Cycles

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Cycles

• Carbon and Nitrogen
• Cycles

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Nitrogen cycle

• THE NITROGEN CYCLE Nitrogen (N) is an element
  like carbon. All creatures need nitrogen to
  survive. There are huge amounts of nitrogen gas
  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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• Nitrogen is essential to all living systems,
  which makes the nitrogen cycle one of Earth's
  most important nutrient cycles.
• Eighty percent 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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• Nitrogen is essential to all living systems,
  which makes the nitrogen cycle one of Earth's
  most important nutrient cycles.
• Eighty percent 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 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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