The Dead Zone:

1. The Dead Zone: Hypoxia in the Gulf of Mexico

2. What is the dead zone?

3. Condition that occurs in coastal waters where: • • Little or no oxygen is present • • Little or no marine life can survive

4. The term for low oxygen is hypoxia.Hypoxia=<2 mg/l dissolved oxygen (DO)

5. The term for no oxygen is anoxia. Anoxia =0 mg/l dissolved oxygen

6. Where does hypoxia occur?

7. Hypoxia occurs all over the world in coastal waters.

8. Ireland • Scotland • Sweden • Norway • Finland • Spain • Germany • Japan • Hong Kong • Australia • New Zealand • United States • Canada • France • Italy • Greece • Turkey • Russia • Sea of Azov • Adriatic Sea • Aegean Sea • Mediterranean Sea

10. In the U.S., hypoxia occurs in coastal waters in New York, Maryland, North Carolina, Florida, Alabama, Texas and Louisiana.

11. In Louisiana, the dead zone occurs west of the Mississippi and Atchafalaya rivers

12. When does the dead zone occur?

13. In Louisiana, hypoxia occurs from late spring until late summer.

14. Why is the dead zone a problem?

15. The dead zone can affect: •Benthos •Fisheries •People

16. Benthos • Stressed or die • Decreased diversity • Degraded environment

17. Fisheries • Food base is reduced and/or lost • Habitat is reduced and/or lost • Recruitment is disrupted • Migratory patterns are disrupted • Species diversity is reduced • Mortality increases

18. People • Commercial fisheries • Recreational fisheries • Tourism • Economy

19. The dead zone decreases the ability of the Gulf to produce seafood. This affects the local economy.

20. Louisiana has one of the largest coastal dead zones in the world.

21. How large is Louisiana’s dead zone?

22. Since 1985, the dead zone has ranged in size from about 100 square miles in 1988 to over 8,500 square miles in 2002.

23. The size of the dead zone depends upon the conditions that cause it.

24. What causes hypoxia?

25. A combination of physical, chemical and biological factors create conditions for hypoxia in Louisiana.

26. Warm Temperatures Warm spring and summer temperatures heat the water surface.

27. O2 Calm seas decrease oxygen exchange at the surface.

28. Nutrients Warm fresh water and nutrients are delivered by the Mississippi River and float on the denser saltwater.

29. A stratified layer is formed with lighter, fresher, warmer water at the surface and heavier, saltier, cooler water near the bottom limiting oxygen mixing throughout the water column. Lighter Fresher Warmer Water Stratified Layer No O2 mixing Heavier Saltier Cooler Water

30. The Mississippi River drains 41% of the lower 48 United States. It carries water and sediment hundreds of miles to the Gulf of Mexico.

31. The Mississippi River also carries nutrients.

32. Excess nutrients from runoff are carried to the Gulf of Mexico.

33. Nutrients include compounds which contain: • Phosphorus • Nitrogen • Silica

34. Nutrients that are carried by the river come from a variety of sources.

35. Municipal & industrial runoff Atmosphere Fertilizers Cattle, pig and poultry farm runoff Wastewater treatment

36. Microscopic algae or phytoplankton use these nutrients to reproduce.

37. Excess nutrients enable plankton populations to explode, causing a plankton or algal bloom.

38. At the surface, plankton blooms occur when excess nutrients are present Plankton bloom

39. When plankton die, they sink and decompose

40. When plankton die, they sink to the bottom and decompose. During decomposition bacteria use up most or all of the available oxygen. Dead Plankton No O2 Decomposers

41. During decomposition, bacteria use up most or all of the oxygen causing the water column to become hypoxic or anoxic.

42. Mobile animals become stressed and leave Stationary animals become stressed and/or die

43. When little or no oxygen is present: • Mobileanimals leave. • Stationary animals become stressed or die.

44. Warm Temperatures Fresh River Water Nutrients O2 Plankton Bloom Lighter, Fresher, Warmer, Water Dead Plankton Stratified Layer No O2 Mixing Heavier, Saltier, Cooler, Water No O2 Decomposers

46. Human activities contribute to the causes of hypoxia

47. • Land use practices •Fertilizer use •Poor management practices

48. Changes in land use from Agriculture Industry Flood control Urban expansion Lead to: Loss of natural habitat

49. What can be done?

50. Change flood control practices • Use fertilizers more efficiently • Control discharges of nitrogen • Create and restore wetlands • Reduce nutrient loading • Manage the whole system