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

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

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

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

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

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.

Increased productivity because of nitrogen fertilization? Residual terrestrial carbon sink of 1.5-1.9 PgC/yr – reasons unclear Increased forest growth in Europe Suggested carbon uptake due to increased atmospheric nitrogen deposition: 0.1-2.3 PgC/yr (Townsend et al 1996, Holland et al 1997) 0.25 PgC/yr (Nadelhoffer et al. 1999)

Is there effect of increasing nitrogen deposition on atmospheric CO2?

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

Methods BIOME-BGC- net fluxes of carbon from land to atmosphere (1°lat x1°lon) Increasing nitrogen deposition (Dentener et al. 2006) for 1860-1999 from TM3 for 2000-2030 from model ensemble Increasing CO2 from CLIMBER Climate randomly shuffled NCEP 1948-1952 climatology anomalies for temperature, precipitation, and downward short-wave radiation from CLIMBER2

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

Scenarios Scenario Climate change CO2 change Nitrogen deposition change Control No CL_CO2 Yes Nhigh SRES A2 2030 (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)

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

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

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%)

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

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?