View
220
Download
0
Tags:
Embed Size (px)
Citation preview
Human Disruption of the Global Nitrogen Cycle
Alan Townsend
7 December 2007
Guest Lecture – Soils Geography
University of Colorado, Boulder
Simplified Terrestrial N Cycle
Soil Organic Matter (SOM)
Plants
NH4 NO3
Mineralization
Leaching to groundwater and streams
NO, N2O NO, N2O, N2
N2
Simplified Global N Cycle
Nitrogen Transformation Cycle: Past
N2
Lig
htn
ing
N-F
ixati
on
Den
itri
fica
tion
Reactive N
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
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
Timing of N Cycle Changes
A global-scale change, but not equally distributed
Annual Nitrogen Deposition(a map of fertilizer use would look about the same…)
Why is N Use Increasing?
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
Fertilizer Consumption - last 50 years
• 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
Trends in N Deposition
Sources of N – Northeastern US
Boyer et al, 2002
Fates of N – NE US
Van Breemen et al, 2002
What goes in, comes out…NE US
N Losses Correlate with Anthropogenic N Inputs
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)
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Stevens et al, Science 2004
N regulation
IPCC