Municipal Actions to Reduce Harmful Hypoxia in Long Island Sound

The TRBP Floating Workshop IX took place on June 12, 2009.  It was planned to coordinate with and compliment The Last Green Valley's Source to Sea, Connecting the Drops in The Last Green Valley events.  It featured a tour of the Thames River aboard Project Oceanology's Envirolab and focused on upland contributions of nitrates to the waters of Long Island Sound. Click here to view a slide show of the workshop.

Nitrates are the leading cause of seasonal hypoxic conditions in Norwich Harbor, part of the Thames River estuary and in western Long Island Sound. There are actions municipalities can take to reduce the upland contribution of nitrates.  Select examples were featured on the Thames River tour.    The complete workshop agenda was developed based on the results of a Municipal Survey conducted in 2009.   

Long Island Sound is an estuary, or a place where freshwater from land runoff combines with sea water in a semi-enclosed area.  Estuaries are normally highly productive habitats.  However, in parts of Long Island Sound and in Norwich Harbor, seasonal hypoxia (low dissolved oxygen) in deep water habitats place stress on marine organisms.   Swimming organisms, such as fish, can leave the area.  Bottom dwelling organisms, such as shellfish and marine worms, may be stressed or killed due to the lack of available oxygen. 

The major cause of hypoxia in Long Island Sound is nutrient enrichment, especially in the form of nitrates.  Near the surface, where solar exposure is high, phytoplankton thrive in the nutrient enriched water.   Upon death, they settle to the bottom where they are decomposed by oxygen consuming decomposer organisms.   Once the dissolved oxygen concentrations fall below 5 mg/l, mild adverse ecological effects in the bottom water habitats of the Sound begin to occur. According to the Long Island Sound Study the most severe effects (such as mortality) occur when dissolved oxygen levels fall below 1.5 mg/l at any time and below 3.5 mg/l in the short-term (i.e., 4 days).

The major sources of nitrates to surface waters in Connecticut are:

• waste water treatment plant effluent

• atmospheric deposition

• stormwater runoff 

The States of Connecticut and New York are cooperatively working to achieve a Total Maximum Daily Load for nitrates in order to meet water quality standards and improved habitat quality in Long Island Sound.

This workshop was funded in part by the National Fish and Wildlife Foundation as part of the Long Island Sound Study.