Every summer the Gulf of Mexico experiences an enormous dead zone. This dead zone occurs at the mouth of the Mississippi River and is the result of excess nutrients released into the Gulf. What happens is that these excessive nutrients, along with the summer heat, cause algae blooms to run rampant. The growth of this algae blocks sunlight from penetrating to lower layers of water and causes a hypoxic environment to occur.
A hypoxic environment is one where there are low dissolved oxygen concentrations. This is caused by the decomposition of the algae, during which bacteria use up a large portion of the dissolved oxygen. Without sufficient dissolved oxygen concentrations, the marine life has to leave the area, or ends up dying. As you can imagine, this dead zone along the Louisiana coast has huge implications for fisheries. The shrimp and fish can often move to waters with higher oxygen levels, but other animals, such as mussels and crabs, with less mobility are unable to escape. With many larger animals able to migrate, but with much of their food sources being unable to, this leads to a large disruption in the distribution and supply of the food chain.
This past summer, the dead zone covered 5,052 square miles, or roughly the size of the state of Connecticut. Louisiana, which is known for its seafood market, takes a large hit as the dead zone covers nearly its entire coastline. One of the saddest parts of this issue is that the problem is caused, not locally, but by people up to 1,000 miles away. The fertilizers used on farms and waste-water released from sewage treatment plants in Indiana, Illinois, Iowa, and many other areas within the Mississippi River Basin are the largest contributors to this problem.
Because the problem stems from numerous sources, spread out across a large area, it is difficult to control and mitigate. Farms along the Mississippi River Basin rely on heavy fertilizer use to grow crops for consumption across the U.S., and without control measures in place, these nutrients easily run-off into the Mississippi River. While there are some simple ways to help mitigate this problem, until there are set limits, or controls, on nutrient run-off levels there is no incentive for the farmers of the Midwest, who are far removed from the problem, to change their current behaviors.