Human Disruption of the Global Nitrogen Cycle Alan Townsend 7 December 2007 Guest Lecture – Soils...
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![Page 1: Human Disruption of the Global Nitrogen Cycle Alan Townsend 7 December 2007 Guest Lecture – Soils Geography University of Colorado, Boulder.](https://reader030.fdocuments.net/reader030/viewer/2022032704/56649d4e5503460f94a2d0c5/html5/thumbnails/1.jpg)
Human Disruption of the Global Nitrogen Cycle
Alan Townsend
7 December 2007
Guest Lecture – Soils Geography
University of Colorado, Boulder
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Simplified Terrestrial N Cycle
Soil Organic Matter (SOM)
Plants
NH4 NO3
Mineralization
Leaching to groundwater and streams
NO, N2O NO, N2O, N2
N2
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Simplified Global N Cycle
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Nitrogen Transformation Cycle: Past
N2
Lig
htn
ing
N-F
ixati
on
Den
itri
fica
tion
Reactive N
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Nitrogen Transformation Cycle: Present
N2
Lig
htn
ing
N-F
ixati
on
Den
itri
fica
tion
Reactive N
N2+3H2 2NH3N2 + O2 NOyLe
gu
mes
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Nr Creation by Nature and Humans
•Since 1960:• Flows of biologically
available nitrogen in terrestrial ecosystems doubled
• > 50% of all the synthetic nitrogen fertilizer ever used has been used since 1985
• Humans produce as much biologically available N as all natural pathways and this may grow a further 65% by 2050
Human-produced Reactive Nitrogen
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Timing of N Cycle Changes
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A global-scale change, but not equally distributed
Annual Nitrogen Deposition(a map of fertilizer use would look about the same…)
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Why is N Use Increasing?
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Why is N Use Increasing?
Agricultural Use: Fertilizers (and especially N) increase yields: global use was 14 million tons in 1950 and about 135 tons now.
Fritz Haber (the Haber process) created a method for converting N2 to NH3 (won the Nobel prize in 1918). This is still how fertilizer is produced
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Fertilizer Consumption - last 50 years
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• Haber-Bosch has facilitated agricultural intensification
• 40% of world’s population is alive because of it
• An additional 3 billion people by 2050 will be sustained by it
• Most N that enters agroecosystems is released to the environment
N and Agricultural Ecosystems
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Trends in N Deposition
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Sources of N – Northeastern US
Boyer et al, 2002
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Fates of N – NE US
Van Breemen et al, 2002
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What goes in, comes out…NE US
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N Losses Correlate with Anthropogenic N Inputs
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Environmental Effects of a Changing Global N Cycle (the short list…)
• Climate
• Acid rain
• Water quality
• Coastal eutrophication
• Air quality (e.g. tropospheric O3)
• Stratospheric ozone depletion
• Species composition (including feedbacks with invasives)
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Stevens et al, Science 2004
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N regulation
IPCC