A global model of changing N2O emissions from natural and perturbed soils |
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| Authors: | C D Nevison G Esser E A Holland |
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| Institution: | (1) National Center for Atmospheric Research, Boulder, Colorado, USA;(2) Institute for Plant Ecology, Justus-Liebig-University, Giessen, Germany |
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| Abstract: | A high resolution global model of the terrestrial biosphere is developed to estimate changes in nitrous oxide (N2O) emissions from 1860–1990. The model is driven by four anthropogenic perturbations, including land use change and nitrogen inputs from fertilizer, livestock manure, and atmospheric deposition of fossil fuel NO
x
. Global soil nitrogen mineralization, volatilization, and leaching fluxes are estimated by the model and converted to N2O emissions based on broad assumptions about their associated N2O yields. From 1860–1990, global N2O emissions associated with soil nitrogen mineralization are estimated to have decreased slightly from 5.9 to 5.7 Tg N/yr, due mainly to land clearing, while N2O emissions associated with volatilization and leaching of excess mineral nitrogen are estimated to have increased sharply from 0.45 to 3.3 Tg N/yr, due to all four anthropogenic perturbations. Taking into account the impact of each perturbation on soil nitrogen mineralization and on volatilization and leaching of excess mineral nitrogen, global 1990 N2O emissions of 1.4, 0.7, 0.4 and 0.08 Tg N/yr are attributed to fertilizer, livestock manure, land clearing and atmospheric deposition of fossil fuel NO
x
, respectively. Consideration of both the short and long-term fates of fertilizer nitrogen indicates that the N2O/fertilizer-N yield may be 2% or more.C. NBM Definitions
AET
mon
(cm H2O) = monthly actual evapotranspiration
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AET
ann
(cm H2O) = annual actual evapotranspiration
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age
h
(years) = stand age of herbaceous biomass
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age
w
(years) = stand age of woody biomass
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atmblc
(gC/m2/month) = net flux of CO2 from grid
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biotoc
(gC/g biomass) = 0.50 = convert g biomass to g C
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beff
h
= 0.8 = fraction of cleared herbaceous litter that is burned
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beff
w
= 0.4 = fraction of cleared woody litter that is burned
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bfmin
= 0.5 = fraction of burned N litter that is mineralized or converted to reactive gases which rapidly redeposit. Remainder assumed pyrodenitrified to N2. + N2O
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bprob
= probability that burned litter will be burned
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burn
h
(gC/m2/month) = herbaceous litter burned after land clearing
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burn
w
(gC/m2/month) = woody litter burned after land clearing
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cbiomsh
(gC/m2) = C herbaceous biomass pool
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cbiomsw
(gC/m2) = C woody biomass pool
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clear
(gC/m2/month) = woody litter C removed by land clearing
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clearn
(gN/m2/month) = woody litter N removed by land clearing
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cldh
(month–1) = herbaceous litter decomposition coefficient
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cldw
(month–1) = woody litter decomposition coefficient
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clittrh
(gC/m2) = C herbaceous litter pool
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clittrw
(gC/m2) = C woody litter pool
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clph
(month–1) = herbaceous litter production coefficient
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clpw
(month–1) = woody litter production coefficient
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cnrath
(gC/gN) = C/N ratio in herbaceous phytomass
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cnrats
(gC/gN) = C/N ratio in soil organic matter
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cnratt
(gC/gN) = average C/N ratio in total phytomass
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cnratw
(gC/gN) = C/N ratio in woody phytomass
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crod
(month–1) = forest clearing coefficient
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csocd
(month–1) = actual soil organic matter decompostion coefficient
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decmult
decomposition coefficient multiplier; natural =1.0; agricultural =1.0 (1.2 in sensitivity test)
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fertmin
(gN/m2/month) = inorganic fertilizer input
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fleach
fraction of excess inorganic N that is leached
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fligh
(g Lignin/ g C) = lignin fraction of herbaceous litter C
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fligw
(g Lignin/ g C) = 0.3 = lignin fraction of woody litter C
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fln2o
= .01–.02 = fraction of leached N emitted as N2O
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fnav
= 0.95 = fraction of mineral N available to plants
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fosdep
(gN/m2/month) = wet and dry atmospheric deposition of fossil fuel NO
x
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fresph
= 0.5 = fraction of herbaceous litter decomposition that goes to CO2 respiration
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fresps
= 0.51 + .068 * sand = fraction of soil organic matter decomposition that goes to CO2 respiration
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frespw
= 0.3 * (* see comments in Section 2.3 under decomposition) = fraction of woody litter decomposition that goes to CO2 respiration
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fsoil
= ratio of NPP measured on given FAO soil type to NPFmiami
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fstruct
