Cycles of the Earth
&
Biogeochemical Cycles
Dead Zone
Slides 122-136
Humans affect the nitrogen cycle
• Haber-Bosch process = production of fertilizers by
combining nitrogen and hydrogen to synthesize
ammonia
– Humans overcame the limits on crop productivity
• Fixing atmospheric nitrogen with fertilizers
– Increases emissions of greenhouse gases and smog
– Washes calcium and potassium out of soil
– Acidifies water and soils
– Moves nitrogen into terrestrial systems and oceans
– Reduces diversity of plants adapted to low-nitrogen
soils
– Changed estuaries and coastal ecosystems and
fisheries
Humans affect the phosphorus
cycle
• Mining rocks for fertilizer moves phosphorus
from the soil to water systems
• Wastewater discharge also releases
phosphorus
• Runoff containing phosphorus causes
eutrophication of aquatic systems
– Produces murkier waters
– Alters the structure and function of aquatic
systems
– Do not buy detergents that contain phosphate
Solutions to the dead zone
• The Harmful Algal Bloom and Hypoxia
Research and Control Act (1998)
– Called for an assessment of hypoxia in the dead
zone
• Solutions outlined included:
– Reduce nitrogen fertilizer use in Midwestern
farms
– Apply fertilizer at times which minimize runoff
– Use alternative crops and manage manure better
– Restore wetlands and create artificial ones
– Improve sewage treatment technologies
– Evaluate these approaches
Central Case: The Gulf of Mexico’s “Dead Zone”
• Gulf of Mexico brings in 600
million kg/year shrimp, fish,
and shellfish
• Gulf “dead zone” = a region
of water so depleted of
oxygen that kills or drives
away marine organisms
• Hypoxia = low
concentrations of dissolved Dead Zones Part 1
oxygen water
Dead Zones part 2
• Caused by fertilizer, runoff,
'Dead Zones' Are Increasing in Our
sewage
Oceans WORLDWIDE!
QUESTION: Review
The term “system” includes all of the
following, except:
a) A network of relationships among various
components
b) The various components tend to minimize
interactions
c) Energy, matter, and information are
exchanged between components
d) Energy and matter are valuable inputs to the
system
QUESTION: Review
Which of the following describes a positive
feedback loop?
a) It drives a system towards an extreme
b) It stabilizes the system
c) It causes the system to move in opposite
directions at the same rates
d) It causes the system to maintain a constant
condition
QUESTION: Review
Which of the following is a correct statement?
a) Energy and matter flow in one direction only
b) Energy and matter both cycle repeatedly
c) Energy flows in one direction, while matter
recycles
d) Matter flows in one direction, while energy
recycles
QUESTION: Review
What is the definition of “net primary
production”?
a) Assimilation of energy by heterotrophs
b) Elements and compounds that are required
for survival
c) Energy remaining after respiration that is
used to generate biomass
d) Assimilation of energy by autotrophs
QUESTION: Review
Which biogeochemical cycle comprises 78%
of our atmosphere, and is contained in
proteins, DNA and RNA?
a)
b)
c)
d)
Carbon
Nitrogen
Water
Phosphorus
QUESTION: Review
Which biogeochemical cycle is being affected
by damming rivers, and altering the
surface and vegetation?
a)
b)
c)
d)
Carbon
Nitrogen
Water
Phosphorus
QUESTION: Review
Which rock is formed from magma; for
example, granite and basalt?
a)
b)
c)
d)
Sedimentary
Igneous
Metamorphic
Phosphorus
QUESTION: Weighing the
Issues
Who should pay for cleanup of the nitrate
entering the Gulf of Mexico?
a)
b)
c)
d)
The federal government
State governments
Fishermen
Farmers responsible for fertilizer runoff
Decreasing pollution
• Scientists, farmers and
policymakers are encouraged to
– Decrease fertilizer use
– While safeguarding agriculture
• Offering insurance and
incentives
• Using new farming methods
• Planting cover crops
• Maintaining wetlands
• There have been some
successes
– Despite a lack of funding