Transcript Document

THE 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 (78%), 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.
WHERE CAN YOU FIND IT?
Let's start with the main sources of nitrogen.
Nitrogen gas is the most abundant element
in our atmosphere.
The other main source of nitrogen is in the
nitrates of soil. The nitrogen in the
atmosphere cannot be used while the
nitrates in the soil can be used by plants.
Nitrogen can be converted into useful
nitrate compounds by bacteria, algae, and
even lightning. Once in the soil, the nitrogen
becomes biologically accessible.
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 compound that let
the plant survive. Organic compounds have carbon atoms. Those
compounds might be proteins, enzymes, or nucleic acids.
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.
Nitrogen is essential to all living systems, which makes the nitrogen cycle one of
Earth's most important nutrient cycles!!!
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
Harmful effects of nitrogen deposition
The 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.