![]() ![]() states, collecting the sediment, fresh water and nutrients from the one-million-square-mile drainage basin, bringing them south to Louisiana and the Gulf of Mexico. The Mississippi River and its tributaries meander more than 2,000 miles through parts of 32 U.S. ![]() For fish and marine mammals, the Dead Zone can cause them to move away into deep waters. Non-swimming and weak-swimming animals can die if they are trapped in the low-oxygen area. Results released from the annual cruise, led by Louisiana State University scientists found the Dead Zone was nearly 7,000 square miles – the 8 th largest ever measured. This year, the river was in flood stage for more than 240 days at Red River Landing, an unprecedented length of time. The size of the Dead Zone generally depends on the quantity of fresh water and nutrients entering the Gulf of Mexico from the Mississippi and Atchafalaya Rivers. At other times during the year, winds, weather fronts and storms in the area mix the water, replenishing the oxygen used by the bacteria in the deeper water. ![]() This occurs when there are fewer storms and strong winds to mix the warm, oxygenated surface waters and the cooler, deeper waters. This lack of oxygen creates the Dead Zone in bottom waters on the Texas-Louisiana shelf throughout warm summer months. As dead plant material falls from the surface through the water column deeper into the Gulf, bacteria consume it using oxygen. The Dead Zone develops, somewhat ironically, as a result of the nutrients that fuel the high productivity in the Gulf’s surface waters. Mobile fish and marine mammals are able to swim away from the low oxygen area, but weaker swimming organisms can be trapped and die, leaving behind a barren area that would typically be teeming with life. While it seems contradictory, nutrients brought in from the river that fuel the region’s plant, wildlife and fisheries productivity are the same nutrients that contribute to the formation of a low-oxygen area along parts of the Gulf’s seafloor. Every summer, a low-oxygen area, often referred to as a Dead Zone, develops off of the Texas-Louisiana shelf when nutrient-laden fresh water from the Mississippi and Atchafalaya Rivers flows into the Gulf of Mexico. ![]()
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