1. Effect of anthropogenic nitrogen depositions on atmospheric CO2
Galina Churkina, Victor Brovkin, Werner von Bloh and Kristina Trusilova
MPI-BGC
PIK

2. Outline Nitrogen cycle – short introduction
Inputs
Distribution
Linkage to carbon cycle
What is the effect of increasing nitrogen deposition on atmospheric CO2?

3. Nitrogen Exchange in Ecosystems
Carbon Cycle: exchanges with a well-mixed atmospheric pool
Nutrient cycling: highly localized exchanges between plants, soils, and soil microbes
More than 90% of nitrogen absorbed by plants comes from recycling nutrients that were returned from vegetation to soils in previous years

4. Global Reactive Nitrogen Fixation
BNF – biological nitrogen fixation
(after Galloway et al. 2004)

5. Distributions of Inorganic Nitrogen Deposition
mgN/m2= 10-2kgN/ha
In early 1990s
(Galloway et al. 2004)

6. Is productivity of land ecosystems limited by nitrogen?
Yes, otherwise fertilizers would not be produced
Experiments with plants show clear N limitation
Reich et. al. PNAS, 1997.
R. Hakkenberg, in prep.

7. Increased productivity because of nitrogen fertilization?
Residual terrestrial carbon sink of PgC/yr – reasons unclear
Increased forest growth in Europe
Suggested carbon uptake due to increased atmospheric nitrogen deposition:
PgC/yr (Townsend et al 1996, Holland et al 1997)
0.25 PgC/yr (Nadelhoffer et al. 1999)

8. Is there effect of increasing nitrogen deposition on atmospheric CO2?

9. Model coupling Global NEP CO2 Climate anomalies
BIOME-BGC
CLIMBER-2
CO2
Forcing
(N depositions)
Forcing
(CO2
emissions)
Climate anomalies
BIOME-BGC provides land-atmosphere CO2 flux (NEP). CLIMBER-2 simulates oceanic CO2 uptake and climate change

10. Methods
BIOME-BGC- net fluxes of carbon from land to atmosphere (1°lat x1°lon)
Increasing nitrogen deposition (Dentener et al. 2006)
for from TM3
for from model ensemble
Increasing CO2 from CLIMBER
Climate
randomly shuffled NCEP climatology
anomalies for temperature, precipitation, and downward short-wave radiation from CLIMBER2

11. CLIMBER design
Climate simulations on very coarse spatial resolution (10°lat, 51°lon)
Observed CO2 emissions till 2000, SRES A2 emissions thereafter
With/without land use CO2 emissions
CO2 as the only GHG, no aerosols
Oceanic inorganic biogechemistry and marine biota model (Six and Maier-Reimer)
Global NEP from BIOME-BGC
Coupled climate-carbon cycle dynamics

12. Scenarios Scenario Climate change CO2 change
Nitrogen deposition change
Control No
CL_CO2
Yes
Nhigh
SRES A (Dentener et al., in press)
CO2_Nhigh
As above
CL_CO2_Nhigh
CL_CO2_Nlow
IIASA Maximum feasible reduction scenario 2030 (Dentener et al., in press)

13. Effects of CO2 and nitrogen deposition on global net carbon flux
CL_CO2_Nhigh
CO2_Nhigh
Nhigh
CL_CO2
Control

14. Effects of CO2 and nitrogen deposition on net carbon flux of Europe
CL_CO2_Nhigh
CO2_Nhigh
Nhigh
CL_CO2
Control

15. CO2 and nitrogen deposition effects on NEP are non-linear
Change in global NEP, PgC/yr
Change in European NEP, PgC/yr
CO2+Ndep
1.2 (100%)
0.13 (100%)
N dep
0.55 (46%)
0.09 (68%)
CO2
0.25 (21 %)
0.016 (12%)
Synergetic
0.39 (33 %)
0.025 (20%)

18. Conclusions
Increased nitrogen deposition increases significantly land carbon uptake
CO2 and nitrogen deposition effects on NEP are non linear
Nitrogen deposition results in ~ 30 ppm lower atmospheric CO2 in 2030

19. Perspectives
Changes in nitrogen deposition in the future (after 2030)- to investigate changes in climate system
Introduce dynamic biological nitrogen fixation in BIOME-BGC
Compare current results to measurements such as forest inventories, etc.
Can increases in lightning frequency lead to higher nitrogen inputs?