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 Soil Organic Matter (SOM) Plants NH 4 NO 3 Mineralization Leaching to groundwater and streams NO, N 2 O NO, N 2 O, N 2 N2N2

3. Simplified Global N Cycle

4. Nitrogen Transformation Cycle: Past N2N2 Lightning N-Fixation Denitrification Reactive N

5. Nitrogen Transformation Cycle: Present N2N2 Lightning N-Fixation Denitrification Reactive N N 2 +3H 2 2NH 3 N 2 + O 2 NO y Legumes

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. 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 N 2 to NH 3 (won the Nobel prize in 1918). This is still how fertilizer is produced

11. Fertilizer Consumption - last 50 years

12. 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

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 O 3 ) Stratospheric ozone depletion Species composition (including feedbacks with invasives)

20. Stevens et al, Science 2004

21. N regulation IPCC