The Carbon Cycle
Disrupting the Carbon Cycle
The level of carbon dioxide in the atmosphere has remained fairly constant over
Earth as a whole. The balance can be changed if large amounts of carbon are
removed from or added to parts of the carbon cycle. See. Figure 2.5 on page 47 with
respect to the Carboniferous Period.
The Nitrogen Cycle
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Nitrogen Fixation: How do plants obtain their nitrogen? Earth’s atmosphere
is nearly 80% nitrogen gas (N2), but most organisms cannot absorb nitrogen
directly from the air. In order to be used by organisms, nitrogen atoms (like
carbon atoms) must first be “fixed”: pulled from the air and bonded to other
elements to make new compounds. Nitrogen can combine with hydrogen to
form ammonium (NH4). Nitrogen can combine with oxygen to form nitrate
(NO3). Examples: nitrogen-fixing bacteria.
Nitrification: Ammonia is converted back into nitrates by nitrifying bacteria.
Denitrification: To complete the cycle, nitrates in the soil or water may be
converted back into nitrogen gas by denitrifying bacteria.
Human Impacts on the Nitrogen Cycle
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Farmers used artificial fertilizers to grow more crops for a rapidly expanding
human population.
Fossil fuels (example: burning of gas for cars) being burned enter the
atmosphere and fall back on Earth.
This results in nitrogen overload
o Effects on Soil: serious chemical changes in the soil don't allow for
plants to grow the way they should. Extra nitrogen damages tree roots
and stunts tree growth because of soil acidity. High acidity kills
bacteria that help absorb essential minerals.
o Effects on the Atmosphere: Nitric acid is formed from the burning of
fossil fuels. This is a component of acid rain or snow. How does acid
rain affect affects plants and animals? One solution is to neutralize the
acid by adding limestone (to lakes for example).
o Effects on Fresh-Water Ecosystems: The increase of nitrates allow for
rapid growth of algae and weeds in lakes and streams. In drinking
water, nitrates can enter from the soil into ground water and are
converted into nitrites in our stomachs. This reduces the ability of the
blood to carry oxygen throughout the body (anemia).
o Effects on Biodiversity: Biodiversity is the measure of the variety of
species on Earth. When nitrogen fertilizers were first used in
grasslands, only a few grasses were able to use the extra nitrogen and
increase their growth. These grasses became dominant while others
became rare or disappeared. Fewer plant species decreases the
number of species of animals and micro-organisms that depend on
them.
Sustainable Development: development that meets the needs of the present time
without compromising the ability of future generations to meet their own needs.