Supplementary methods: C dynamics model (S1) Long-term CO2 ... · Supplementary methods: C dynamics...

Supplementary methods: C dynamics model (S1)

Long-term CO2 production following permafrost thawing

Bo Elberling1,2 Anders Michelsen3,1, Christina Schädel4, Edward A.G. Schuur4, Hanne H.

Christiansen2,5, Louise Berg1, Mikkel P. Tamstorf6 & Charlotte Sigsgaard1

Data assimilation was used to model decay rates and to optimise parameter (p) estimation. This inverse

modelling approach for incubation data is based on Bayes' theorem (suppl. equation 1), which states that the

posterior probability density function (PPDF) P(p|Z) of model parameters (p) can be obtained from prior

knowledge of parameters, represented by a prior probability density function P(p), and the information that is

contained in the incubation data set, represented by a likelihood function P(Z|p). See S1-S5.

)()|()|( pPpZPZpP (suppl. equation 1)

To perform the Bayesian inversion, we first specified the ranges (lower and upper limits, Supplementary

table 2) of model parameters according to literature values assuming a uniform distribution over the specific

parameter ranges. The likelihood function P(Z|p) (supplementary equation 2) was calculated on the

assumption that errors between observed and modelled values followed a Gaussian distribution where Z(t)

denotes the data obtained from measurements, X(t) is the modelled value and σ is the standard deviation of

the observed decomposition rate.

)(

22 )]()([

21exp)|(

iZobstii tXtZpZP

(suppl. equation 2)

Long-term CO2 production following permafrost thaw

SUPPLEMENTARY INFORMATIONDOI: 10.1038/NCLIMATE1955

NATURE CLIMATE CHANGE | www.nature.com/natureclimatechange 1

© 2013 Macmillan Publishers Limited. All rights reserved.

http://www.nature.com/doifinder/10.1038/nclimate1955

2

The probabilistic inversion approach constructs parameter distributions that allow inferences for parameter

uncertainties by quantifying maximum likelihood estimates (MLEs) for well-constrained parameters, means,

and confidence intervals (Supplementary table 2). Model validation was performed by parameter

visualisation, R2 statistics as well as graphical residual analysis.

As values for time zero for CO2 production in 1996 were not available, permafrost cores collected in 2008

from the exact same site and depths were incubated and the result used for the modelling.

References:

S1 Schädel C. et al. Separating soil CO2 efflux into C-pool-specific decay rates via inverse analysis of soil

incubation data. Oecologia 171, 721-732 (2013).

S2 Fang, C.; Smith, P. & Smith, J. U. Is resistant soil organic matter more sensitive to temperature than

the labile organic matter? Biogeosciences, 3, 65-68 (2006).

S3 Hastings, W. K. Monte-Carlo sampling methods using Markov chains and their applications.

Biometrika, 57, 97-109 (1970).

S4 Metropolis, N.; Rosenbluth, A. W.; Rosenbluth, M. N.; Teller, A. H. & Teller, E. Equation of state

calculations by fast computing machines. Journal of Chemical Physics, 21, 1087-1092 (1953).

S5 Xu, T.; White, L.; Hui, D. F. & Luo, Y. Q. Probabilistic inversion of a terrestrial ecosystem model:

analysis of uncertainty in parameter estimation and model prediction. Global Biogeochemical Cycles, 20,

GB2007, 15 PP. (2006)

2 NATURE CLIMATE CHANGE | www.nature.com/natureclimatechange

SUPPLEMENTARY INFORMATION DOI: 10.1038/NCLIMATE1955



Supplementary Tables:


Bo Elberling1,2 Anders Michelsen3,1, Christina Schädel4, Edward A.G. Schuur4, Hanne H.

Christiansen2,5, Louise Berg1, Mikkel P. Tamstorf6 & Charlotte Sigsgaard1

Suppl. Table 1: Site specific permafrost characteristics for the 5 sites, including the two soil types

in Zackenberg. Characteristics include depth to the permafrost measured as thickness of the active

layer (cm), carbon content in the top permafrost samples used for incubation (%C by weight) and

total carbon stock integrated to a depth of 1 m (kg m-2).

