Download Accel N2 Cycle Qs ANSWERS

Nitrogen Cycle Questions (use supplementary readings to answer)
ANSWERS
Note: These answers should come from a synthesis of a variety
of sources - your notes, text reading, class discussion, and
especially your reading of the four articles I posted on the class
website. Some questions can be answered from looking at just
one of these sources, but some questions required you to draw
from several of these sources simultaneously.
1. Why do living things require nitrogen?
Living things require nitrogen to make proteins (& DNA).
2. Where is the majority of nitrogen found in the global cycle?
The majority of nitrogen is found in the air as nitrogen gas.
3. To what must gaseous nitrogen be converted before it can be used by plants and
animals?
Nitrogen gas must be converted to ammonium or nitrate before it can be
used by plants. It must be converted to proteins before it can be used by
animals.
4. What are the ways in which atmospheric nitrogen can be converted to useful nitrates?
Nitrogen gas is converted to nitrates by nitrogen fixation followed by
nitrification.
5. Where can we find nitrogen-fixing bacteria?
Nitrogen-fixing bacteria are found in the soil and in legume root nodules.
6. How do plants use the nitrates?
Plants use nitrates to make their proteins.
7. How do animals get their nitrogen?
Animals get their nitrogen by eating plant and animal proteins.
8. What happens to the nitrogen in the plant or animal when the organism dies? To what
is it converted?
Plant & animal proteins are decomposed to ammonium when the organisms
die.
9. Describe the process by which ammonium becomes helpful nitrate again.
Ammonium is converted to nitrate in the process of nitrification.
10. By what process(es) is nitrogen released into the atmosphere as gaseous N2?
Nitrogen is converted from nitrate to nitrogen gas in de-nitrification. No, this
is not a common pathway.
11. What are the issues (causes/effects) associated with raising livestock and poultry on
an industrial scale?
• In industrial scale livestock operations, more waste is produced by livestock
than can easily and safely be disposed of. Traditionally livestock waste was
used to fertilize nearby fields, but large-scale livestock operations no longer
•
•
•
make this feasible, as there is too much waste to possibly use in this
manner.
Spillage from waste lagoons can contaminate groundwater and nearby water
bodies with nitrates and ammonia, causing a eutrophic system in which
dissolved oxygen levels fall and large numbers of fish and other aquatic
organisms are asphyxiated.
Waterways can also be contaminated with fecal pathogens from spilled
untreated waste (harmful bacteria and protists), which people could then
come into contact with by fishing or swimming in those waters.
Ammonia that evaporates from waste lagoons and fields sprayed with
livestock waste can also be an air pollutant, which then is re-deposited on
land via precipitation, perpetuating aquatic and terrestrial eutrophication.
12. What do human population, consumption and technology have to do with hogs?
As human population has increased, so has the need for food to support our
population growth. Traditional organic farming is not efficient enough to
provide enough food for our (still growing) human population. The
discovery and refinement of the Haber-Bosch synthesis of ammonia from
molecular nitrogen made enormous increases in agricultural productivity
possible. As fertilizer production became more prevalent globally, food
production increases followed, as did human population increases.
Furthermore, many countries developed a preference and appetite for
protein-rich meat, which is ecologically expensive to produce. The highprotein diet that many countries enjoy today would not be possible without
greater agricultural productivity to support it.
13. What is the ecological significance of eating mainly meat rather than vegetables and
grains?
By eating higher up on the food chain, humans need 10x more plants
(vegetables and grains) to support themselves than if they ate plants
directly. This is because raising grains to feed livestock to feed humans
means 90% of the plant energy is used by the livestock in their
metabolism/cell respiration.
14. Why is animal waste in water a problem? Is it the only problem?
The nitrates in the waste lead to eutrophication and the death of aquatic
organisms. No, this is not the only problem. Contamination with fecal
pathogens is also a potential problem (see answer to question 11).
15. What happens if excess nitrogen and phosphorus enters lakes, streams, and rivers?
Algae blooms occur, as these formerly limiting nutrients (nitrogen and
phosphorus) become abundant in the aquatic ecosystem.
16. What happens when algae die en masse?
Large amounts of dead algae feed (overfeed) the decomposing microbes or
bacteria in bodies of water. The population of these decomposers then
increases greatly, and they outcompete other aquatic organisms for
dissolved oxygen (DO) in the water. DO levels drop as a result of heavy
intake by decomposers, and other aquatic organisms are left to
suffocate/asphyxiate in the water.
17. Who/what is mostly responsible for eutrophication? Is it heavy industry? Individuals?
Someone/something else? What should be done about it, if anything?
Answers will vary… You could cite poor regulation of factory farms, overconsumption of meat by humans, poor safety practices of factory farms, etc.
18. Is eutrophication really a serious problem? Why or why not?
Yes. We have an appetite for fertilizers that is not sustainable, much like our
appetite for fossil fuels. The wide-spread disruption of ecosystems,
especially aquatic ecosystems, through eutrophication decreases
biodiversity and accelerates system destabilization.
(Additional evidence & elaboration possible)
19. Do you see any signs of eutrophication near where you live? If so, what are the
sources?
Answers will vary. May include fertilizer run-off from suburban landscaping
or agriculture.
20. What is the difference between point and non-point sources of pollution? (you would
have to look this up if you did not infer the meaning from the articles)
Point source pollution: the origin of the pollution is known (and is a single
source).
Non-point source pollution: the origin of the pollution is non-specific
(typically multiple sources, possibly distant and hard to identify).
21. If the projected human population increase to about 10 billion during the next century
proves true, what are the implications for aquatic and terrestrial ecosystems,
agriculture, etc?
If this population growth proves true AND we do not take any steps to
change our current practices around fertilizer use and application, livestock
waste management, or even our dietary choices, then the implications for
ecosystems and agriculture will be very serious. Pollution with excess
nitrates and ammonia will take it's toll on ecosystems and our appetite for
fertilizer will greatly increase to force enough agricultural productivity to
meet skyrocketing human population demands.
Article 1:
"Global Population and the Nitrogen Cycle" by Vaclav Smil. Scientific American.
July 1997, pp. 76-81.
Article 2:
Eutrophication from Wikipedia. http://en.wikipedia.org/wiki/Eutrophication
Article 3:
Livestock Legacy from a journal published by the Nat. Inst. of Env. Health Sci.
Article 4:
Nutrient Overload: Unbalancing the Global Nitrogen Cycle from the World Resources
Institute.