Much of Louisiana was built by the sediments brought down over millennia by the great Mississippi River, and it continues today to generate wealth in this country and state as one of the world’s great highways of trade.
But being at the mouth of the Mississippi is not an unalloyed benefit.
Nancy Rabalais has been tracking for decades the occurrence of one of the great river’s less salutary effects, an annual “dead zone” in the Gulf of Mexico. This year’s is the largest ever.
The low-oxygen zone covers 8,776 square miles, about the size of New Jersey, the National Oceanic and Atmospheric Administration said Wednesday. The area is more than 3 percent larger than the 2002 dead zone, the previous record.
Rabalais, of LSU and the Louisiana Universities Marine Consortium in Cocodrie, told The Associated Press that winds from the west and southwest slightly compressed the area of this year’s zone, so it might have been larger.
The zone is caused by nitrogen and phosphorus in the Mississippi River. The nutrients feed plankton blooms that die and sink to the bottom, where their decay uses oxygen.
“This large dead zone size shows that nutrient pollution, primarily from agriculture and developed land runoff in the Mississippi River watershed is continuing to affect the nation's coastal resources and habitats in the Gulf," NOAA said in a news release.
A NOAA-funded study led by Duke University in North Carolina found that the Gulf dead zone hurts one of Louisiana’s big exports, and favorite delicacies, shrimp. Fewer large shrimp were found in that survey.
This “dead zone” effect has been known for a long time. Doing something about it is difficult.
A national action plan calls for reducing runoff into the river so that the dead zone shrinks by two-thirds, to 1,950 square miles (5,000 square kilometers) by 2035.
Far easier said than done, as the river drains much of the United States, including the immensely valuable farmlands of the Midwest. While the river brings those products to the world markets, it also brings fertilizers and other runoff that contribute to the dead zone.
Inevitably, with private economic interests and many state and local governments along the midsection of the country, the national action plan has to be truly national — the United States government must take on more of a leadership role in getting everybody on board with specific ways to reduce nutrient runoff.
Meeting the national goal would require cutting the amount of nitrogen flowing into the river by 59 percent, according to a study published online Monday in Proceedings of the National Academy of Sciences.
"While there are undoubtedly significant lag times between action on the land and changes in loads, river nitrate concentrations have not declined since the 1980s," Donald Scavia, of the University of Michigan, and his co-authors wrote.
That’s not helping the Gulf.