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