Flood Water Plus Fertilizer Runoff Creates a Dead Zone the Size of New Jersey

20 May 2011

gulf of mexico, dead zone, mississippi river, mississippi river flood, great flood of 2011, dead zone
Natural processes used to occasionally create a "dead zone" of oxygen-poor water grows in the waters of the Gulf of Mexico. It would happen when nutrients from upstream got washed out to sea, feeding phytoplankton in the area. As that phytoplankton population exploded, and then decomposed, bacteria would absorb the water’s oxygen, making it deadly to animals, from crustaceans to fish.

But these days farming fertilizers provide a regular source of nutrients to the phytoplankton, and the dead zone is a regular thing. NASA’s Earth Observatory explains:

Once infrequent, the Gulf of Mexico dead zone is now an annual event, triggered by phosphorus and nitrogen in fertilizers used on farms throughout the central United States and as far away as Saskatchewan, Canada. In the fall, strong winds from seasonal storms stir the water, mixing the oxygen-poor deep water with oxygen-rich surface water, bringing a reprieve until the next spring.

It stands to reason, then, that the record flood swell right now making its way down the Mississippi River is going to pull a lot more of that nitrogen-rich fertilizer runoff into the Gulf and make that dead zone even bigger than normal years. Jenny Marder reports for PBS that this summer’s dead zone is already the size of New Jersey, and growing. Marder quotes a marine scientist who warns that this will be the "largest ever amount of hypoxia," the phenomenon that causes the dead zone. It’s also going to make life even tougher for already-suffering fishermen in the region:

Flooding could cause further injury to fisheries in the northern Gulf of Mexico, already reeling from last year’s oil spill, Rabalais said. Dead zones alter the habitat for crab, shrimp, fish and lobster, often forcing them to shallow areas. This includes catchable seafood, like shrimp and snapper, which are vital to the area’s fisheries.

After the Deepwater Horizon and the oil plume that still to this day is beaching tar balls, the last thing Gulf fishermen need is another "unnatural disaster" to deal with.

Photo: NASA Earth Observatory