The Report:
Ever since 1909, the New York City Department
of Environmental Protection has been monitoring deviations and developments
in water quality in the area surrounding New York City. Known as the New
York Harbor Survey, the analysis covers 53 stations throughout the Harbor,
and deals with the period between May and September, when the greatest
recreational use of the waters in this area overlaps the greatest impairments
to water quality.
Aquatic aerobic organisms, including fish, crabs, clams and zooplankton, require dissolved oxygen to live. By monitoring DO levels, scientists have a good indication of the ability of a particular body of water to sustain these organisms. DO tends to be more prevalent in shallower waters, and the vertical biological communities of the ocean reflect this trend. DO usually fluctuates seasonally, and is usually lowest in the late summer months. Depletion of DO can be caused by high nutrient levels, which encourages the growth of plankton and other aquatic plants. When these plants die and decompose, DO levels decrease. This phenomenon is known as eutrophication. Organic material from sewage treatment plants, sewer discharges and runoff due to rainfall also decompose, depleting DO levels. The NYCDEP measures DO levels during the daytime at a set depth of 4 feet from the water surface, as well as variable levels from the ocean bottom, and expresses the results in milligrams per liter (mg/l).
Another indicator of eutrophication is chlorophyll a, a green pigment found in plants. This pigment is used to indicate the productivity of phytoplankton, and the general productivity of the whole body of water. Productivity in water is a delicate balance; too little productivity can influence ecological food chains. At the same time, enhanced vegetative growth can lead to eutrophication and the depletion of oxygen levels. Chlorophyll a is measured at the surface of the water and is expressed as micrograms per liter of water (ug/ml).
Fecal coliform, an intestinal bacteria, indicates the presence of raw or partially treated sewage known as sludge. This bacterial is associated with many different organisms that can cause disease in humans, including bacteria, parasites and viruses, and is thus a good indicator of the ability of the water to cause diseases. Fecal coliform levels are linked to the weather, as runoff due to rainfall is the major source of sludge pollution now that sewage dumping has been banned in ocean waters. Fecal coliform is measured at the surface of the water and are expressed as number of cells per 100 milliliters of water (cells/100 ml).
The extent to which sunlight penetrates water is known as “secchi depth.” In measuring light penetration, a black and white disk known as a “secchi disk” is lowered into the water. The depth at which the disk is no longer visible is recorded, and is measured in feet. Murky water has restricted secchi depth, and could indicate decreased aquatic plant growth.
The Stats:
DO continues to improve, as it has done since
1973.
On the whole, fecal coliform has been reduced. Fecal coliform spikes
can be attributed to weather conditions; at times heavy rains cause runoff
into oceans, elevating fecal coliform levels. These spikes are usually
temporary. Summer averages for the Harbor have been in excess of New York
State standards for swimmable and fishable water ever since the 1980s.
Chlorophyll a levels have remained basically constant ever since 1986.
Fluctuations are never dramatic.
Secchi depth has also remained relatively constant.
Currently, all of these total parameters are within the state’s hightest classification recommended levels for recreational use. Isolated areas fall below these levels, but do not significantly lower the quality of New York Harbor as a whole.
The Bottom Line:
Over the last few decades, water quality in New York Harbor is has
improved considerably. This improvement is attributed to the cessation
of sewage dumping in and around New York Harbor. In fact, the ocean dumping
ban of 1992 prohibits all ocean dumping. This act has allowed the Harbor
to recover from previous dumping practices. In addition, the practice of
removing suspended organic solids from sewer runoff, known as secondary
treatment, has also lead to the improvement of water quality in New York
Harbor. As a results, fish and wildlife populations have returned, and
New York City beaches have become more healthy and enjoyable.
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