The Other Gulf Stain

By ANDREW C. REVKIN, The New York Times
August 2, 2010

To the west of the oil slicks and fleets of vessels working to seal the BP well, another less invisible stain, mainly the result of vast amounts of nitrogen and other nutrients washing down the Mississippi River from agricultural lands upstream, has spread beneath the waters of the Gulf of Mexico. It is the annual blossoming of a zone of low dissolved oxygen levels, anathema to fish, shrimp and other marine life, known colloquially as the “dead zone.”

This year’s hypoxic zone, nearly the size of the state of Massachusetts, is right in the range predicted earlier in the year by the Louisiana Universities Marine Consortium, which does a yearly survey of oxygen levels. Here’s a map of the findings:

When I canvassed marine biologists and other experts late last week to get their forecasts of the long-term environmental impacts of the Gulf of Mexico oil gusher, one scientist, Nancy Rabalais, sent an apologetic note from the cruise charting oxygen levels, saying she had no time to weigh in because the expedition was wrapping up its survey. Late Monday night, she sent the release below, summarizing the findings:


The area of hypoxia, or low oxygen, in the northern Gulf of Mexico west of the Mississippi River delta covered 20,000 square kilometers (7,722 square miles) of the bottom and extended far into Texas waters. The relative size is almost that of Massachusetts. The critical value that defines hypoxia is 2 mg/L, or ppm, because trawlers cannot catch fish or shrimp on the bottom when oxygen falls lower.

This summer’s hypoxic zone (“dead zone”) is one of the largest measured since the team of researchers from Louisiana Universities Marine Consortium and Louisiana State University began routine mapping in 1985. Dr. Nancy Rabalais, executive director of LUMCON and chief scientist aboard the research vessel Pelican, was unsure what would be found because of recent weather, but an earlier cruise by a NOAA fisheries team found hypoxia off the Galveston, Texas area. She commented “This is the largest such area off the upper Texas coast that we have found since we began this work in 1985.” She commented that “The total area probably would have been the largest if we had had enough time to completely map the western part.”

LSU’s Dr. R. Eugene Turner had predicted that this year’s zone would be 19,141 to 21,941 square kilometers, (average 20,140 square kilometers or 7,776 square miles), based on the amount of nitrate-nitrogen loaded into the Gulf in May. “The size of the hypoxic zone and nitrogen loading from the river is an unambiguous relationship,” said Turner. “We need to act on that information.”

The size of the summer’s hypoxic zone is important as a benchmark against which progress in nutrient reductions in the Mississippi River system can be measured. The Mississippi River/Gulf of Mexico Nutrient Management Task Force supports the goal of reducing the size of the hypoxic zone to less than 5,000 square kilometers, or 1,900 square miles, which will require substantial reductions in nitrogen and phosphorus reaching the Gulf. Including this summer’s area estimate, the 5-year average of 19,668 square kilometers (7,594 square miles) is far short of where water quality managers want to be by 2015.

Read the rest…

Here’s some more background from the 

United States Geological Survey andGrist