Sea dead zones – 03/25/2004

  • September 30, 2013 at 6:09 pm #412

    By Alex Kirby
    BBC News Online environment correspondent in Jeju, Korea

    Oxygen depletion: Set to have a big impact in the 21st century
    Sea areas starved of oxygen will soon damage fish stocks even more
    than unsustainable catches, the United Nations believes.
    The UN Environment Programme says excessive nutrients, mainly
    nitrogen from human activities, are causing these “dead zones” by
    stimulating huge growths of algae.

    Since the 1960s the number of oxygen-starved areas has doubled every
    decade, as human nitrogen production has outstripped natural sources.

    Unep made its remarks as it launched its Global Environment Outlook
    Year Book 2003.

    Human disturbance

    About 75% of the world’s fish stocks are already being overexploited,
    but Unep says the dead zones, which now number nearly 150 worldwide,
    will probably prove a greater menace.

    Unless urgent action is taken to tackle the sources of the problem,
    it is likely to escalate rapidly

    Dr Klaus Toepfer
    Unep executive director
    It quotes research by a team of scientists at the Virginia Institute
    of Marine Science in the US.

    They concluded: “The history and pattern of human disturbance in
    terrestrial, aquatic, coastal and oceanic ecosystems have brought us
    to a point at which oxygen depletion is likely to become the keystone
    impact for the 21st Century, replacing the 20th Century keystone of

    Ironically, Unep says, nitrogen is desperately needed in parts of the
    world, including much of Africa, where the lack of it is reducing
    farmers’ yields.

    Washed away

    The amount of nitrogen used as fertiliser globally is 120 million
    tonnes a year, more than the 90 million tonnes produced naturally.

    Yet only 20 million tonnes of that is retained in the food we eat,
    with the rest washed away into rivers and out to sea.

    The burning of fossil fuels in vehicles and power plants, and of
    forests and grasslands, and the draining of wetlands all contribute
    more nitrogen to the cycle.

    This leads to the explosive blooms of algae, tiny marine plants,
    which sink to the seabed and decompose, using up all the oxygen, and
    suffocating other marine life.

    Unep’s executive director, Dr Klaus Toepfer, said: “Humankind is
    engaged in a gigantic global experiment as a result of the
    inefficient and often excessive use of fertilisers, the discharge of
    untreated sewage, and the ever-rising emissions from vehicles and

    “Hundreds of millions of people depend on the marine environment for
    food, for their livelihoods and for their cultural fulfilment. Unless
    urgent action is taken to tackle the sources of the problem, it is
    likely to escalate rapidly.”

    Remedies available

    Some of the dead zones are less than a square km in size, while
    others are up to 70,000 sq km. Examples include Chesapeake Bay in the
    US, the Baltic and Black Seas and parts of the Adriatic.

    One of the best-known is in the Gulf of Mexico, affected by nutrients
    washed down the Mississippi river.

    Other zones have appeared off South America, Japan, China, Australia
    and New Zealand.

    Not all are permanent: some appear annually or only intermittently.

    Unep says reducing nitrogen discharges can restore the seas to
    health: an agreement by states along the River Rhine has cut the
    amount of nitrogen entering the North Sea by 37%.

    Other remedies include wasting less fertiliser, cleaning vehicle
    exhausts, and using forests to soak up excess nitrogen.

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