Changes in the Global Nitrogen Cycle: Causes and Consequences

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Changes in the Global Nitrogen Cycle Causes and
Consequences

• Taken largely from
• Human Alteration of the Global Nitrogen
  CycleCauses and Consequences
• Issues in Ecology Number 1 Spring 1997
• by
• Peter M. Vitousek, Chair, John Aber, Robert W.
  Howarth,
• Gene E. Likens, Pamela A. Matson, David W.
  Schindler,
• William H. Schlesinger, and G. David Tilman

http//www.esa.org/science_resources/issues/FileEn
glish/issue1.pdf
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Understanding element cycles as part of the major
functioning of ecosystems, requires following a
specific "approach".

• 1st - Accounting Accounting tells you "where
  things are", or the distribution of the element
  in different pools within the ecosystem. 
• 2nd - Cycling Cycling tells you "where things
  are going", and how fast they are moving from
  different pools in the ecosystem. 
• 3rd - Controls Determining the controls tells
  you "how does the system function, and what
  factors drive the cycling". 

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The nitrogen (N) cycle is a manifestation of
oxidation and reduction reactions - the loss and
gain of electrons. Oxidation and reduction
reactions are also the hallmark of the
biogeochemical cycling of carbon (C), hydrogen
(H), and oxygen (O) the chemical elements with
which the N cycle is most commonly and intimately
interconnected.
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The impacts of human domination of the nitrogen
cycle that we have identified with certainty
include

• Increased global concentrations of nitrous
  oxide (N2O), a potent greenhouse gas, in the
  atmosphere as well as increased regional
  concentrations of other oxides of nitrogen
  (including nitric oxide, NO) that drive the
  formation of photochemical smog
• Losses of soil nutrients such as calcium and
  potassium that are essential for long-term soil
  fertility
• Substantial acidification of soils and of the
  waters of streams and lakes in several regions
• Greatly increased transport of nitrogen by
  rivers into estuaries and coastal waters where it
  is a major pollutant.

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Human alterations of the nitrogen cycle have

• Accelerated losses of biological diversity,
  especially among plants adapted to low-nitrogen
  soils, and subsequently, the animals and microbes
  that depend on these plants
• Caused changes in the plant and animal life and
  ecological processes of estuarine and nearshore
  ecosystems, and contributed to long-term declines
  in coastal marine fisheries.

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http//bcs.whfreeman.com/thelifewire/content/chp58
/5802004.html
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Nitrogen once upon a time
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Nitrogen Fixation

• Global sources of biologically available (Fixed)
  nitrogen)
• ANTHROPOGENIC SOURCES
• ANNUAL RELEASE OF FIXED NITROGEN (teragrams)
• Fertilizer 80
• Legumes and other plants 40
• Fossil fuels 20
• Biomass burning 40
• Wetland draining 10
• Land clearing 20
• Total from human sources 210
• NATURAL SOURCES
• Soil bacteria, algae, lightning, 140

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• Nitrous Oxide is
• a very effective heat-trapping gas in the
  atmosphere
• unreactive and long lived in the lower atmosphere
• in the stratosphere it can trigger reactions that
  deplete and thin the stratospheric ozone layer
• increasing steadily, but source is still not
  completely identified

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• Nitric Oxide (80 from human activities)
• highly reactive in the lower atmosphere and
  therefore much shorter lived.
• catalyzing force in the formation of
  photochemical (or brown) smog.
• In the presence of sunlight,nitric oxide and
  oxygen react with hydrocarbons emitted by
  automobile exhausts to form ozone, the most
  dangerous component of smog.
• Ground-level ozone has serious detrimental
  effects on human health as well as the health and
  productivity of crops and forests.
• Nitric oxide, along with other oxides of nitrogen
  and sulfur, can be transformed in the atmosphere
  into nitric acid and sulfuric acid, which are the
  major components of acid rain.

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• Ammonia (70 from human activity)
• acts as the primary acid-neutralizing agent in
  the atmosphere, having an opposite influence on
  the acidity of aerosols, cloudwater, and
  rainfall.
• May have important role in missing carbon or ??
• Nitrogen saturation and
• Soil acidification and release of nutrients
• Marked reduction in overall species diversity as
  the few plant species adapted to take full
  advantage of high nitrogen out compete their
  neighbors.

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Nitrogen in Aquatic Systems

• Adding inorganic nitrogen to freshwater
  ecosystems that are also rich in phosphorus can
  eutrophy as well as acidify the waters.
• Both eutrophication and acidification generally
  lead to decreased diversity of both plant and
  animal species.
• When high nitrogen loading causes eutrophication
  in stratified waters where a sharp temperature
  gradient prevents mixing of warm surface waters
  with colder bottom waters the result can be
  anoxia (no oxygen) or hypoxia (low oxygen) in
  bottom waters.

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Effects of Nitrates, Nitrogen and Ammonia

• Methemoglobinemia
• Acidification
• Eutrophication ? anoxia in stratified waters
• Toxic algal blooms

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Some facts

• The process of manufacturing fertilizer by
  industrial nitrogen fixation was first developed
  in Germany during World War I.
• Fertilizer production has grown exponentially
  since the 1940s.
• The amount of industrially fixed nitrogen applied
  to crops during the decade from 1980 to 1990 more
  than equaled all industrial fertilizer applied
  previously in human history.

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More facts

• The momentum of human population growth and
  increasing urbanization ensures that industrial
  fertilizer production will continue at high and
  likely accelerating rates for decades in order to
  meet the escalating demand for food.

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Crops

• Soybeans, peas, alfalfa, and other leguminous
  crops and forages.
• Non-leguminous, non-fixers rice
• Huge demand for soybeans for animal feed

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The Future

• In fact, global nitrogen deposition may as much
  as double in the next 25 years as agriculture and
  energy use continue to intensify

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What needs to be done

• National and international policies should
  attempt to reduce these impacts through the
  development and widespread dissemination of more
  efficient fossil fuel combustion technologies and
  farm management practices that reduce the
  burgeoning demand for and release of nitrogenous
  fertilizers.

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What you can focus on

• Consumers can also contribute substantially to
  closing the open loop which currently allows
  nitrogen to be deposited on the land, washed into
  water courses and flushed out to sea.

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Accounting for the N stocks, flows, and controls
in the food stream
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Accounting for N Flows
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Understanding element cycles as part of the major
functioning of ecosystems, requires following a
specific "approach".

• 1st - Accounting Accounting tells you "where
  things are", or the distribution of the element
  in different pools within the ecosystem. 
• 2nd - Cycling Cycling tells you "where things
  are going", and how fast they are moving from
  different pools in the ecosystem. 
• 3rd - Controls Determining the controls tells
  you "how does the system function, and what
  factors drive the cycling".