Transcript Cycles - Madeira City Schools

Cycles
Carbon and Nitrogen
Cycles
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.
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.
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.
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
Global Carbon Cycle
Carbon is exchanged between the active pools due to various processes
Π
photosynthesis and respiration between the land and the atmosphere, and
diffusion between the ocean and the atmosphere.
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