= 0.15 + 0.018 * ligton = fraction of herbaceous litter going to structural/woody pool
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fvn2o
= .05–.10 = fraction of excess volatilized mineral N emitted as N2O
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fvol
= .02 = fraction of gross mineralization flux and excess mineral N volatilized
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fyield
ratio of total agricultural NPP in a given country in 1980 to total NPPmiami of all displaced natural grids in that country
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gimmob
h
(gN/m2/month) = gross immobilization of inorganic N into microbial biomass due to decomposition of herbaceous litter
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gimmob
s
(gN/m2/month) = gross immobilization of inorganic N into microbial biomass due to decomposition of soil organic matter
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gimmob
w
(gN/m2/month) = gross immobilization of inorganic N into microbial biomass due to decomposition of woody litter
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graze
(gC/m2/month) = C herbaceous biomass grazed by livestock
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grazen
(gN/m2/month) = N herbaceous biomass grazed by livestock
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growth
h
(gC/m2/month) = herbaceous litter incorporated into microbial biomass
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growth
w
(gC/m2/month) = woody litter incorporated into microbial biomass
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gromin
h
(gN/m2/month) = gross N mineralization due to decomposition and burning of herbaceous litter
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gromin
s
(gN/m2/month) = gross N mineralization due to decomposition of soil organic matter
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gromin
w
(gN/m2/month) = gross N mineralization due to decomposition and burning of woody litter
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herb
herbaceous fraction by weight of total biomass
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leach
(gN/m2/month) = leaching (& volatilization) losses of excess inorganic N
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ligton
(g lignin-C/gN) = lignin/N ratio in fresh herbaceous litter
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LP
h
(gC/m2/month)= C herbaceous litter production
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LP
(gC/m2/month) = C woody litter production
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LPN
h
(gN/m2/month) = N herbaceous litter production
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LPN
W
(gN/m2/month) = N woody litter production
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manco2
(gC/m2/month) = grazed C respired by livestock
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manlit
(gC/m2/month) = C manure input (feces + urine)
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n2oint
(gN/m2/month) = intercept of N2O flux vs gromin regression
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n2oleach
(gN/m2/month) = N2O flux associated with leaching and volatilization of excess inorganic N
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n2onat
(gN/m2/month) =  natural N2O flux from soils
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n2oslope
slope of N2O flux vs gromin regression
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nbiomsh
(gN/m2) = N herbaceous biomass pool
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nbiomsw
(gN/m2) = N woody biomass pool
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nfix
(gN/m2/month) = N2 fixation + natural atmospheric deposition
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nlittrh
(gN/m2) = N herbaceous litter pool
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nlittrw
(gN/m2) = N woody litter pool
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nmanlit
(gN/m2/month) = organic N manure input (feces)
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nmanmin
(gN/m2/month) = inorganic N manure input (urine)
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nmin
(gN/m2) = inorganic N pool
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NPP
acth
(gC/m2/month)= actual herbaceous net primary productivity
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NPP
actw
(gC/m2/month) = actual woody net primary productivity
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nvol
(gN/m2/month) = volatilization losses from inorganic N pool
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plntnav
(gN/m2/month)= mineral N available to plants
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plntup
h
(gN/m2/month) = inorganic N incorporated into herbaceous biomass
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plntup
w
(gN/m2/month) = inorganic N incorporated into woody biomass
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precip
ann
(mm) = mean annual precipitation
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precip
mon
(mm) = mean monthly precipitation
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pyroden
h
(gN/m2/month) = burned herbaceous litter N that is pyrodenitrified to N2
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pyroden
w
(gN/m2/month) = burned woody litter N that is pyrodenitrified to N2
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recyc
fraction of N that is retranslocated before senescence
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resp
h
(gC/m2/month) = herbaceous litter CO2 respiration
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resp
s
(gC/m2/month) = soil organic carbon CO2 respiration
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resp
w
(gC/m2/month) = woody litter CO2 respiration
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sand
sand fraction of soil
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satrat
ratio of maximum NPP to N-limited NPP
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soiloc
(gC/m2) = soil organic C pool
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soilon
(gN/m2) = soil organic N pool
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temp
ann
(°C) = mean annual temperature
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temp
mon
(°C) = mean monthly temperature
Now at the NOAA Aeronomy Laboratory, Boulder, Colorado. |
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