Photos of the Long Island Sound

Research & Monitoring

Status & Trends

LISS Ecosystem Targets and Supporting Indicators

Extent of Hypoxia

Measurably reduce the area of hypoxia in Long Island Sound from pre-2000 Dissolved Oxygen TMDL averages to increase attainment of water quality standards for dissolved oxygen by 2035, as measured by the five-year running average size of the zone.

( Click labels in legend to hide data and adjust scale )
Progress
Area in Square Miles
YearArea of
Hypoxia
Five-year Running
Average
1987309
1988251
1989328
1990174
1991122237
199280191
1993202181
1994393194
1995305220
1996220240
199730230
1998168223
1999121169
2000173142
2001133125
2002130145
2003345180
2004202197
2005177197
2006199211
2007162217
2008180184
2009169177
2010101162
2011130148
2012288174
201380154
201487137
201538125
2016197138
20177095
20185289

Status and Trends

Meeting the ecosystem target (measured as the maximum area of bottom waters with dissolved oxygen ≤ 3 mg/L) is ahead of schedule. The five-year running average of the hypoxic area of Long Island Sound (2014-2018) is 89  square miles compared to an average of 208 square miles from 1987-2000. This is a 57 percent reduction from the pre-2000 Total Maximum Daily Load (TMDL) average hypoxic area. Based on the last 20 years of interannual variability, a 28 percent reduction is necessary to achieve a measurable reduction (see data note). Further reductions in the area of hypoxia are needed in order to fully attain water quality standards for dissolved oxygen.

As shown in the chart above, there is considerable annual variability in the maximum area of hypoxic waters, in part due to annual variations in weather (temperature, wind, rainfall, etc.).

While the area of hypoxia has been reduced compared to the pre-TMDL baseline, the duration of hypoxia has remained unchanged at 56 days compared to the pre-TMDL baseline (see duration of hypoxia, supporting indicator, 1987-2017).

Challenges

Warming water temperatures will reduce the amount of oxygen that the water can contain, making it more difficult to meet the target long term. In addition to weather variables affecting the area of hypoxia year to year, longer term climate influences will affect the vulnerability of the Sound to hypoxia. Improvements in monitoring, including increased monitoring in embayments, will better define areas affected by hypoxia, and the factors contributing to it.

How is This Target Measured?

Routine monitoring of bottom water hypoxia is done monthly throughout the year and biweekly in the summer by the Connecticut Department of Energy and Environmental Protection (CTDEEP).

Additional summer weekly monitoring is conducted by the Interstate Environmental Commission in Western Long Island Sound. Five buoys of the Long Island Sound Integrated Coastal Observing System (LISICOS) also span the Sound, with bottom water oxygen sensors on the western three buoys. Therefore is good information on both the area and duration of hypoxia, with monitoring data going back to 1987 (conducted by University of Connecticut from 1987-1990, and CTDEEP since 1991).

Bottom hypoxia is measured by lowering instruments with multiple sensors (including dissolved oxygen) through the water column from a research vessel or smaller boat.

Importance

Hypoxia, a deficiency in the amount of oxygen in the water, can be harmful or lethal to fish, invertebrates, and other animals and therefore decrease or eliminate them from Long Island Sound.  

Hypoxia may also limit the growth of animals that are exposed but not killed.

Contact

Dr. James Ammerman, Long Island Sound Study james.ammerman@longislandsoundstudy.net

Source of Data

CTDEEP (primary data source), also the Interstate Environmental Commission for Western Long Island Sound, and LISICOS.

 

Data Notes

  • The technical explanation on how the target was selected is found in Appendix B of the Comprehensive Conservation and Management Plan.

 

 

 

 

 

 

 

 

 

 

 

 

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Related Ecosystem Targets

Did You Know?

Hypoxia is more frequent in the Western Sound.

Learn More


2017 Long Island Sound Hypoxia Season Review



 

 

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