Photos of the Long Island Sound

Status and Trends: LISS Environmental Indicators

Type of Indicators: Health/Condition Response/Performance Socio-Economic Historical/Background

Water Quality

Water quality indicators are divided into four categories, each of which has been identified by the program as a priority area of concern. The categories include hypoxia (low dissolved oxygen) and nutrients; toxic contaminants; pathogens; and floatable debris. These indicators help resource managers assess recent and historical water quality trends, and management efforts to improve conditions.

Hypoxia and Nutrients

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Area of Hypoxia

Hypoxia is a condition that occurs in bodies of water as dissolved oxygen concentrations decrease to levels where organisms become physically stressed and ultimately cannot survive. The area of hypoxia in Long Island Sound refers to the number of square miles in which dissolved oxygen concentrations were less than 3 mg/L over the course of a single year. View Indicator

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Duration of Hypoxia

Hypoxia is a condition that occurs in bodies of water as dissolved oxygen concentrations decrease to levels where organisms become physically stressed and ultimately cannot survive. Duration of hypoxia refers to the number of days in a year during which hypoxia was observed in Long Island Sound. View Indicator

Frequency of hypoxia

Frequency of Hypoxia

This map illustrates the frequency of occurrence of hypoxia in LIS bottom waters over the last two decades. It indicates what areas of Long Island Sound experience hypoxic conditions most often, and which are rarely affected. View Indicator

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LIS Point Source Nitrogen-Trade Equalized Loads

This measure indicates the management effort to reduce nitrogen from wastewater treatment plants in order to meet state and federal water quality standards. View Indicator

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Chlorophyll a Concentration

Chlorophyll a is the green pigment in plants, and the concentration in surface water is an indicator of the amount of microscopic plants (called phytoplankton). This indicator is intended to characterize the spring phytoplankton bloom conditions in the western Sound each year. View Indicator

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Water Quality Index

The water quality index is a calculation that combines several water quality measurements to rate overall water quality in Long Island Sound on an annual basis. View Indicator

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Sediment Delta 15N

Delta 15N is a nitrogen isotope whose relative abundance in benthic sediment is used to determine the contribution of wastewater and sewage to total nitrogen. View Indicator

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Increases in Population and Sewage

Clostridium perfringens, a bacterial spore found in sediments, is an indicator of sewage inputs and can be used to create a historical record of the magnitude of sewage input to the Sound. View Indicator

Sediment Organic Carbon Concentration Chart

Sediment Organic Carbon Concentration

Measurements of organic carbon concentration in sediment cores can be used to reconstruct a historical record of organic carbon in Long Island Sound. View Indicator

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Sediment Delta 13C

δ13C is an isotope of carbon used as a proxy for hypoxia in this indicator, enabling the creation of a 1000-year historical record of bottom water conditions in Long Island Sound. View Indicator

Toxic Contaminants

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Industrial Chemical Discharges (TRI data – CT and NY)

This indicator compiles the total amount of discharges of toxic chemicals manufactured and used at industrial facilities that are released into the Sound either by air or by water. View Indicator

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Wastewater Treatment Plants Meeting Toxicity Standards

Aquatic organisms are exposed to effluent from wastewater treatment facilities as a test for effluent toxicity. This indicator is the percentage of facilities in CT passing these tests. View Indicator

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Contaminant Trends in Mussel Watch Sites

Mussels tend to stay in one location and feed by filtering particles out of the surrounding water. They can accumulate local contaminants such as metals and PCBs in their tissues. Measuring levels of contaminants in their tissue is a good indicator of local contamination. View Indicator

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Sediment Quality Index

This index indicates the extent and severity of contaminants such as PCBs, hydrocarbons, metals, and pesticides in seafloor sediments throughout Long Island Sound. View Indicator

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Heavy Metals in Sediment

Sediment cores were sampled near Norwalk Harbor to determine the historic trends of toxic contamination in the seafloor sediment of the Sound. The cores give a record of metal contamination from the pre-colonial period to the post-industrial era. View Indicator

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Lead Concentrations in Sediment by Basin

This map shows the concentration of the heavy metal lead within the seafloor sediments throughout Long Island Sound. View Indicator

Pathogens

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Approved Shellfish Acreage

This measure indicates whether water quality conditions in tidal rivers and coastal waters can support recreational and commercial shellfishing of oysters and clams. View Indicator

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No Discharge Area

Areas designated as "no discharge zones" prohibit the release of sewage from any vessels. Sewage can damage habitats and be a major source of pathogens to the coastal environment. This map shows the areas in Long Island Sound designated as No Discharge Zones. View Indicator

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Vessel Pump-out Stations

Vessel pump-out stations remove sewage from vessel holding tanks for onshore treatment. Their widespread availability is important to reducing the release of sewage by vessels into the Sound. This indicator reports the increased number of vessel pump-out stations in both states over the last 15 years. View Indicator

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Beach Closures and Advisories

Beaches are closed when high abundances of pathogens (bacteria or viruses) are detected or when heavy rainfall results in a high risk of increased pathogens. A large number of beach closure days can be an indicator of a problem with pathogen contamination or of an unusually wet year. View Indicator

Floatable Debris

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Floatable Debris (NYC)

This measure indicates the effort to collect floatable debris in western Long Island Sound. View Indicator

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Beach Debris Collected

This measure indicates the efforts of volunteers to clean debris deposited on Long Island Sound beaches. View Indicator

 
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