2014 Hypoxia Review for Long Island Sound

Long Island Sound’s array of fish and wildlife are put in harm’s way each summer by a low oxygen condition known as hypoxia. Excess nitrogen, mainly from treated sewage, spurs algae blooms which use up dissolved oxygen as they die and decompose. Lack of oxygen can get so bad in the western half of the Sound that it’s extremely detrimental for fish, crustaceans, and other creatures. It is the ecosystem’s most critical ecological problem.

Save the Sound has worked with scores of public, private, and governmental entities to combat this problem. And the good news is that efforts to reduce nitrogen output from sewage plants are starting to yield results.

Every summer state and federal agencies, such as the Connecticut Department of Energy and Environmental Protection, collect tons of data to tell us how Long Island Sound’s waters are coping with nitrogen and hypoxic conditions. They analyze and summarize the oxygen conditions of the Sound’s bottom waters from New Haven and Port Jefferson west to the East River.

Compared to recent years, 2014 was better than average for Long Island Sound. 

How did hypoxia look this summer?
Oxygen levels often start heading downhill in July, but this year there was no sign of hypoxia at that point. Things did look grim in early August, but two weeks later, oxygen levels had increased in the hypoxic areas. September brought pockets of low oxygen between Westchester and Nassau counties, and off New Haven. However, by mid-September, water quality almost everywhere had improved significantly. Typically, dissolved oxygen concentrations drop in July and stay low through September, when water temperatures start to cool.

How does that stack up to previous years?
Here’s a quick look at how this summer compared to last, using the number of square miles affected by low levels of dissolved oxygen. Lower numbers in 2014 are better for the Sound, fish, and wildlife. These maps show how conditions changed throughout the summer.

Number of square miles affected by hypoxia.


What does this mean for wildlife?
graph2Low levels of dissolved oxygen are a proxy for habitat degradation in Long Island Sound. Hypoxia occurs with oxygen levels below 3 mg/L but fish, wildlife, and critical habitat already feel negative effects when levels drop below 4.8mg/l. There is a big difference in fish biomass—the weight of the total amount of fish caught in monthly research trawls by CT DEEP and others—when oxygen levels are below 4.8 mg/L. With this in mind, 4.8mg/L is considered to be protective of everything that lives in the Sound and has been the interim goal the region has strived for over the past two decades.

Why was this summer better than previous years?
A more complete comparison will have to await the annual water quality analysis of the CT DEEP. In the meantime, Save the Sound can offer a couple of preliminary observations and possible explanations for the better conditions this summer.

First, this summer was unusually cool in our region, with a return to “old time” wind conditions. Cooler weather means cooler water, which holds more oxygen. Perhaps more importantly, we enjoyed a lot of cool, clear days with winds out of the northeast, and several days with strong easterly winds. These wind patterns mix the top oxygen-rich waters with oxygen depleted bottom waters, raising oxygen levels throughout the Sound.

Second, we may be beginning to see the benefits of two decades of upgrading the numerous sewage treatment plants in New York and Connecticut. Many of these nitrogen reduction improvements came on line in 2012 and 2013, making this summer one of the first wherein the ecosystem was operating with lower levels of nitrogen input. Limiting nitrogen pollution provides a critical pathway toward bringing back vast schools of fish, clearer waters, and acres of new eel grass habitat critical to spawning even more crabs, fish, and wildlife.

While this summer is an indication of good news, climate change has, unfortunately, been driving overall weather conditions on the Sound in the wrong direction—hotter, stiller summers that cause greater oxygen depletion. Stronger storms associated with climate change can also wash more nitrogen-laden sewage into the Sound. We cannot rely on Mother Nature to control our hypoxia woes as a long-term strategy.

We must continue the enormously challenging effort to pull excess nitrogen out of the system. Much more is needed to restore the Sound to a healthy balance. That is why Save the Sound is spearheading a new campaign to stop excess nitrogen from finding its way into Long Island Sound. Stay tuned to hear more about that soon.

How can you join in the effort? Sign the Long Island Sound Pledge today—it has concrete ideas for how you can help heal the Sound, starting in your own backyard!

Posted by Tyler Archer, CFE / Save the Sound
Cover Photo by Abby Archer Photography

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