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August 26, 2011

Algal Bloom

A huge algal bloom, indicated by the green color in the ocean water, was observed on August 17, 2011.  The bloom covered much of the New York Bight area which extends from Montauk, NY (the tip of Long Island) to Cape May, NJ.  This spells potential harm to marine life, especially bottom living animals such as lobsters, clams, crabs, and some fish.  As the algae dies and decomposes it will decrease the amount of oxygen in the water on which marine life depend.

More science is needed to monitor the impacts of the bloom.

Divers and fisherman that know these waters should look for tell-tale signs of low dissolved oxygen (DO).  Fishermen should be looking for fish floating on the surface or in the open and lethargic.  Also look for fish that are located higher on the wrecks and/or breathing with difficulty.  If divers know how to use dissolved oxygen kits, they should take samples. 

So, what is this?

Very small, usually microscopic, types of floating algae are known as "plankton algae."  When present in large numbers, plankton algae give the water a brown, yellow, red, or green color.  Although they are not flowering plants, when enough algae are present to color the water, it is called and "algal bloom."  When there is an algal bloom, each milliliter of water contains thousands, or perhaps millions of alga cells. 

Most organisms, including algae, use oxygen for respiration.  When there are too many algae competing for a place in the sunlight, many of the algae die and decay.  This creates a demand for oxygen.  When the weather brings a series of warm, calm and cloudy days, the algae cannot produce enough oxygen to meet the needs of all the aquatic organisms. 

Some fish require high levels of (DO).  When the amount of DO in the water is not sufficient to meet their needs, the fish die.  Too many algae may cause a "fish kill" (the death of many fish at one time). 

What causes an algal bloom?

Most fertilizers, used by farmers and homeowners, contain nitrates (NO3).  All nitrates are soluble in water.  When it rains, the nitrates from fields and lawns are carried into nearby streams and lakes.  Another major source of nitrates is sewage produced by humans and other animals.  One cow produces waste equal to the sewage produced by 4.5 humans.  Nitrogen is also released by the decomposition of organic matter.

The nitrates in a body of water are nutrients for algae and aquatic plants.  This increased growth of algae and build-up of dead plant material causes an increase in the biochemical oxygen demand (BOD) and lowers the DO level of the water.  The Environmental Protection Agency (EPA) has identified nitrogen as the main factor causing low oxygen levels in the western part of Long Island Sound.

Unpolluted waters generally have a very low nitrate-nitrogen level (below 1ppm).  Fast-flowing water will prevent the growth of floating aquatic plants and plankton algae even when nitrate levels are high.  In the lower reaches where the water is warmer and slower moving, the nitrate causes abundant growth of algae, an "algal bloom."  The algae die and settle to the bottom and their decay causes the DO level to fall.

Additionally, secondary treatment at some sewage treatment plants does not produce effluent that meets the EPA standard for nitrates and phosphates.  Without further treatment, the effluent will pollute streams and cause algal blooms. 

I will continue to keep you updated as I learn more about the current algal bloom off the coast of New Jersey and Long Island. 

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