Nitrogen Controls on Carbon Sequestration by G3gt67

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									Nitrogen Controls on Carbon
       Sequestration

 J. Melillo1, D. Kicklighter1, H. Tian1,
 A. McGuire2, J. Clein2, B. Moore III3
              [jmelillo@mbl.edu]
        1 Marine Biological Laboratory

             2 University of Alaska

        3 University of New Hampshire
The Global Nitrogen (N) Cycle and Carbon
              Sequestration
Fact:
• Humans have more than doubled the rate at which reactive
  N is added to the biosphere annually.
Fact:
• Through fertilizer production, the planting of legumes, and
  high temperature combustion, humans transform about
  150 TgN annually from unreactive N to reactive N.
Fact:
• A fraction of this reactive N enters ecosystems in which
  carbon sequestration is N limited.
Question:
• Is N-stimulated carbon sequestration currently a significant
  component of the global carbon budget?
               Approach

• We used a process-based
  biogeochemistry model running with an
  open N cycle to estimate the annual N-
  stimulated carbon sequestration rate in
  North America.
• The current spatially explicit N-
  deposition pattern for the region was
  estimated using the results of Dentner
  and Crutzen.
Nitrogen Deposition in North America (>150N)
      Annual N-deposition Rates
              Tg N/yr

                All land   Forest only

North America     7.3          3.2
USA               4.8          1.9
Canada            1.8          1.1
Other             0.7          0.2
          N-Stimulated Carbon Storage




g C /m2 /yr
                                            400
                                            350
                                            300




                                Tg C yr-1
                                            250
                                            200
                                            150
                                            100
                                             50
                                              0
            400
            350
                                                  North America
            300
Tg C yr-1




            250                                                                                          400
            200                                                                                          350
                                                   N Deposition Effects
            150                                                                                          300




                                                                                             Tg C yr-1
                                                   Total C Sequestration
            100                                                                                          250
             50                                                                                          200
              0                                                                                          150
                   USA                                                                                   100
                                                                                                          50
                                                                                                           0

                  USANdep: --
                                                                                                               Canada
                  USANdep: --

                                                                                       400
                                                                                       350
                                                                                       300

                                                                           Tg C yr-1
                                                                                       250
                                                                                       200
                                                                                       150
                                                                                       100
                                                                                        50
                                                                                         0
                                                                                                         Mexico
         Carbon Sequestration in
          North America (PgC)

                    N-         Other        All
                stimulated   Mechanisms

USA              +0.051       +0.259      +0.310
Canada           +0.023        -0.019     +0.004
Other            +0.010       +0.038      +0.048
North America    +0.084       +0.278      +0.362
               Conclusions

• We estimate that N-stimulate carbon
  sequestration accounts for about ¼ of the
  current C sink in North America.
• Other important mechanisms include land
  cover and land use changes and CO2
  fertilization.
• Biogeochemistry models used in carbon-cycle
  studies must include coupled C-N cycles.

								
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