Tuesday, 13 January 2009: 11:45 AM
Dead Zones Grow With More Precipitation, Animals and Fuel Demand
Room 230 (Phoenix Convention Center)
Dead, or hypoxic, zones in coastal waters that are devoid of most marine life, are growing in size and number around the world, threatening valuable fisheries. Weather, climate and the atmosphere are major factors in this trend. Precipitation washes the increasing amounts of nutrients (N and P) applied to land from fertilizers and animal waste into streams and eventually out into the coastal zone. Demand for biofuels has driven more land into agricultural production along with additional use of fertilizers. These excess nutrients stimulate vast algal blooms along the coast which eventually sink to bottom waters, decompose and, in the process, deplete life-giving oxygen. High freshwater inputs from major rivers also cause increased stratification of estuarine and coastal water into lighter surface layer and heavier, salty bottom layer; this restricts mixing, making bottom waters more susceptible to becoming hypoxic. Precipitation can also transport large amounts of airborne reactive nitrogen injected into the atmosphere from combustion of fossil fuels and ammonium volatilization. Ironically, the atmosphere is further connected to this trend as the primary source of N for the production of nitrogen fertilizer produced by the Haber-Bosch process in increasing amounts since its invention in the early 20th century. Climate change brings additional threats since warmer waters hold less oxygen and any increases in the frequency of storms could lead to even greater runoff of nutrients. In 2008, the northern Gulf of Mexico dead zone, the largest in N. America, was predicted to reach record size due to flooding in the MS River basin but mixing, due to the passage of a hurricane, reduced the aerial extent to second on record.