14 - NITROGEN DEPOSITION READINGS FREEMAN 2005 Chapter 54...

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NITROGEN DEPOSITION READINGS: FREEMAN, 2005 Chapter 54 Pages 1257-1258
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NITROGEN DEPOSITION Nitrogen deposition refers to the addition of anthropogenic atmospheric nitrogen to ecosystems. Current rates of deposition in the US and Europe can be 10-50 times above historic levels. Because many ecosystems are N limited, this new source of fertilization can alter community structure and function. The potential impact of N deposition on native plant species and ecosystems is an active area of ecological research.
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GLOBAL NITROGEN CYCLE (I) 99.4% of exchangeable N is found in the atmosphere; 0.5% is dissolved in the ocean; 0.04% in detritus ; 0.006% as inorganic N sources; 0.0004% in living biota. Figure 54.19 in Freeman (2005) gives some pathways and rates of exchange.
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GLOBAL NITROGEN CYCLE (II) Human activities have doubled the rate of nitrogen entering the land-based nitrogen cycle, and the rate is climbing. Nitrogen is a limiting factor in population dynamics, plant productivity, carbon cycling and maintaining plant diversity. Excess nitrogen addition can pollute ecosystems and alter community structure and function.
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SOURCES OF “FIXED” NITROGEN Human-derived sources of nitrogen surpass natural sources and are increasing. A major part of fixed nitrogen ends up on land; some of which gets back into the atmosphere only to return during rainfall. The return of largely human derived sources of nitrogen to land is called nitrogen deposition. Galloway et al, 2003
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Primary Sources of Nitrogen Addition to the Atmosphere Domestic animals are the source of around 43% of atmospheric ammonia. Fossil fuel combustion accounts for 46% of atmospheric oxides of nitrogen (N 2 O, NO and NO 2 ). The trends shown for Switzerland are characteristic of many developed countries.
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Sources of Nitrogen Emissions from Fossil Fuels Among the fossil fuel sources, power plants, automobiles and industry are the primary sources of atmospheric nitrogen emissions in the US. Nitrous oxide is the only one that stays in the atmosphere for significant time.
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Sources of Nitrogen Emissions in Urban Areas Vehicles are the primary source of nitrogen emissions in cities. Coal fired power plants are also major contributors. Heavy industry such as steel mills is an important source.
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Precipitation Removes Ammonium and Nitrates from the Air Over 130 gigitons of N deposition are removed from the atmosphere each year by precipitation on land. 70% came from human- derived sources. The three largest sources are domestic animals, fossil fuels and fertilizers applied to fields. 1 gigaton (Gt) = 10 6 grams
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Ammonium Deposition in the United States Livestock, unplowed soils and fertilizers account for 68% of the ammonium released into the atmosphere. Precipitation removes it rapidly
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This note was uploaded on 04/02/2009 for the course CHEM 112 taught by Professor Jursich during the Spring '08 term at Ill. Chicago.

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14 - NITROGEN DEPOSITION READINGS FREEMAN 2005 Chapter 54...

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