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Historical Trends in Nitrogen to Phosphorus Ratios in the Gulf of Mexico as Related to the "Dead Zone"
Historical Trends in Nitrogen to Phosphorus Ratios in the Gulf of Mexico as Related to the "Dead Zone"
Abstract
Coastal hypoxia is a widespread environmental problem in the United States. Forty out of one hundred thirty eight estuaries in the U.S. exhibit moderate to severe hypoxia. In addition to faunal mortalities, persistent low oxygen conditions can also reduce critical habitat areas. Much publicity, research and policy attention has been given to the extensive hypoxic zone in the Gulf of Mexico commonly referred to as the “Dead Zone.” Bottom water oxygen concentrations of less than 2 mg/L form in large areas off the Louisiana coast annually during the spring and summer. The size of this hypoxic area averaged 8,300 km2 from 1985 to 1992 and increased to an average of 16,000 km2 from 1993-2001, with a maximum size of over 20,000 km2 in 2003.
One of the keys to understanding the Dead Zone is understanding the relative importance of nitrogen vs. phosphorus ratios. By examining historical N:P ratios, in light of the Redfield ratio, we can better understand whether this system in N limited or P limited, and how this nutrient condition has changed over time.
Objectives
Time Frame
2006.
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