The Long Island Sound Comprehensive
Conservation and Management Plan (CCMP) identifies low dissolved oxygen, or hypoxia, as
the most serious water quality impairment in the Sound. The annual summertime occurrence
of hypoxia in the deeper waters of western Long Island Sound reduces the amount of healthy
habitat necessary to support fish and shellfish. The CCMP identifies excessive discharges
of nitrogen, a nutrient, as the primary cause of hypoxia, and sewage treatment plants as
the primary source of this excess nitrogen. To address this problem, the Long Island Sound
Study (LISS) is implementing a phased approach to reducing nitrogen loads to the Sound
from sewage treatment plants, industrial dischargers, and nonpoint sources. These phased
nitrogen reductions, however, may not raise dissolved oxygen to levels necessary to
support all life stages of marine life in Long Island Sound. Additional measures will
likely be required to achieve the states’ water quality standards for dissolved
oxygen. These measures may include advanced treatment at sewage treatment plants upstream
of the Connecticut border, reductions in atmospheric nitrogen loadings, and several
"non-treatment"techniques, which are the subject of this fact sheet.Solving a large, complex
environmental problem like hypoxia in Long Island Sound requires creative solutions. New
ideas are being considered as part of a dynamic process that takes advantage of changes in
technology and different ways of thinking. This fact sheet highlights some of the methods
other than advanced treatment that have been considered to improve dissolved oxygen levels
in the Sound. Some are more feasible than others, and some may never be implemented. The
alternatives are listed in order, from those most likely to be put in place to the least
likely.
In assessing the alternatives, the
LISS considered the requirements outlined in the federal water pollution control
regulations. The requirements call for the use of treatment over nontreatment techniques
(e.g., increasing the flow of receiving waters to enhance dilution or using in-stream
mechanical aerators to increase oxygen levels). However, non-treatment techniques may be
considered as a
method of
achieving water quality standards on a case-by-case basis when treatment technologies are
not sufficient to achieve the standards.
CREATION OF ARTIFICIAL WETLANDS
Creating artificial wetlands can
provide treatment for storm water runoff entering Long Island Sound. Artificial wetlands,
if well-designed and managed properly, may be able to remove nitrogen from runoff.
However, it is, at best, a partial solution that can be incorporated into the overall
nitrogen control strategy, complementing natural wetland protection and restoration
efforts.
Advantages:
- Provides nitrogen removal;
- May help reduce loadings of toxic
contaminants, sediment, pathogens, and floatable debris by filtering them out before they
reach the Sound; and
- May provide valuable shoreline habitat
for birds and marine life.
Disadvantages:
- Limits public access to the shoreline;
- Presents potential conflicts with
developers; and
- Requires large areas of wetlands to
have a measurable benefit.
AERATION OF BOTTOM WATERS
Locating mechanical aerators in
hypoxia "hot spots" would introduce oxygen to oxygen-depleted waters. Aerators
also would help break up vertical density stratification in the water column, allowing
mixing of oxygen-rich surface waters with oxygen-depleted bottom waters. Although
impractical for large areas,
this
alternative may be considered after planned nitrogen reductions have reduced the areal
extent of hot spots.
Advantages:
- Serves as a direct solution to the low
dissolved oxygen problem;
- Easy to operate;
- Has flexibility and can be used in a
variety of locations;
- Has relatively low capital costs;
- Has proven successful in small scale
operations; and
- Can be switched on and off.
Disadvantages:
- May cause resuspension of sediments
and associated chemical contaminants;
- May disrupt marine organism movement
and migration;
- May eject bacteria and viruses into
the atmosphere;
- Creates froth on the water’s
surface from the bubbles;
- Requires long-term maintenance of
mechanical equipment; and
- Intense energy requirements could
inflate the costs.
SEAWEED FARMS
Raising benthic macro algae
(seaweeds) may help alleviate the hypoxia problem by removing nitrogen from the water
column through biological uptake. As with creation of artificial wetlands, seaweed farms
are at best a partial solution that can be incorporated into an overall nitrogen
management plan.
Advantages:
- Has existing market for seaweed and
its byproducts;
- Removes nutrients from the water
column;
- Generates dissolved oxygen through
photosynthesis; and
- Seaweed farms in other countries have
proven to be successful.
