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Insights Into Human Disruption of Nitrogen Cycle

Understand the impact of human activity on the global nitrogen cycle. Learn the past and present nitrogen transformation cycles, fertilizer consumption trends, environmental effects, and regulation. Explore the factors driving the increasing use of nitrogen and the implications for ecosystems. Discover how human interventions have altered the natural nitrogen cycle dynamics.

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Insights Into Human Disruption of 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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