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All about “Dead Zones”

All about “Dead Zones”. Zones of Oxygen Depletion. What is Hypoxia?. Waters that have a Dissolved Oxygen (DO) concentration less than 2mg/L (<3mg/L, some systems) are defined as Hypoxia If DO= 0 mg/L, it is called Anoxia Oxygen Depletion caused by

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All about “Dead Zones”

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  1. All about “Dead Zones”

  2. Zones of Oxygen Depletion

  3. What is Hypoxia? • Waters that have a Dissolved Oxygen (DO) concentration less than 2mg/L (<3mg/L, some systems) are defined as Hypoxia • If DO= 0 mg/L, it is called Anoxia • Oxygen Depletion caused by • Excessive nutrients, intense biological productivity that depletes oxygen • Decomposition of organic matter consumes oxygen • Stratification prevents oxygen refreshment

  4. Gulf of Mexico – Dead Zone Dead Zone > 7,000 sq. miles in the Gulf of Mexico with no marine life in 1999.

  5. The Gulf of Mexico is the largest fishery in the US

  6. Hypoxia: Low dissolved oxygen (< 3 mg L-1) “And the fish are the lucky ones…”

  7. Number of fish kill events and number of fishkilled in Gulf of Mexico coastal waters, 1980 - 1989 (NOAA/ORCA 1991; USEPA 1999). Millions of fish killed Number of fish kill events

  8. Catch per unit effort in the Gulf of Mexico, 1970 - 2000

  9. Gulf of Mexico – Dead Zone

  10. The Size of the Dead Zone Correlates with Mississippi River Discharge Values

  11. Nitrogen inputs to the Gulf since 1910 1920 2000 1940 1960 1980

  12. Nitrogen loading in the Gulf triggers algal blooms, which decay and sink to the bottom. The degradation of this algal biomass results in oxygen depletion and the hypoxic / dead zones.

  13. Sources of nutrients to estuaries • Agriculture: Fertilizers • Human waste: sewage treatment plants, septic tanks, landfills • Atmosphere: Industrial emissions

  14. Annual Nitrogen Inputs to the Mississippi/ Atchafalaya River Basin 1900 1920 1940 1960 1980 2000

  15. Fertilizer use estimates for the United States, 1991 (USEPA 1999).

  16. Farm fertilizers and other nutrients flushed into Mississippi River Discharge of N into GOM stimulates algal blooms Decay of algal blooms removes bottom oxygen Simplified Model of Gulf of Mexico Dead Zone Formation Without oxygen, fish and Shrimp die or leave the GOM

  17. Pacific Northwest Dead Zone

  18. Primary ProductivityJuly-August 2005 Upwelling Season

  19. Jet Stream shifts to the North Northerly coastal winds persist 20-40 days instead of 2-5 days Persistent winds trigger ‘super-charged’ upwelling Simplified Model of Oregon Dead Zone Formation Upwelling of Nutrient-rich bottom water stimulates algal blooms Decay of algal blooms removes bottom oxygen Without oxygen, fish and crabs die or leave

  20. The End

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