significant bomb d 14 c enrichment in deep soil: a previously unrecognized decadal c pool?
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Significant Bomb D 14 C Enrichment in Deep Soil: A Previously Unrecognized Decadal C Pool?. W. Troy Baisden and Roger L Parfitt Landcare Research, Palmerston North, New Zealand. Funded by NZ Foundation for Research Science and Technology Ministry of Agriculture and Forestry - PowerPoint PPT PresentationTRANSCRIPT
Significant Bomb 14C Enrichment in Deep Soil: A Previously Unrecognized Decadal C Pool?
W. Troy Baisden and Roger L Parfitt
Landcare Research, Palmerston North, New Zealand
Funded by NZ Foundation for Research Science and TechnologyMinistry of Agriculture and Forestry
US-NZ Climate Change Partnership through NZ Govt
-400 -200 0 200
0
50
100
150
Dep
th (
cm)
∆14C (‰, pre-bomb atm.= 0)
% Modern Carbon (1950 atmosphere)
80 100 12060
1952
1997
California Grassland Soil
Baisden et al 2002, Global Biogeochemical Cycles
Koputaroa, New ZealandGoh et al, 1976Syers et al, 1970
Judgeford, New ZealandO’Brien and Stout, 1978
Understanding Carbon Storage and Turnover•The balance between inputs and outputs
Soil Organic Matter
Inputs Outputs
The Model
DOM
vDOM
kDOM
Concentration
Model Formulation for DRDSC(Decadally Reactive Deep Soil C)
• Mass (g/m2)
• Downward Transport (cm/yr)
• First Order Loss Coefficient (yr-1)
• E-folding Depth (cm)
• No interactions with other 3 pools
• Is DRDSC from roots or dissolved organic matter (DOM)?– Progressive enrichment in most profiles– Below rooting zone
Data Assimilation via a Genetic Algorithm
• Evolves a chromosome of parameter values toward the best value for the model fit (based on an ‘objective function’)
• Inefficient but searches parameter space on both sides of the bomb-C spike
• Monte-Carlo style variation in 14C and %C data• Parameter uncertainty estimated from Monte-Carlo
– Greater of:• Standard deviation of best fits with data PDFs• Difference between best fit with and without PDFs included
• Emphasizing fitting DRDSC pool sizes
Koputaroa Soil, New Zealand
14C (per mil)
Cu
mla
tive
So
il M
ass
(g c
m-2)
Soil Organic Carbon (SOC) Pools Estimated by the ModelSite Max.
DepthIncluded
inAnalysis
(m)
Total SOC
(MgC/ha)
SOCwith turnover <100 yr
(MgC/ha)
DRDSC
(MgC/ha)
Koputaroa 0.8 148±4 81±4 10±3Judgeford 1.0 192±10 131±7 10.3±0.7*
TurlockLake
1.1 33±2 13±1 4.7±3.3
Riverbank 3.6 39±3 12±2 9.0±1.3*Model appears to underestimate DRDSC pool size.
Model-Estimated Soil Organic Carbon (SOC) PoolsSite Max.
DepthIncluded
inAnalysis
(m)
Ratio ofDRDSC toTotal SOC
Ratio ofDRDSC toSOC withturnover<100 yr
Koputaroa 0.8 0.07±0.02 0.13±0.04Judgeford 1.0 0.054±0.005* 0.078±0.008*
TurlockLake
1.1 0.14±0.10 0.37±0.27
Riverbank 3.6 0.23±0.05 0.74±0.05*Model appears to underestimate DRDSC pool size.
DRDSC as a Fraction of Total SOC
•10-20% of Deep Soil C has Decadal Dynamics
•Possibly increasing with Depth?
•Better understanding of DOC needed!
•10-20% of Deep Soil C has Decadal Dynamics
•Possibly increasing with Depth?
•Better understanding of DOC needed!
Koputaroa