New England WSC scientist calibrating a continuous water quality monitor at 410606073245700, Norwalk River at the Norwalk Aquarium.
Continuous Water Quality Monitoring in the Norwalk River Estuary
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By New England Water Science Center
June 20, 2024
The U.S. Geological Survey (USGS), in cooperation with the U.S. Environmental Protection Agency Long Island Sound Study (LISS), is investigating how excess nutrients and low dissolved oxygen affect the water-quality of the lower portion of the Norwalk River Harbor.
This monitoring effort provides natural resource managers with a baseline water-quality dataset in the Norwalk Harbor and how the water quality changes seasonally. Also, the data informs managers how often and how long periods of low-to-no dissolved oxygen occur in the harbor.
Some estuaries in the Long Island Sound show the effects of coastal eutrophication, a process that occurs when water contains a high volume of nutrients. Eutrophication includes the excessive growth of macroalgae and phytoplankton, low dissolved oxygen levels (hypoxia), and deteriorated substrates. These effects degrade the estuarine ecosystem and can lead to fish kills and produce harmful toxins. An overabundance of nutrients also contributes to the loss of eelgrass, which provides important underwater habitat and was once commonly found in every bay and harbor in Long Island Sound (Vaudrey and others, 2013). Historically, areas in the Long Island Sound suffer from the effects of eutrophication, with near-zero dissolved oxygen levels recorded in the Norwalk Harbor on multiple occasions.
The Norwalk watershed is 64-square miles and has a mixed land use, being primarily forested in the northern portion and heavily urbanized in the southern portion. There are multiple point and nonpoint sources of nutrients into the system with four major wastewater treatment plants located along the main stem of the Norwalk River and septic systems located throughout the watershed.
Sources/Usage: Public Domain. View Media Details
Sources/Usage: Public Domain. View Media Details
The USGS began operating a continuous water quality monitoring station on the Norwalk River Harbor at the Maritime Aquarium at Norwalk in the spring of 2021 as part of a larger project to look at water-quality of select Long Island Sound estuaries.
This monitoring station is equipped with both near-surface and near-bottom continuous water-quality monitors that collect water temperature, specific conductance, salinity, dissolved oxygen (DO), turbidity and chlorophyll-a and pH at 6-minute intervals. In addition to the continuous water-quality data at this location, continuous ocean elevation data is recorded at 6-minute intervals to monitor for tidal heights. Data from this location is accessible on the web here: Norwalk R at Maritime Aquarium NR S Norwalk, CT - USGS Water Data for the Nation
Sources/Usage: Public Domain. View Media Details
Sources/Usage: Public Domain. View Media Details
Sources/Usage: Public Domain. View Media Details
During the summers of 2021 and 2022, dissolved oxygen concentrations often dropped below 3 milligrams per liter (mg/L) in both the near-surface and near-bottom water, which is the defined limit for DO by the EPA. Data from the monitoring station shows that there are wide-ranging fluctuations in the concentration of DO in the Norwalk Harbor. During daylight hours, algal photosynthesis produces DO and the concentrations in the water have been measured greater than 20 mg/L and greater than 200% saturation. At night, the DO is consumed by the plants and algae in the system through respiration causing the DO levels to often drop below 3.0 mg/l and 1.0 mg/L. The daily change in DO concentrations has a very large range and may cause the habitat to be unsuitable for many sensitive species of fish and invertebrates. These large swings in dissolved oxygen levels identified a need for more monitoring in the estuary. Continued monitoring will help to characterize the frequency of and the drivers behind these large swings in dissolved oxygen.
Sources/Usage: Public Domain. View Media Details
Embayment Monitoring to Support Nutrient Management Activities in Connecticut for Long Island Sound
The USGS, in cooperation with the Connecticut Department of Energy and Environmental Protection will be collecting water-quality and hydrologic data at four embayments from April 2021 to March 2025: Mystic, Norwalk, Saugatuck, Sasco-Southport complex, and Farm.
Calibrating a continuous water quality monitor
New England WSC scientist calibrating a continuous water quality monitor at 410606073245700, Norwalk River at the Norwalk Aquarium.
Collecting a Water Quality sample
New England WSC hydrologic technicians collect a Water Quality sample at 410606073245700 location, Norwalk River at the Norwalk Aquarium.
New England WSC hydrologic technicians collect a Water Quality sample at 410606073245700 location, Norwalk River at the Norwalk Aquarium.
Inspecting the water quality monitoring equipment
New England WSC hydrologic technician inspecting the continuous water quality monitoring equipment deployed at 410606073245700, Norwalk River at the Norwalk Aquarium.
New England WSC hydrologic technician inspecting the continuous water quality monitoring equipment deployed at 410606073245700, Norwalk River at the Norwalk Aquarium.
Inspecting the gage equipment
New England WSC hydrologic technician inspecting the gage equipment at 410606073245700, Norwalk River at the Norwalk Aquarium.
New England WSC hydrologic technician inspecting the gage equipment at 410606073245700, Norwalk River at the Norwalk Aquarium.
Continuous water quality gaging station
Continuous water quality gaging station located at Norwalk River at Norwalk Aquarium near South Norwalk, Connecticut (USGS site ID 410606073245700)
Continuous water quality gaging station located at Norwalk River at Norwalk Aquarium near South Norwalk, Connecticut (USGS site ID 410606073245700)
Inspecting continuous water quality monitoring equipment
New England WSC scientists inspecting the continuous water quality monitoring equipment deployed at 410606073245700, Norwalk River at the Norwalk Aquarium.
New England WSC scientists inspecting the continuous water quality monitoring equipment deployed at 410606073245700, Norwalk River at the Norwalk Aquarium.
