DEAD ZONE (GULF OF MEXICO)

(Ecology) A term referring to an extensive area, recorded to be as large as 7,000 square miles (July 1995), that develops every summer at the bottom of the Gulf of Mexico. The area consists of a lifeless area devoid of oxygen that results from an ecological chain reaction precipitated by fertilizers, sewage, and runoff that flows from the Mississippi River. While many sources contribute to this phenomenon, the primary nutrient cause consists of fertilizer runoff from agriculture in the Mississippi River Basin.