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    Post: Recent Report on the Dead Zone

    Posted by Mike B. on 1/31/08

    Most of Gulf Dead Zone Nutrients Come from Just Nine States

    RESTON, Virginia, January 30, 2008 (ENS) - Nine states in
    the Mississippi River Basin contribute the majority of
    nutrients to the northern Gulf of Mexico, threatening the
    economic and ecological health of one of the nation's
    largest and most productive fisheries, according to a
    federal government report released Wednesday.

    The states of Illinois, Iowa, Indiana, Missouri, Arkansas,
    Kentucky, Tennessee, Ohio and Mississippi make up only one-
    third of the 31-state Mississippi River drainage area, but
    contribute more than 75 percent of nitrogen and phosphorus
    to the Gulf, U.S. Geological Survey, USGS, researchers

    Excess amounts of these nutrients have resulted in a zone
    of low dissolved oxygen or hypoxia, caused by the growth of
    large amounts of algae. This can stress and cause death in
    bottom-dwelling organisms in the Gulf, so it is commonly
    called the dead zone.

    The study found that agricultural nonpoint sources
    contribute more than 70 percent of the nitrogen and
    phosphorus delivered to the Gulf. By comparison, only about
    nine to 12 percent originates from urban sources.

    Corn and soybean cultivation is the largest contributor of
    nitrogen to the Gulf. Animal manure on pasture and
    rangelands and crop cultivation are the largest
    contributors of phosphorus.

    These are among the new findings in the
    report, "Differences in Phosphorus and Nitrogen Delivery to
    the Gulf of Mexico from the Mississippi River Basin," by
    the U.S. Geological Survey, USGS, published in the
    journal "Environmental Science and Technology. "

    "This study is important because it reveals new details
    about sources of phosphorus," said Richard Alexander, USGS
    scientist and lead investigator. "The report shows that
    animal manure on pasture and range lands contribute nearly
    as much phosphorus as cultivated crops, 37 versus 43

    The study suggests that phosphorus associated with the
    wastes of unconfined animals is a much larger source of
    phosphorus in the Mississippi River Basin than previously
    recognized. Current animal manure management emphasizes
    controlling nutrients primarily from confined animal

    Delivery of nutrients to the Gulf was found to be highest
    from watersheds in the central and eastern portions of the
    Mississippi River Basin that are drained by large, fast
    flowing rivers with very little natural removal.

    Runoff entering Fall Creek in Indianapolis, Indiana (Photo
    by Charles Crawford courtesy USGS)
    Alexander concludes that nutrient reductions in the Gulf
    may be most efficiently achieved by managing nutrients in
    watersheds drained by large rivers.

    Reservoirs, particularly common in the Tennessee Valley and
    along the Missouri River, are effective at removing
    phosphorus from watersheds in the Mississippi Basin, but
    Alexander and his team found that this creates water
    quality issues in the reservoirs themselves.

    The joint federal-state Gulf of Mexico Hypoxia Task Force
    is evaluating recommendations by the U.S. Environmental
    Protection Agency's Science Advisory Board to set reduction
    targets of at least 45 percent for both nitrogen and

    The targets would be set in an effort to shrink the size of
    the dead zone in half to 5,000 square kilometers by 2015.

    USGS Associate Director for Water Dr. Robert Hirsch
    says "on-the-ground" water monitoring is essential to
    provide credible, comparable data to verify computer
    modeling predictions across large regions, such as the
    Mississippi River Basin.

    Yet surface water quality monitoring stations are
    disappearing. Only 35 stations exist today, down from about
    425 stations in the early 1990s, Hirsch said.

    Hirsch says this study shows that nutrient issues are
    complex and management of animal and crop production,
    control of nutrient sources in close proximity to large
    rivers, and consideration of reservoir effects on
    phosphorus all are necessary to reduce the nutrient burden
    flowing in the Mississippi River Basin.

    Copyright Environment News Service (ENS) 2008. All rights

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