Embayment Monitoring to Support Nutrient Management Activities in Connecticut for Long Island Sound

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Continuous water quality station on the Mystic River at the Mystic Seaport, Mystic Connecticut (Site ID 412141071580200). Setup includes top and bottom multiparameter sondes and velocity uplooker.

Coastal estuaries in southern New England show the effects of excess nutrients and coastal eutrophication. The effects of excess nutrients include excessive growth of macroalgae, excessive blooms of phytoplankton, hypoxia and oxygen depletion, and deteriorated substrates. Excessive nutrients also contribute 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; Buzzards Bay National Estuary Program, undated). The state of Connecticut continues to promote a comprehensive approach to managing impacts to Long Island Sound and its coastal embayments and as part of that effort, the Connecticut Department of Energy and Environmental Protection (CT DEEP) seeks to develops monitoring and modeling efforts for selected embayment in LIS.

In 2021, The U.S. Geological Survey (USGS) in collaboration with CT DEEP began collecting water-quality and hydrologic information for two years in each embayment that could be used to inform embayment modeling efforts. Data collection in Norwalk Harbor and Mystic Harbor began in May 2021 and ended in April 2023, and Saugatuck River and Southport Harbor monitoring began in May 2022 and ended in April 2024. The Farm River monitoring began in April 2023 and ended in March 2025. The Poquonnock will be the sixth embayment to be monitored by the USGS in a concerted effort to provide hydrologic- and water-quality data available for CT DEEP’s embayment modeling efforts. The Poquonnock embayment began in July 2025 and will end in June 2027. 

The objectives of the study are to 1) Obtain representative water‐quality data under a range of seasonal conditions to characterize the water-quality spatially and vertically within each embayment. 2) Collect selected water‐quality data with high temporal resolution to provide time‐series data needed for water-quality model calibration and evaluation. 3) Collect water-elevation and velocity data in each embayment to provide additional understanding of physical mixing and variability in the embayment. Nutrient models for each embayment will be created based on the collected data which will help improve the understanding of physical and chemical processes of embayments in Long Island Sound.

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Embayment monitoring sites in Connecticut for Long Island Sound.

Data collection sites

*Previous or ongoing data collection efforts for water quality and/or hydrologic data to support other USGS projects

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