What is the Dead Zone?
Gulf Restoration Network
The Dead Zone is an area in the Gulf of Mexico where oxygen levels in the water are too low to support life. The Dead Zone forms seasonally off the coast of Louisiana and Texas. Those fish, crabs, and shrimp that can swim away from the Dead Zone do so, while others simply die. Since 1993, the size of the Dead Zone has averaged 16,000 square kilometers, though its size varies every year.1 The lack of oxygen in the Dead Zone poses a serious threat to species diversity in the Gulf and to the $2.8 billion commercial and recreational fishing industry.2 For example, the amount of brown shrimp caught declines in years when the Dead Zone is its largest, and shrimpers must look elsewhere for their catch.3
The Creation of the Dead Zone
When the Mississippi River reaches the Gulf of Mexico, it is loaded with nitrogen and phosphorus pollution. The polluted water acts as a fertilizer of algae, resulting in large algal blooms. When the algae die, they sink to the saltier water below and decompose, depleting already low oxygen in the deeper water. Because the salty bottom waters do not mix well with the lighter, fresh water from the Mississippi River, oxygen in the water is not replenished, resulting in a large dead zone in bottom waters. |