebounding of the land surface due to the unloading of the glacier. Tidal currents now dominate erosion and reworking of the sediments on the floor of the sound. 

            Present day Long Island Sound is an estuary, a place where fresh and marine waters mix. There are now two connections to the sea, one on the western and one on the eastern end. Most of the fresh water comes from the Housatonic, Connecticut and Thames Rivers draining from the north across Connecticut. Less freshwater comes from drainage of portions of New York City, Westchester and Long Island. Due to the large populations living around the sound and the associated development, the Sound has undergone serious degradation. The degradation includes hypoxia (low dissolved oxygen levels), the development and pollution of wetlands and intertidal areas, and the contamination of bay and harbor bottoms with toxic chemicals. Pathogens and toxic chemicals in the water are making sea food unsafe to eat and necessitating the closing of beaches for swimming.

            The most serious immediate problem is hypoxia. If the dissolved oxygen is less than 5 milligrams/liter this begins to affect life in the water, particularly for bottom dwelling organisms. If the level falls below 3.5 milligrams/liter for periods of days many organisms die. If the level falls below 1.5 milligram/liter for any period of time most organisms die. During the late summer large areas of the Sound have dissolved oxygen levels less than 5 milligrams/liter (see map). The tidal range in Long Island Sound is quite large and as a result the sound exchanges water with the ocean relatively rapidly. However, in the western half of the sound the large population in New York City, Long Island and Connecticut discharges large volumes of nutrient enriched sewage into the sound, because most of the sewage has not undergone tertiary treatment. These nutrients encourage the growth of marine plants. When the plants die they sink to the the bottom using up oxygen as they decay. As a result there is a severe depletion in the numbers of fish and shellfish in the waters of the western Sound. The fish and shellfish were and still are important resources that were harvested both commercially and recreationally.

            It is estimated that about $5 billion is generated annually in the regional economy from boating, commercial and sport fishing, swimming and beach going. While the Sound has demonstrable economic value, its aesthetic value as a natural resource is also dependent on the quality of its water and surrounding natural habitats. The clean water act has led to improvements in pollution control and water quality. Wetlands are now protected. Connecticut and New York are committed to building sewage treatment plants, to control industrial discharges and there is an awareness of the dangers of nonpoint source pollution.  Without these efforts the Sound would be in far worse shape than it is.

Estuaries - Extremely productive regions that are a mixture of salt and fresh water.

Long Island Sound is a mixture of fresh water (mainly from the various Connecticut rivers) and salt water (from the Atlantic Ocean). As such, it is an estuary, even
     though it doesn't fit the typical image of an estuary as a flooded river mouth.
     -About 10% of the water in the sound gets exchanged every day (or, in other terms, the
     residence time of the water in the sound is 10 days).
     -Various human activities (such as the pumping of sewage into the sound) result in the
     degradation of the water in Long Island Sound.

Types of Degradation of Long Island Sound

     -Hypoxia - Low dissolved oxygen levels.
     -Development and pollution of wetlands in intertidal areas.
     -Contamination of the bay and harbor bottoms with toxic chemicals.
     -Pathogens and toxic chemicals are making seafood unsafe to eat, and necessitating the
     closing of beaches for swimming.
     -The pollution and destruction of spawning grounds, as well as over fishing, are reducing
     catch.

Hypoxia

     Even under natural conditions, hypoxia was a problem due to the addition of nitrogen from
     natural sources to the sound. This problem is worse under present conditions.

Amounts of nitrogen added to the Sound

Eutrophication

     -Nitrates encourage the growth of algae.
    - During the spring, algae grows in abundance.
     -In the summer, algae dies and settle to the bottom in cooler, non-circulating water.
    - The bacteria feed on the dead algae and use up the oxygen.
    - Bottom dwellers are most susceptible to the effects of hypoxia.
     -10 ppm (mg/liter) Oxygen normal.
    - 5 ppm Oxygen begins to affect life. Larvae are particularly vulnerable.
     -3.5 ppm deadly after a few days

Point Source is mainly sewage treatment plants

Non-point source

Septic Tanks

Urban Storm water Runoff
Boats and Marinas
Fertilizers

Delivery Routes of Non-point Sources

Rivers

Groundwater
Atmospheric

                                                          Types of Treatment of sewage Destined for the Sound

Progress on Long Island Sound

1990 Phase I
-freeze Nitrogen Loading

1994 Phase II
-Reduce Nitrogen by 7,550 tons/year by 2006

1997 Phase III
-Reduce total Nitrogen by 34,000 tons/year over next 15 years.
-Cost is $6 to 8 billion
 

Total Point Source Nitrogen loading
 

Year	Nitrogen tons per year
1990	34,000
1998	29,000

However area and duration of hypoxia increased probably due to wet, warm weather

Toxic Chemicals

Long Island Sound is near the top of contaminated waterways. Only NYC, Boston, and Los Angels Harbors are worse. 

70 tons/day of toxic metals and pesticides enter the Sound. The largest source is storm water runoff and sewer pipes. Long Island also has a problem with bacteria content. Some beaches along the north shore of the island are commonly closed due to high bacteria content.

    - All build up in clams and fishes.
    - Heavy metals cause neurological problems.
          Copper
          Lead
          Cadmium
          Zinc
     -Organic Chemicals are carcinogenic
          PCB's
          DDT (pesticide)
          polycyclic aromatic hydrocarbons

How can you reduce contaminants in general?

     -Fertilize lawns only when necessary. Consider alternatives to chemical fertilizer.
     -Use pesticides only when necessary.
          Find alternatives to grass, such as trees and shrubs.
     -Clean up after your pets, and put animal wastes in garden.
     -Pump out septic tank every 2 to 3 years. Reduce water use in house.
     -Make sideways out of brick, wood, and gravel.
     -Wash cars on grass, not on concrete or asphalt driveway.
     - Do not litter!

Successes

• In 1998, the LISS adopted a 58.5 percent reduction target for nitrogen loads from human sources to the Sound by 2014, with interim five- and ten-year targets to assure steady progress.

• In 2001, the EPA approved Connecticut’s and New York’s plan, called a Total Maximum Daily Load (TMDL), for achieving the reductions and allocating responsibility among nitrogen sources.

• As of  2006, upgrades to sewage treatment plants have decreased nitrogen discharges to the Sound by 40,645 pounds per day since 1994.

• The severity of hypoxia (lack of oxygen) has decreased in the Sound since the late 1980s.

• Toxic industrial chemical releases in the Sound’s watershed have declined 80 percent since 1988.

• Levels of copper, nickel, lead, and zinc as well as many organic compounds have declined in the monitored harbors of the Sound.

• About 600 acres of tidal wetland habitat have been restored in Connecticut and New York  Additional restoration projects are under way in both states.

• As of 2006 100 miles of river migratory corridors have been restored for anadromous fish passage by installing fish ladders and removing

Challenges

• Both Connecticut and New York have committed millions of dollars to upgrade sewage treatment plants, control polluted runoff, and restore habitat, but more is needed.

• A die-off of lobsters that began in mid-September 1999, most severely in the western Sound, has greatly reduced the harvest. Disease outbreaks have hurt both the lobster and oyster fisheries.

• Bluefish, winter flounder, and tautog (black fish) stocks still remain far below the long-term average and have not yet responded to more stringent fishery management measures that were recently implemented.

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