hypoxia deadzone

Bottom-water dissolved oxygen concentrations for July 21-28, 2007 (A. Sapp, LUMCON).

Hypoxia Barchart

Forecasts from LimnoTech model for improvements in dissolved oxygen concentrations due to nitrogen load reductions from the Mississippi River Basin.

Shedding light on the Gulf's "Dead Zone"

The Gulf of Mexico is critically important to America’s economic and ecological well-being, yet human activities in the watershed have taken their toll on the system. The Mississippi and Atchafalaya Rivers bring large quantities of fresh water and nutrients into the Gulf, sustaining a rich ecosystem. However, these nutrients have become excessive and for decades the northern Gulf has been plagued by dissolved oxygen levels so low they cannot sustain aquatic life, a condition called hypoxia. Nutrient loads originating primarily from agricultural activity in the watershed stimulate the growth of phytoplankton, which settle into the bottom waters and decompose, depleting oxygen. Every summer, a “Dead Zone” forms off the coast of Louisiana. Continuing to expand, it is sometimes larger than the state of Massachusetts.

The journal Estuaries and Coasts recently published a review paper on this issue, co-authored by LimnoTech senior scientist Victor Bierman. A key conclusion (based on available model results) is that large-scale hypoxia probably did not begin until the mid- 1970s, and that the 30% nitrogen load reduction that is called for by the 2001 Federal Action Plan may not be sufficient. Rather, predictions from a suite of different forecasting tools, including a model developed by LimnoTech, indicate that a 40 to 45% reduction in nitrogen load may be necessary to achieve the desired reduction in hypoxia. Accomplishing this level of reduction will be a significant challenge in the years ahead.

The LimnoTech model greatly advanced our understanding of hypoxic conditions in the northern Gulf of Mexico and the prediction of probable consequences of various management actions. Our scientists will continue to contribute their expertise to this national environmental problem in the years ahead.

The size of the hypoxic zone in the Gulf of Mexico for 2008 was over 20,270 square kilometers (8,000 square miles), reported  Dr. Nancy Rabalais and a team of scientists from Louisiana Universities Marine Consortium (LUMCON)(download pdf).  This was the second largest area of hypoxia since mapping began in 1985, rivaling the area measured in 2001.


Complete publication: "Forecasting Gulf’s Hypoxia: The Next 50 Years?" by Justić, Bierman et al. (click here to download pdf)

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