Download - The Dead Zone:
The The Dead Zone:Dead Zone:
Hypoxia in the Gulf of Hypoxia in the Gulf of MexicoMexico
What is the What is the dead zone?dead zone?
• Little or no oxygen is present
• Little or no marine life can survive
Condition that occurs in coastal waters where:
The term for low oxygen is The term for low oxygen is hypoxiahypoxia..
Hypoxia=<2 mg/l dissolved oxygen Hypoxia=<2 mg/l dissolved oxygen (DO)(DO)
The term for no oxygen is The term for no oxygen is anoxia.anoxia.
Anoxia =0 mg/l dissolved oxygenAnoxia =0 mg/l dissolved oxygen
Where does Where does hypoxia occur?hypoxia occur?
Hypoxia occurs all over the world in coastal waters.
United States Canada France Italy Greece Turkey Russia Sea of Azov Adriatic Sea Aegean Sea Mediterranean Sea
Ireland Scotland Sweden Norway Finland Spain Germany Japan Hong Kong Australia New Zealand
In the U.S., hypoxia occurs in coastal waters in New York, Maryland, North Carolina, Florida, Alabama, Texas and Louisiana.
In Louisiana, the dead zone occurs west of the Mississippi and Atchafalaya rivers
When does the When does the dead zone dead zone
occur?occur?
In Louisiana, hypoxia occurs from late spring until late summer.
Why is the Why is the dead zone dead zone a problem? a problem?
The dead zone can affect:
• Benthos• Fisheries• People
• Stressed or die• Decreased diversity• Degraded environment
Benthos
• 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
Fisheries
• Commercial fisheries
• Recreational fisheries
• Tourism
• Economy
People
The dead zone decreases the ability of the Gulf to produce seafood. This affects the local economy.
Louisiana has one of the largest coastal dead zones in the world.
How large is Louisiana’s dead zone?
Since 1985, the dead zone has ranged in size from about 100 square miles in 1988 to over 8,500 square miles in 2002.
The size of the dead zone depends upon the conditions that cause it.
What What causes causes
hypoxia?hypoxia?
A combination of physical, chemical and biological factors create conditions for hypoxia in Louisiana.
Warm spring and summer temperatures heatthe water surface.
Warm Temperatures
Calm seas decrease oxygen exchange at the surface.
O2
Nutrients
Warm fresh water and nutrients are delivered by the Mississippi River and float on the denser saltwater.
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 WarmerWater
Stratified Layer Heavier
Saltier Cooler Water
No O2 mixing
The Mississippi River drains 41% of the lower 48 United States. It carries water and sediment hundreds of miles to the Gulf of Mexico.
The Mississippi River also carries nutrients.
Excess nutrients from runoff are carried to the Gulf of Mexico.
Nutrients include compounds which contain:
• Phosphorus
• Nitrogen
• Silica
Nutrients that are carried by the river come from a variety of sources.
Fertilizers
Cattle, pig and poultry farm runoff
Atmosphere
Wastewater treatment
Municipal & industrial runoff
Microscopic algae or phytoplankton use these nutrients to reproduce.
Excess nutrients enable plankton populations to explode, causing a plankton or algal bloom.
At the surface, plankton blooms occur when excess nutrients are present
Plankton bloom
When plankton die, they sink and decompose
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
During decomposition, bacteria use up most or all of the oxygen causing the water column to become hypoxic or anoxic.
Stationary animals become stressed and/or die
Mobile animals become stressed and leave
When little or no oxygen is present:
•Mobile animals leave.
•Stationary animals become stressed or die.
Fresh River Water
Warm Temperatures
Plankton Bloom
Dead Plankton
No O2
Lighter, Fresher, Warmer, Water
Stratified Layer Heavier
, Saltier, Cooler, WaterDecomposer
s
O2
No O2 Mixing
Nutrients
Human activities contribute to the causes of hypoxia
• Land use practices• Fertilizer use• Poor management practices
AgricultureIndustryFlood controlUrban expansion
Lead to:Loss of natural habitat
Changes in land use from
What can What can be done?be done?
• Change flood control practices• Use fertilizers more efficiently• Control discharges of nitrogen • Create and restore wetlands• Reduce nutrient loading• Manage the whole system