The “Dead Zone” is on its way and will be growing in the Gulf of Mexico and won’t depart until autumn! No, this isn’t the latest Hollywood Horror or another terrifying installment in R.L. Stine’s “Goosebumps” series. The Dead Zone is real.
So, what is the Dead Zone? It is a huge area of the Atlantic Ocean in the northern Gulf of Mexico which cannot support most forms of marine life. The Dead Zone begins where the Mississippi River drains into the Gulf of Mexico and spreads along the coasts of Louisiana and Texas. It has been observed annually since the 1970’s and has doubled in size in the past ten years. Two summers ago, the Dead Zone covered an area the size of Massachusetts (8,500 square miles).
The problem is one of geography and seasonal weather patterns, agricultural practices, pollution, and changing uses of land in the Mississippi River watershed. To understand the problem, you need to know something about the Mississippi River watershed. The Mississippi River Basin is enormous, covering over 40 percent of the continental U.S. and all or parts of 26 states! A few of the rivers in the watershed include the Missouri, Platte, Arkansas, Ohio, and Atchafalaya.
The Dead Zone begins to form each spring when the amount of water flowing down the Mississippi River watershed increases dramatically because of melting snow and spring storms. The water carries nutrients, which contribute to the health of the river, floodplain, wetland, and ocean ecosystems – IF the amounts of nutrients aren’t too great for the ecosystems to handle. The problem is that the amounts of nutrients flowing into the Gulf of Mexico are excessive. Excessive supplies of nutrients lead to dense algae blooms. As the algae dies, it decomposes. Decomposition is a chemical process that uses up dissolved oxygen. As oxygen levels drop, there is no longer enough to support other forms of marine life. Some forms of life (such as fish) can swim to healthier parts of the ocean. Others (such as crabs and shrimp) cannot flee and are killed. The result is the Dead Zone, a huge area of the ocean where most forms of marine life can no longer be found.
Where do the excess nutrients come from? Some occur naturally in the air and soil. Most come from the nitrogen in the fertilizers that farmers use to increase their crop production. Unfortunately, the nitrogen that is not taken up by the growing plants is washed from the land and winds up in local rivers and streams. Another agricultural source of nutrients is manure. Non-agricultural sources include polluted runoff from city streets, sewage, and industrial waste. At one time, wetlands and floodplain forests in the Mississippi River basin helped filter and slow the flow of nutrients into the Gulf. The conversion of wetlands and forests for agricultural and commercial purposes has resulted in losses of these natural environmental filters.
The size of the Dead Zone peaks in the summer. Fortunately, tropical storms and hurricanes in late summer and early fall help break up the Dead Zone. The true economic impact of this annual phenomenon is not known. What is known is that it occurs in an area of the Atlantic Ocean which supports a $26 billion fisheries industry.
Suppose a 10-year plan was put into place in the Year 2005 which would reduce the size of the Dead Zone by 5% each year. If the Dead Zone covered an area of 8,500 square miles at the beginning of 2005 (before being reduced in size by 5% for the year), what would be the size of the Dead Zone at the end of 10 years (in 2014)? How many total square miles would the Dead Zone be reduced by and what percent decrease is this over the 10-year period? (Please round all of your calculations to the nearest whole number.)
Image Credit: National Public Radio, "Troubled Seas", 1/15/02, www.npr.org