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Human Disruption of the Global Nitrogen Cycle

Human Disruption of the Global Nitrogen Cycle. Alan Townsend 7 December 2007 Guest Lecture – Soils Geography University of Colorado, Boulder. Simplified Terrestrial N Cycle. N 2. Plants. Soil Organic Matter (SOM). NO, N 2 O. NO, N 2 O, N 2. Mineralization. NH 4. NO 3.

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Human Disruption of the Global Nitrogen Cycle

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  1. Human Disruption of the Global Nitrogen Cycle Alan Townsend 7 December 2007 Guest Lecture – Soils Geography University of Colorado, Boulder

  2. Simplified Terrestrial N Cycle N2 Plants Soil Organic Matter (SOM) NO, N2O NO, N2O, N2 Mineralization NH4 NO3 Leaching to groundwater and streams

  3. Simplified Global N Cycle

  4. Nitrogen Transformation Cycle: Past N2 Lightning N-Fixation Denitrification Reactive N

  5. Nitrogen Transformation Cycle: Present N2 Lightning N-Fixation Legumes Denitrification N2 + O2 NOy N2+3H2 2NH3 Reactive N

  6. 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

  7. Timing of N Cycle Changes

  8. A global-scale change, but not equally distributed Annual Nitrogen Deposition (a map of fertilizer use would look about the same…)

  9. Why is N Use Increasing?

  10. 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

  11. Fertilizer Consumption - last 50 years

  12. N and Agricultural Ecosystems • 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

  13. Trends in N Deposition

  14. Sources of N – Northeastern US Boyer et al, 2002

  15. Fates of N – NE US Van Breemen et al, 2002

  16. What goes in, comes out…NE US

  17. N Losses Correlate with Anthropogenic N Inputs

  18. 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)

  19. Stevens et al, Science 2004

  20. N regulation IPCC

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