Download The Dead Zone - stjoescience2012

The Gulf of Mexico’s Dead Zone
Where do most shrimp served in
restaurants around the Gulf of Mexico
come from?
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Video
http://www.pbs.org/newshour/bb/weather/jan-june11/floods_05-18.html
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What do YOU think might be the reason
why shrimp have disappeared from local
waters?
A. Overfishing has depleted shrimp populations.
B. Pollution has killed off shrimp populations.
C. Rising water temperatures caused by climate
change have made the habitat inhospitable to
shrimp.
D. Hurricane Katrina and the BP Oil Spill
destroyed all the shrimp and their habitat.
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“Dead Zone” refers to a lack of oxygen in
a region of water
• Normal oxygen levels: ~ 4.8 mg/L
• Hypoxia: < 2-3 mg/L
• Anoxia: 0 mg/L
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The four working hypotheses for the Dead
Zone are:
•
•
•
•
•
Hurricane Katrina
BP Oil Spill
Pollution
Climate change
Overfishing
Can you think of other hypotheses?
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What does this graph tell you about the
average shrimp catch over time?
The graph shows annual changes of CPUE for brown shrimp in areas of the Gulf of
Mexico. The colored bars are “decadal means.” They show the average CPUE for
a span of ten years (CPUE = catch per unit effort). Data: James Nance, National
Marine Fisheries Service.
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Which hypothesis does this graph NOT
support?
A. Hurricane
Katrina/BP Spill
B. Pollution
C. Climate Change
D. Overfishing
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The four working hypotheses for the Dead Zone:
•
•
•
•
Katrina/Oil Spill
Pollution
Climate Change
Overfishing
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Gulf Coast at the mouth of the Mississippi River
Source: NASA Earth Observatory
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What are the tan/brown regions in the
picture in the Gulf?
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What are the green regions in the picture
in the Gulf?
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What are the black regions in the picture in
the Gulf?
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What requires oxygen in a aquatic
ecosystem?
What can be an effect of a lack of
oxygen?
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Cellular Respiration
Inputs: Oxygen, Glucose
Outputs: Carbon Dioxide, ATP, Water
All organisms require cellular respiration
to survive
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What is a source of oxygen in an
ecosystem?
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Photosynthesis
Inputs: Carbon Dioxide, Sunlight, Water
Outputs: Glucose, Oxygen
Major source of food for ecosystem food
webs/chains
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What could be “stealing” all of the
oxygen from the dead zone area?
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Identify producers, consumers, herbivores, omnivores
What is the ultimate source of energy for the ecosystem?
Why is it better to use a food web rather than a food chain?
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Hypoxia Causes
Source: http://www.eco-check.org/forecast/chesapeake/methods/
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What are the tan/brown regions in the
picture in the Gulf?
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What are the green regions in the picture
in the Gulf?
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What are the black regions in the picture in
the Gulf?
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What affect does hypoxia have on the
production in the Gulf of Mexico?
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What affect does hypoxia have on the rate
of respiration in the Gulf of Mexico?
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Do the dead zone areas vary throughout
the year (are they always really dead)? Can
the amount of nitrogen affect this?
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Conclusions so far
Hypoxia/ Lack of Oxygen is
caused when the decomposition
of large
amounts of producers
(phytoplankton/ algae) occur
This decomposition/hypoxia
causes the death of
zooplankton/smaller fish (basis
of food chain/web); other
organisms either die or avoid
area
Large amounts of
nitrogen/phosphorus, warmer
water, no wind cause
algae/phytoplankton bloom,
eventually resulting in dead
zone
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What causes large amounts of nitrogen
and phosphorus?
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Interior Watersheds of the Mississippi
River Basin
Largest river basin in North America.
Third largest basin in the world.
Includes 70 million people, 30 states.
One of the most productive farming
regions in the world:
~60% of the basin is cropland
( corn, soybeans, wheat)
~20% woodland,
~20% barren land,
~2% wetland, and
~ 0.6% urban land
(Goolsby and Battaglin, 2000 )
Source: USGS Fact Sheet 016-00
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What does this figure tell you about the runoff to
the Mississippi River basin over time?
Source: USGS Fact Sheet 135–00
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What does this figure tell you about the runoff to
the Mississippi River basin over time?
Source: USGS Fact Sheet 135–00
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What do these figures tell you about the runoff
to the Mississippi River basin over time?
A.
B.
C.
D.
E.
Annual nitrate concentrations have increased over time.
Stream flow has remained constant over time.
The biggest source of nitrates is the area farthest from the Gulf of Mexico.
Only A and C.
A, B, and C are true.
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http://serc.carleton.edu/images/microbelife/microbservatories/northinlet/Nitrogen_Cycle
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What is the most likely source of nitrogen
in runoff?
A. Fossil fuel
emissions.
B. Organic matter.
C. Leaching of
nitrates from
nitrification.
D. Fertilizer runoff.
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CQ#6: When the freshwater river flows into
the saltwater Gulf, what do you predict will
happen?
A. The freshwater and the saltwater will mix, lowering
the overall salinity of the Gulf.
B. The warmer freshwater will sink to the bottom of the
Gulf, and the colder saltwater will float above.
C. The less dense freshwater will float on top of the
more dense saltwater.
D. The amount of freshwater entering the Gulf is so
small compared to the total volume of the Gulf that
there will be no noticeable effect of the freshwater
input.
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What Happens Next?
• Excess nitrogen and more sunlight in surface waters leads to algae blooms.
• The algae bloom provides food for zooplankton.
• Zooplankton
wastes and dead
algae sink to the
bottom of the Gulf
and decomposition
lowers oxygen
levels.
• Continuing
decomposition by
bacteria lowers
oxygen levels
even more.
Source: http://www.epa.gov/msbasin/taskforce/hypoxia.htm
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Does the evidence you’ve seen so far
mean that climate change and overfishing
are NOT to blame for the decline of the
shrimp fishery?
A. Yes
B. No
The four hypotheses for the Dead Zone:
• Katrina/Oil Spill
• Pollution (Nitrogen runoff from farms)
• Climate Change
• Overfishing
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Suppose you are on a government panel
studying the Dead Zone problem.
What recommendations would you make
for solving the problem of the Dead Zone?
Who should be responsible for fixing the
problem, and what actions should they
take?
Cooperative work by universities, state
and federal agencies have come up with
the following recommendations:
• Make a watershed-wide plan.
• Restore millions of riverside wetland and forest
acres at a cost of billions of dollars.
• Establish a nitrogen credit system with
incentives for the agricultural industry to reduce
nitrogen-based fertilizers.
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