Disadvantages:
- Has limited effectiveness as a single
solution to the hypoxia problem;
- Uncertainty of whether there is
species of seaweed that would be feasible for aquaculture in Long Island Sound; and
- Floating structures may interfere with
navigation.
RELOCATION OF SEWAGE TREATMENT PLANT OUTFALLS
This alternative involves redirecting
New York City sewage treatment plant outfalls from the East River to New York Harbor, and
relocating Westchester County outfalls toward central Long Island. It had been determined
that relocation of the Westchester
County outfalls is not cost-effective. Relocation of the East River
outfalls needs further evaluation.
Advantages:
- Improves dissolved oxygen in western
Long Island Sound and the East River;
- Reduces toxic contaminant loading in
the East River;
- Is cost-effective; and
- May reduce combined sewer overflow
impacts (i.e., nitrogen, toxic contaminants, pathogens, and floatable debris).
Disadvantages:
- Causes adverse water quality impacts
at new discharge locations;
- Introduces new pollutant loads to the
Hudson River circulation pattern;
- Increases nutrients to the New York
Bight and Raritan Bay;
- May cause changes in flora, fauna and
fish migration patterns in the Sound;
- Increases salinity and temperature
alterations in the western Sound;
- May cause adverse effects at Atlantic
Ocean beaches; and
- Disturbs habitat near the diffuser
field at the discharge.
TIDE GATES
Installing tide gates could prevent
tidal currents in the East River from entering Long Island Sound. Preliminary estimates by
two engineering firms placed construction costs at $500 million to $1 billion. Some of the
cost could be defrayed if the tide gate served a dual purpose, such as providing a
structure for a railroad crossing. Operational costs are anticipated to be relatively low.
This alternative is not likely to be pursued, however, because it has the potential to
change the whole ecosystem in the western Sound, resulting in unintended consequences that
are difficult to predict and may prove to be irreversible.
Advantages:
- May increase the overall circulation
in the Sound and adjacent water bodies;
- Prevents nitrogen and other pollutants
from entering the Sound from the west end;
- Causes reduction in coliform bacteria
concentrations; and
- May flush Long Island Sound and New
York Harbor with cleaner Atlantic Ocean water.
Disadvantages:
- Affects tidal heights and currents;
- May cause potential changes in flora,
fauna and fish migration patterns in the Sound;
- May alter salinity and temperature
regimes in the western Sound;
- Increases pollutant loading to New
York Harbor and the New York Bight; and
- Impedes vessel navigation in the
western Sound.
ALTERING THE BASIN MORPHOLOGY OF THE SOUND
Dredging the Mattituck Sill, East
River, and Hempstead Sill may increase water circulation in the Sound. Like tide gates,
this option has the potential to alter the ecosystem of the Sound, resulting in
consequences that are difficult to predict and may be impossible to reverse.
Advantages:
- Increases bottom water renewal from
the Atlantic Ocean;
- Can be implemented in phases, allowing
for evaluation of effects;
- May be a potential source of sand for
activities such as beach nourishment; and
- Is technologically simple.
Disadvantages:
- Presents disposal problems for any
contaminated dredged material;
- May cause changes in salinity in the
Sound and associated ecological effects;
- Is expensive;
- May have adverse effects on coastal
erosion; and
- Causes changes in characteristics of
surface sediments and benthic communities in dredged areas.
All of these alternatives are currently being subjected to
varying degrees of evaluation by LISS Management Conference participants. New York City in
particular is very interested in exploring the feasibility of an East River tide gate and
the relocation of sewage treatment plant outfalls. The development of
"systemwide" computer model, which includes Long Island Sound, New York/New
Jersey Harbor, and the New York Bight, will help assess the broader, regional impacts of
some of these alternatives.
Prepared and funded by the
Long Island Sound Study. September 1997
Sponsoring agencies: U.S.
Environmental Protection Agency, Connecticut Department of Environmental
Protection, and New York
State Department of Environmental Conservation.
Produced by New England
Interstate Water Pollution Control Commission (NEIWPCC).
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Long Island Sound Study
EPA Long
Island Sound Office
888 Washington Boulevard
Stamford, CT 06904-2152
Phone: (203) 977-1541 Fax: (203) 977-1546
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