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Human Alteration of the
Global Nitrogen Cycle

What is Nitrogen?
Nitrogen is the most abundant element in
the Earth’s atmosphere
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Nitrogen cannot be absorbed directly by
the plants and animals until it is converted
into compounds they can use
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Heather McGraw, Mandy Williams, Suzanne Heinzel, and Cristen Whorl, Give
SIUE Permission to Put Our Presentation on E-reserve at Lovejoy Library
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Step 2- Nitrification- Nitrification is the process which
converts the ammonia into nitrite ions which the plants can
take in as nutrients
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Step 4- Denitrification- Denitrification is the final step in
which other bacteria convert the simple nitrogen compounds
back into nitrogen gas (N2 ), which is then released back into
the atmosphere to begin the cycle again
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This includes byproducts of internal combustion
engines
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Removing nitrogen from the Earth’s crust and soil when we mine
nitrogen-rich mineral deposits
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Production and Use of
Nitrogen Fertilizers

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Nitrogen Fertilizer
#1 Contributor to new nitrogen in the
global cycle
First developed during WWI
Use has grown exponentially
Can actually increase the nitrogen so much
that soil fertility actually decreases

Nitrogen as Fertilizer
Nitrogen is found naturally in manures and other
organic fertilizers
Nitrogen is a key nutrient for plant growth
Four forms of nitrogen are used as fertilizer:
Nitrate
Ammonia
Ammonium
Urea

Problems with Nitrogen Fertilizers
Ammonia can escape into the air

The Need for Nitrogen
Plants lacking sufficient nitrogen become
yellow and stunted, with
smaller than average
flowers and fruits
Without nitrogen fertilizers,
an estimated one-third of our current
agricultural production would be lost
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Automobiles
Power Generation Plants
Industries

Internal Combustion Engines
Nitrogen oxides are formed in the
combustion process by oxidation of
nitrogen (from the atmosphere and fuel) to
NO and NO2

NOx Emission Control

Prevent formation in the cylinder
Remove from exhaust gases in an after-treatment
Most effective: introduction of water/steam because
it cuts the temperature peaks in the combustion
process
water-in-fuel emulsions
humidification of the combustion air
direct water injection into the combustion space

Subject of extensive development work by the
gas turbine manufacturers during the 1980s
Allowable NOx levels in dense cities are only
10 ppm by volume

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Acid Rain
Depositions of sulfur and nitrogen
Transport acid aerosols formed in the
atmosphere from a mixture of
hydrochloric, sulfuric, and nitric acid
Infiltrates soils, groundwater, rivers, and
lakes

What does all this mean?

Power Generation Plants

Industry

Impacts on the Atmosphere
Nitrous oxide contributes to overall
greenhouse warming
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Formation of photochemical (brown) smog
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We are greatly increasing the amount of nitrogen
cycling between the living world and the soil, water
and atmosphere
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This is having a serious impact on ecosystems
around the world
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Effects on the Ecosystem
Nitrogen saturation
Acidification of the soil
Increase in tree deaths
Reduction in overall species diversity
Loss of biodiversity
Acidification of lakes and streams
Eutrophication in estuaries and coastal waters

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For Further Information
Public Affairs Office
Ecological Society of America
This information was largely reproduced from the
“Human Alteration of the Global Nitrogen Cycle: Causes
And Consequences,” published by the Ecological Society of
America, in the journal Ecological Applications
(Volume 7, August 1997) with detailed citations to the
original scientific literature

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