Lab 16
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Lab 16
Dead Zones
Description of the Lab
Students will investigate the effect of the addition of liquid plant fertilizer on water
quality as a simple model of eutrophication. Broader implications of eutrophication will
Laboratory Materials and Equipment for Student Use
Materials and Equipment
Per
Student
Per Pair of
Students
Per Lab
Group
Per
Room
1 L clear plastic soda bottles (clean
and dry)
4
mL or 10 mL)
Pipette pumps of appropriate size
Graduated cylinders (500 mL or 1L)
1
Grease pencils or labeling tape and
markers
1
Access to light source
1
Fresh or Live materials
Seawater or pond water (must contain
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live phytoplankton)
Reagents
Liquid plant fertilizer, mixed
according to manufacturer’s
Outline of Investigation
Exercise 1 – The Effect of Fertilizer on Water Quality
Materials needed:
• 4 L of seawater per group (or pond water*)
• 1-liter clear soda bottles (4 per group)
• Liquid plant fertilizer, mixed according to manufacturer’s directions
Note: To finish exercise 1, students will need time in subsequent lab periods to test
water quality. The number of follow-ups and the appropriate spacing will depend on the
initial plankton concentrations in your water samples. If you do not have access to fresh
seawater or pond water, cultures of phytoplankton ordered from a biological supply
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Exercise 2 – Size of the Gulf Dead Zone Over Time
Materials needed:
• Data provided in lab manual
Answers to Questions for Lab 17
Exercise 1 – The Effect of Fertilizer on Water Quality
a. What differences did you observe between your treatment groups?
b. Did the addition of the fertilizer result in hypoxia in all three experimental groups? Why
or why not?
c. What processes important to the discussion of real hypoxic zones are NOT modeled in
this experiment?
Answers will vary e.g., Eutrophication is modeled in a simple way but water column
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Exercise 2 – Size of the Gulf Dead Zone over Time
a. What is the trend in the size of the dead zone in the Gulf of Mexico over time?
There is a very general trend towards increasing from the 1980s to the
b. Why is the size of the dead zone so variable?
Answers will vary, e.g., the way the data are collected represents a two dimensional
c. 1993 was the year of a major flood even on the Mississippi River. What effect did that
event had on the size of the dead zone? Explain.
d. Data were collected in midsummer over a 5 day period by a team of scientists on a
research vessel. Research cruises in 2003, 2005, 2006, 2008 and 2010 were preceded by
hurricanes. What effect do you think that had on the results?
e. What river outflow pattern would explain the data from 1988 and 2000?
Low river discharge, e.g., in drought years
f. Could the measurements of the area of the dead zone (km2) be misleading if you were
interested in changes in overall size?
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Answers to Questions for Lab 16
1. What characteristics of the Mississippi River contribute to the Dead Zone?
2. Is the dead zone in the Gulf of Mexico always present? Why or why not?
No, it is a seasonal event, driven by high nutrient inputs beginning in the spring. Fall
3. How would weather affect the dead zone in the Gulf of Mexico?
Rainfall patterns in the watershed would affect river discharge rates, nutrient patterns
4. What happens to the organisms in a dead zone?
As oxygen minimums are approached behaviors change. Organisms that can will move
worms.
5. Global climate change is predicted to increase rainfall in certain parts of the country and
decreased rainfall in others and contribute to an increase in ocean temperatures. How would
you expect this to affect the dead zone in the Gulf of Mexico? (hint check the predictions
available in Bates et al. 2008 http://www.ipcc.ch/pdf/technical-papers/climate-change-water-
en.pdf)
Rainfall in the watershed is predicted to be reduced so reduce river discharge will
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6. The Mississippi River watershed drains 41% of the contiguous United States, what would you
suggest would need to happen to reduce the Dead Zone in the Gulf of Mexico? What are
some of the challenges?
Answers will vary: