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Wetland Sources and Their Contributions to Arctic Methane Emissions
Patrick CrillDept of Geological SciencesBolin Centre for Climate ResearchStockholm University
patrick.crill @geo.su.seStordalen Mire
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Methane Formationgeneralities
• Metabolic product of methanogenic Archaea
• The main substrates are acetate or CO2+H2:CH3COOH CH4 + CO2CO2 + 4H2 CH4 + 2H2O
(There are a few “non-competitive” subtrates (demethylation of osmotic regulators, e.g. glycine betaine, trimethylamine, DMSP))
• Formed at low Eh: < -200mV(very low O2, SO42- and NO3- concentrations)
Methanogenesis is strictly an ANAEROBIC process
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Methane oxidation
• Catalyzed by methanotrophic or methylotrophic bacteria and archaea
• The main substrates are CH4 and O2:CH4 + 2O2 CO2 + 2H2O
Methane oxidation is mostly an AEROBIC process
(marine sediments, metalliferous and hypersaline environments are the exceptions)
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Some Points about Tropospheric CH4
1. Its mixing ratio is increasing in troposphere, with a rate that appears to have become variable in recent years.
2. The reason for the increasing trend is not clearly established, but both natural and anthropogenic sources appear to be important.
3. Its mixing ratio is larger by 5 – 10% in NH compared to SH.
4. Its seasonality is similar to that of CO2.
5. Its principal removal mechanism from the troposphere is chemical decomposition by OH attack. Its lifetime is thought to be 8 to 11 years.
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Loulergue et al. Nature, 2008
~350 ppb ≈ 975 Tg
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Global Methane Budget 2003‐2012
http://www.globalcarbonatlas.org
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Provided by: Michel, White CU INSTAAR; Dlugokencky NOAA ESRL
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Geological Sources
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Global Vegetation C 650 PgGlobal Soil C (1m) 1500 PgAtmosphere 777+ Pg
Permafrost Zone Soil CPeatlands (several m) 277 PgMineral Soil (3m) 747 PgSiberian Deep C (~25m) 407 PgAlluvial Deep C (~25m) 241 Pg
1672 Pg
Global Carbon Pools
[Jobaggy 2000, Field et al. 2007, Zimov et al. 2006, Tarnocai et al. 2009, Schuur et al. 2008]
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Bartlett and Harriss 1993
32 – 80 Tg3 – 17 Tg34 – 65 Tg
80 – 115 Tg
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McGuire et al. 2010
Terrestrial areas of the Arctic were a net source of 41.5 Tg CH4 yr−1 that increased by 0.6 Tg CH4 yr−1during the decade of analysis (1997‐2006).
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Hugelius et al. 2013; Schuur et al. 2015
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Euskirchen etal. 2007 in Hinzman et al. Ecol Appl 2013
1970-2000
Timing of snowmelt
Shifting Trends in the Arctic
1910-1940
Timing of snow return
Surface energy flux due to snow cover
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CH4 + 2O2 → CO2 + 2H2O
CH3COOH → CH4 + CO2CO2 + 4H2 → CH4 + 2H2O
Drained or Dry Peatlands and PermafrostPalsa, Heath
Drains to Local HydrologyWoody Plants and Shrubs
Wet Peat or Corg AccumulatingBogs, Sediments
OmbrotrophicPerched above Regional Hydrology
Lower Rates of Production
Very Wet Productive SystemsFens, Swamps, Littoral