The U.S. Geological Survey (USGS), in cooperation with the U.S. Environmental Protection Agency Long Island Sound Study (LISS), is investigating how excess nutrients and low dissolved oxygen affect the water-quality of the lower portion of the Norwalk River Harbor.
This monitoring effort provides natural resource managers with a baseline water-quality dataset in the Norwalk Harbor and how the water quality changes seasonally. Also, the data informs managers how often and how long periods of low-to-no dissolved oxygen occur in the harbor.
Some estuaries in the Long Island Sound show the effects of coastal eutrophication, a process that occurs when water contains a high volume of nutrients. Eutrophication includes the excessive growth of macroalgae and phytoplankton, low dissolved oxygen levels (hypoxia), and deteriorated substrates. These effects degrade the estuarine ecosystem and can lead to fish kills and produce harmful toxins. An overabundance of nutrients also contributes to the loss of eelgrass, which provides important underwater habitat and was once commonly found in every bay and harbor in Long Island Sound (Vaudrey and others, 2013). Historically, areas in the Long Island Sound suffer from the effects of eutrophication, with near-zero dissolved oxygen levels recorded in the Norwalk Harbor on multiple occasions.
The Norwalk watershed is 64-square miles and has a mixed land use, being primarily forested in the northern portion and heavily urbanized in the southern portion. There are multiple point and nonpoint sources of nutrients into the system with four major wastewater treatment plants located along the main stem of the Norwalk River and septic systems located throughout the watershed.
Sources/Usage: Public Domain. View Media Details
Sources/Usage: Public Domain. View Media Details
The USGS began operating a continuous water quality monitoring station on the Norwalk River Harbor at the Maritime Aquarium at Norwalk in the spring of 2021 as part of a larger project to look at water-quality of select Long Island Sound estuaries.
This monitoring station is equipped with both near-surface and near-bottom continuous water-quality monitors that collect water temperature, specific conductance, salinity, dissolved oxygen (DO), turbidity and chlorophyll-a and pH at 6-minute intervals. In addition to the continuous water-quality data at this location, continuous ocean elevation data is recorded at 6-minute intervals to monitor for tidal heights. Data from this location is accessible on the web here: Norwalk R at Maritime Aquarium NR S Norwalk, CT - USGS Water Data for the Nation
Sources/Usage: Public Domain. View Media Details
Sources/Usage: Public Domain. View Media Details
Sources/Usage: Public Domain. View Media Details
During the summers of 2021 and 2022, dissolved oxygen concentrations often dropped below 3 milligrams per liter (mg/L) in both the near-surface and near-bottom water, which is the defined limit for DO by the EPA. Data from the monitoring station shows that there are wide-ranging fluctuations in the concentration of DO in the Norwalk Harbor. During daylight hours, algal photosynthesis produces DO and the concentrations in the water have been measured greater than 20 mg/L and greater than 200% saturation. At night, the DO is consumed by the plants and algae in the system through respiration causing the DO levels to often drop below 3.0 mg/l and 1.0 mg/L. The daily change in DO concentrations has a very large range and may cause the habitat to be unsuitable for many sensitive species of fish and invertebrates. These large swings in dissolved oxygen levels identified a need for more monitoring in the estuary. Continued monitoring will help to characterize the frequency of and the drivers behind these large swings in dissolved oxygen.
Sources/Usage: Public Domain. View Media Details
Embayment Monitoring to Support Nutrient Management Activities in Connecticut for Long Island Sound
The USGS, in cooperation with the Connecticut Department of Energy and Environmental Protection will be collecting water-quality and hydrologic data at four embayments from April 2021 to March 2025: Mystic, Norwalk, Saugatuck, Sasco-Southport complex, and Farm.
Calibrating a continuous water quality monitor
New England WSC scientist calibrating a continuous water quality monitor at 410606073245700, Norwalk River at the Norwalk Aquarium.
New England WSC scientist calibrating a continuous water quality monitor at 410606073245700, Norwalk River at the Norwalk Aquarium.
Collecting a Water Quality sample
New England WSC hydrologic technicians collect a Water Quality sample at 410606073245700 location, Norwalk River at the Norwalk Aquarium.
New England WSC hydrologic technicians collect a Water Quality sample at 410606073245700 location, Norwalk River at the Norwalk Aquarium.
Inspecting the water quality monitoring equipment
New England WSC hydrologic technician inspecting the continuous water quality monitoring equipment deployed at 410606073245700, Norwalk River at the Norwalk Aquarium.
New England WSC hydrologic technician inspecting the continuous water quality monitoring equipment deployed at 410606073245700, Norwalk River at the Norwalk Aquarium.
Inspecting the gage equipment
New England WSC hydrologic technician inspecting the gage equipment at 410606073245700, Norwalk River at the Norwalk Aquarium.
New England WSC hydrologic technician inspecting the gage equipment at 410606073245700, Norwalk River at the Norwalk Aquarium.
Continuous water quality gaging station
Continuous water quality gaging station located at Norwalk River at Norwalk Aquarium near South Norwalk, Connecticut (USGS site ID 410606073245700)
Continuous water quality gaging station located at Norwalk River at Norwalk Aquarium near South Norwalk, Connecticut (USGS site ID 410606073245700)
Inspecting continuous water quality monitoring equipment
New England WSC scientists inspecting the continuous water quality monitoring equipment deployed at 410606073245700, Norwalk River at the Norwalk Aquarium.
New England WSC scientists inspecting the continuous water quality monitoring equipment deployed at 410606073245700, Norwalk River at the Norwalk Aquarium.