Site Name Country Location Active layer thickness

Permafrost C content

C stock in top 1 m

1 Baffin Island W Canada 73°02´N 84°32´W

45 (grassland) 3.1 24

2 Disko Island W Greenland 69°15’N 53°31’W


3A Zackenberg NE Greenland 74°30’N 20°30’W

75 (heath) 0.9 11

3B Zackenberg NE Greenland 74°30’N 20°30’W


4 Citronen Fj. N Greenland 83°12’N 28°04’W


5 Adventdalen Svalbard 78°12’N 15°50’E






2

Suppl. Table 2: Prior parameter ranges, maximum likelihood estimates (MLEs) and 95%

probability interval of parameters for each soil type. ki= pool-specific decay rate (day-1); fi = C pool

fractionation coefficient.

* for the poorly constrained parameter kpassive a mean value is calculated instead of a MLE

Parameter Lower Limit Upper Limit MLE 95% Probability Interval

Heath (dry)

ffast (x10-2) 0 5 1.16 (0.16, 4.22)

fslow (x10-1) 0 10 5.55 (4.54, 6.66)

kfast (x10-3) 0 20 2.7 (0.37,11.8)

kslow (x10-4) 0 30 6.97 (5.23, 9.15)

kpassive (x10-7)* 0 11 5.21 (0.76, 9.95)

Grassland (wet)

ffast (x10-2) 0 5 1.06 (0.12, 4.29)

fslow (x10-1) 0 10 1.12 (0.25, 2.63)

kfast(x10-3) 0 20 2.35 (0.35, 10.68)

kslow (x10-4) 0 30 4.29 (0.83, 14.39)

kpassive (x10-7)* 0 11 5.52 (0.8, 10.25)

Grassland (drained)

ffast (x10-2) 0 5 1.11 (0.14, 4.31)

fslow (x10-1) 0 10 7.49 (6.02, 9.02)

kfast (x10-3) 0 20 3.75 (0.53, 15.14)

kslow (x10-4) 0 30 8.55 (6.46, 11.27)

kpassive (x10-7)* 0 11 5.38 (0.75, 10.15)

Zackenberg

Supplementary figure S1: Location of the ZackenbergResearch Station in Northeast Greenland (Elberling et al. Long-term CO2 production following permafrost thawing).

Supplementary Figures:


Elberling et al.





Zackenberg

Supplementary figure S1: Location of the ZackenbergResearch Station in Northeast Greenland (Elberling et al. Long-term CO2 production following permafrost thawing).

Supplementary Figures:


Elberling et al.





Photo BE

Heath site

Supplementary figure S2: Zackenberg meteorological station and the ground moraine near the ZEROCALM 1 active layer thickness monitoring grid. The vegetation type is dominated by Cassiope tetragona (Elberling et al. Long-term CO2 production following permafrost thawing).





Supplementary figure S3: ZEROCALM 2 active layer monitoring grid in Zackenberg, illustrating the contrasting vegetation types from well-drained heath (Cassiope tetragona) to poorly drained wet grassland vegetation. The distinct vegetation zonation is controlled by the length of snow cover at this nivation site(Elberling et al. Long-term CO2 production following permafrost thawing).

Grassland site





= 0.8007x -1546.5 (R² = 0.61, p<0.05)

= 1.4701x -2873.9 (R² = 0.90, p<0.05)

0

20

40

60

80

100

1997 1999 2001 2003 2005 2007 2009 2011

Grassland

Heath

Supplementary figure S4: Maximum active layer thickness (±SD) between 1997-2012 measured at the end of August at the wet grassland and the well-drained heath sites at Zackenberg. The marked area indicate the depth interval (50-100 cm) used to assessing long changes in soil organic carbon stock associated with increasing maximum active layer thickness (Elberling et al. Long-term CO2 production following permafrost thawing).

Year

Dep

th (c

m)





0

40

80

120

160

200

0 2 4 6

Organic carbon (%) D

epth

(cm

)

0 10 20 30

C:N (by weight)

0 20 40 60 80 100

Water and ice (% by vol)

Grassland

Heath

Supplementary figure S5: Active layer and permafrost characteristics in Zackenberg (Site 3A,B) in August 2008. Horizontal lines indicate the mean active layer depth (end of August 1997-2008) at wet grassland (solid) and heath sites (dashed). Data from the active layer are based on samples collected from pits, while data from the permafrost are based on intact cores. Modified from Elberling et al. High nitrous oxide production from thawing permafrost. Nature Geosci. 3, 332-335 (2010).





