A Big Muddy Dead Zone

Many dead zones are caused by farm fertilizers and other chemicals, and their runoff into rivers creates a large amount of plankton, which in turn depletes oxygen as it sinks down into the water. Without sufficient oxygen, marine life on and close to sediment dies.

The Mississippi is the largest river in the U.S., draining 40 percent of the land area of the country. It also accounts for almost 90 percent of the freshwater runoff into the Gulf of Mexico.

Where the Mississippi empties into the Gulf Coast is the start of the dead zone Quigg is studying – and areas where high concentrations of nitrogen, phosphorous and other substances commonly used in fertilizers are being found.

Quigg will closely examine bacteria found in the area to see if the suspected agents found in fertilizers are currently there. Spring is peak fertilizing time for many farmers and ranchers all along the Mississippi River, meaning the suspected runoff of these chemicals into the Gulf Coast area will be reaching a climax in the weeks ahead.

“We will look at the nutrients in the water in the dead zone area, look at the water color and examine the bacterial communities,” she says.

“We want to determine what specific biological activities are going on there – and their interactions with the chemical and physical environment. Whatever is happening is causing a large amount of marine life to die.”

Studies by the United Nations Environment Program show that the number of dead zones in the world’s oceans has increased steadily in the past 25 years, and there are now about 150 dead zones worldwide.

Because it has created a quick-acting dead zone, the Mississippi River delta area has become one of the most famous dead zones in the world, but other recent ones have occurred in South American, Japan, China and Australia, the United Nations report says.

Dead zones range in size from just a few square miles to more than 45,000 square miles, and the loss of fish and other marine life can be immense.

“Dead zones seem to have one thing in common, and it’s that they’re getting bigger,” says Quigg. “In our study, we hope to find some definitive answers on what is causing the dead zone in the Mississippi River Delta area.”