THE NITROGEN CYCLE

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THE NITROGEN CYCLE

• Nitrogen (N) is an element like carbon.
• All creatures need nitrogen to survive.
• There are huge amounts of nitrogen gas (N2) in
  the atmosphere, but most animals and plants have
  no way of using it. It needs to be fixed (put
  into a biologically useful compound). After it is
  fixed, it can then start to move through the
  cycles and organisms in an ecosystem.

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WHERE CAN YOU FIND IT?

• Let's start with the main sources of nitrogen.
  Nitrogen gas is the most abundant element in our
  atmosphere (78). The nitrogen in the atmosphere
  cannot be used by living organisms. Nitrogen can
  be converted into useful nitrate compounds by
  Nitrogen Fixing bacteria, algae, and even
  lightning. Once in the soil, the nitrogen becomes
  biologically accessible.

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BORROWING NITROGEN

• Plants are the main users of nitrogen in the
  soil. They are able to take in the nitrates
  through their root system.
• Once inside the plant, the nitrates are used in
  organic compounds such as amino acids that let
  the plant survive.
• Once the plants have converted the nitrogen, the
  element can be returned to the soil or taken up
  by animals.
• Herbivores eat plants and convert many of the
  amino acids into new proteins.
• Omnivores that eat both plants and animals are
  able to take in the nitrogen rich compounds as
  well.
• The nitrogen compounds are only borrowed.
  Nitrogen atoms are returned to the soil in poop
  and dead organisms. Once in the soil, the whole
  process can start again.

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Nitrogen is essential to all living systems,
which makes the nitrogen cycle one of Earth's
most important nutrient cycles. 78 of Earth's
atmosphere is made up of nitrogen in its gas
phase. Atmospheric nitrogen becomes part of
living organisms in two ways. The first is
through bacteria in the soil that form nitrates
out of nitrogen in the air. The second is through
lightning. During electrical storms, large
amounts of nitrogen are oxidized and united with
water to produce an acid that falls to Earth in
rainfall and deposits nitrates in the soil.
Plants take up the nitrates and convert them to
proteins that then travel up the food chain
through herbivores and carnivores. When organisms
excrete waste, the nitrogen is released back into
the environment. When they die and decompose, the
nitrogen is broken down and converted to ammonia.
Plants absorb some of this ammonia the remainder
stays in the soil, where bacteria convert it back
to nitrates. The nitrates may be stored in humus
or leached from the soil and carried into lakes
and streams. Nitrates may also be converted to
gaseous nitrogen through a process called
denitrification and returned to the atmosphere,
continuing the cycle.
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Human activities and the nitrogen cycle Human
activities cause increased nitrogen deposition in
a variety of ways, including burning of both
fossil fuels and forests, which releases nitrogen
into the atmosphere fertilizing crops and golf
courses with nitrogen-based fertilizers, which
then enter the soil and water ranching, during
which livestock waste releases ammonia into the
soil and water allowing sewage and septic
tanks to leach into streams, rivers, and
groundwater
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Harmful effects of nitrogen depositionThe
consequences of human-caused nitrogen deposition
are profound and influence many aspects of the
Earth system, including

• ecosystems Nitrogen additions to the soil can
  lead to changes that favor weeds over native
  plants, which in turn reduces species diversity
  and changes ecosystems. Research shows that
  nitrogen levels are linked with changes in
  grassland species, from mosses and lichens to
  grasses and flowers.
• precipitation Nitrogen oxides react with water
  to form nitric acid, which along with sulfur
  dioxide is a major component of acid rain. Acid
  rain can damage and kill aquatic life and
  vegetation, as well as corrode buildings,
  bridges, and other structures.
• air quality High concentrations of nitrogen
  oxides in the lower atmosphere are a precursor to
  tropospheric ozone which is known to damage
  living tissues, including human lungs, and
  decrease plant production.
• water quality Adding large amounts of nitrogen
  to rivers, lakes, and coastal systems results in
  eutrophication, a condition that occurs in
  aquatic ecosystems when excessive nutrient
  concentrations stimulate blooms of algae that
  deplete oxygen, killing fish and other organisms
  and ruining water quality. Parts of the Gulf of
  Mexico, for example, are so inundated with excess
  fertilizer that the water is clogged with algae,
  suffocating fish and other marine life.
• carbon cycle The impacts of nitrogen deposition
  on the global carbon cycle are uncertain, but it
  is likely that some ecosystems have been
  fertilized by additional nitrogen, which may
  boost their capture and storage of carbon.
  Sustained carbon sinks are unlikely, however,
  because soil acidification, ozone pollution, and
  other negative effects eventually compromise
  nitrogen-enhanced carbon uptake.