Supplementary figure S6: Soil organic carbon (SOC) stocks based on repeated sampling in 1996, 2008 and 2012 at two contrasting soil types (n=3) in Zackenberg calculated for 0 - 1 m and for 0.5 - 1 m depth intervals. The latter depth interval (see supplementary figure 4S) is used to evaluate changes in SOC stock related to the increasing thickness of the active layer and corresponding permafrost thawing (Elberling et al. Long-term CO2 production following permafrost thawing).

0

5

10

15

20

25

30

35

1995 2000 2005 2010 2015

Heath 0-1 m

Heath 0.5-1 m

Grassland 0-1 m

Grassland 0.5-1 mSOC

sto

ck (k

g m

-2)





Supplementary figure S7: Longterm incubation of heath site top permafrost. A: basal soil respiration measured as CO2 being produced from intactcores (±SD), B: first 3 years of A and C: decreasing total dissolved C (DOC) and solid organic C (SOC).

Elberling et al. Long-term CO2 production following permafrost thawing.0

3

6

9

12

15

0 30 60 90 120 150

Time (months)

0.0

0.2

0.4

0.6

0.8

1.0

Heath

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0 30 60 90 120 150

Time (months)

First 3 years

y = 0.1092e-0.0267x

R2 = 0.988 , p<0.05)0.00

0.02

0.04

0.06

0.08

0.10

0.12

0 10 20 30 40

Time (months)

Bas

al s

oil r

espi

ratio

n( µ

g C

per

h p

er g

soi

l)

SO

C (%

)

DO

C (p

pm)

A B

C

First 3 years





Supplementary figure S8: Longterm incubation of wet grassland top permafrost. A: basal soilrespiration measured as CO2 being producedfrom intact cores (±SD) , B: first 3 years of A and C: decreasing total dissolved C (DOC) and solid organic C (SOC).


50

100

150

200

250

0 30 60 90 120 1502.6

2.8

3.0

3.2

3.4

Time (months)

SO

C (%

)

DO

C (p

pm)

C

0.00

0.01

0.02

0.03

0 30 60 90 120 150Time (months)

Bas

al s

oil r

espi

ratio

n( µ

g C

per

h p

er g

soi

l)

A

Wet grassland

y = 0.0298e‐0.025x

R2 = 0.9874, p<0.05)

0.00

0.01

0.02

0.03

0 10 20 30 40

First 3 years

Time (months)

B

First 3 years





Supplementary figure S9: Longterm incubation of wet grassland top permafrost (drained). A: basal soil respiration measured as CO2 being produced from intact cores (±SD), B: first 3 years of A and C: decreasing total dissolved C (DOC) and solid organic C (SOC).


50

100

150

200

250

0 30 60 90 120 1500.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

y = 0.5474e-0.027x

R2 = 0.9837, p<0.05)0.0

0.2

0.4

0.6

0 10 20 30 40

Wet grassland - drained

0.0

0.2

0.4

0.6

0 30 60 90 120 150

Time (months)

SO

C (

%)

DO

C (

ppm

)

C

SO

C (

%)

DO

C (

ppm

)

Time (months)

Bas

al s

oil r

espi

ratio

n(

µg C

per

h p

er g

soi

l) A First 3 years

Time (months)

B

First 3 years





0.6

1.0

0 2 4 6 8

Temperature (C)

10

2.0

0.8

Supplementary figure S10: Temperature-dependent CO2 production based on permafrost samples from Zackenberg measured three times during the long term incubation experiment (in 1997 shown as open squares, n=3; in 2003 shown as filled squares, n=1 and in 2008 (filled triangles, n=3). All data are normalized to 5 C and an exponential fit to 2003 data is shown as a dashed line (y = 0.6233e0.0903x, R2 = 0.9825, p< 0.05) indicating a Q10-value of 2.47 (Elberling et al. Long-term CO2 production following permafrost thawing).

Nor

mal

ized

bas

al s

oil r

espi

ratio

n(m

easu

red

as µ

g C

O2

per h

per

g s

oil)





Supplementary Figure S11: Potential C pool loss from top permafrost samples over a 50 year incubation period at 5°C for A) dry heath site B) wet grassland site and C) drained grassland site. The black lines depict mean potential C loss and the gray lines 95% confidence interval (Elberling et al. Long-term CO2production following permafrost thawing).

A: Heath (dry)

0

20

40

60

80

100

B: Grassland (wet)C lo

ss (%

initi

al C

)

0

20

40

60

80

100

C: Grassland (drained)

Incubation years0 10 20 30 40 50

0

20

40

60

80

100

Mean

95% Confidence Interval





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