MinerotrophicLinked to Regional HydrologySignificant Annual Production
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Palsa (n=3)
Eriophorum (n=3)
Sphagnum (n=3)
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Day of Year0 100 200 300
mo
l CO
2 m
-2s-
1
-4
-3
-2
-1
0
1
Stordalen Mire, 2012-16
0 100 200 300
mg
CH
4 m
-2d
-1
0
50
100
150
200
250
300
FenBogPalsa
PARavg
100 200 300 400 500
mol
CO
2 m
-2 s
-1
-4
-3
-2
-1
0
1
Jan - MarApr - JunJul - SepSep - Dec
MethaneAccum Fen Fluxes g m-2
EC AC
Winter 4.23 4.27Spring 2.14 1.13Growing 20.67 21.48
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Megonigal et al. 2004
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Ben Woodcroft2017, in prep
Genome-centric analysis of whole community carbon metabolism
across the thaw gradient and by depth
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Mean 13C = -65‰
Mean:13C = -79‰
… and archaeal communities from CO2 reductive towards acetoclastic clades
bacteria
‐50
‐60
‐70
‐80
‐90
‐100
13 C o
f CH
4flu
x
0 20 40 60 80 1000 10 20 30 40 5060Frequency
P E RMA F RO S T T H AW
Thaw shifts methane isotopically heavier…
Concordant responses of
isotope geochemistry
and microbial
communities
Spaghnum(thawing)
Eriophorum(thawed)
more
CO2redu
ction
more
Acetate
Ferm
entatio
n
McCalley et al., (2014) Nature
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Simulated daily CH4 production partitioned into hydrogenotrophic & acetotrophic production
2011
2012
2013
Sphagnum Eriophorum
6/1/2011 7/1/2011 8/1/2011 9/1/2011 10/1/2011 11/1/20110.0
0.2
0.4
0.6
0.8
1.0
60
0
0
0
0
6/1/2012 7/1/2012 8/1/2012 9/1/2012 10/1/2012 11/1/20120.0
0.2
0.4
0.6
0.8
1.0
60
0
0
0
0
6/1/2013 7/1/2013 8/1/2013 9/1/2013 10/1/2013 11/1/20130.0
0.2
0.4
0.6
0.8
1.0
60
0
0
0
0
Frac
tion
of H
M
0.0
0.5
1.0
1.5
2.0
a
b
0.0
0.5
1.0
1.5
2.0
Frac
tion
of H
M
c
Frac
tion
of H
M
0.0
0.5
1.0
1.5
2.0
Date (month/day/year)
16/1/2011 7/1/2011 8/1/2011 9/1/2011 10/1/2011 11/1/20110.0
0.2
0.4
0.6
0.8
1.0
26/1/2012 7/1/2012 8/1/2012 9/1/2012 10/1/2012 11/1/20120.0
0.2
0.4
0.6
0.8
1.0
36/1/2013 7/1/2013 8/1/2013 9/1/2013 10/1/2013 11/1/20130.0
0.2
0.4
0.6
0.8
1.0
d
0
2
4
6
CH
4 pro
duct
ion
(kg
C h
a-1 d
ay-1
)
e
CH
4 pro
duct
ion
(kg
C h
a-1 d
ay-1
)
0
1
2
3
4
5
6
f
0
1
2
3
4
5
6
Date (month/day/year)
CH
4 pro
duct
ion
(kg
C h
a-1 d
ay-1
)
hydrogenotrophic
acetotrophic
total
hydrogenotrophicfraction
Deng et al. JAMES, 2017
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6/1/2011 7/1/2011 8/1/2011 9/1/2011 10/1/2011 11/1/2011-90
-80
-70
-60
-50
-40
6/1/2012 7/1/2012 8/1/2012 9/1/2012 10/1/2012 11/1/2012-90
-80
-70
-60
-50
-40
6/1/2013 7/1/2013 8/1/2013 9/1/2013 10/1/2013 11/1/2013-90
-80
-70
-60
-50
-40
Eriophrum: Modeled Measured Sphagnum: Modeled Measured
d13 C
-CH
4 (0 / 0
0)
Date (month/day/year)
2011
2012
2013
Simulated and observed δ13C of daily CH4 fluxes
Deng et al. JAMES, 2017
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Bubier et al. 2005
Hydrology affects CH4 flux from Wetlands
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Water Table Depth, cm-50 -40 -30 -20 -10 0 10
mg
CH
4 m
-2 d
-1
0
200
400
600
800
1000
1200
1400
Wz vs Javg
Change from Previous Day's Water Table Depth, cm-3 -2 -1 0 1 2
mg
CH
4 m
-2 d
-1
0
200
400
600
800
1000
1200
1400
daily average fluxJune - October
Though not always in the way you expect
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Bartlett and Harriss 1993
Temperature affects CH4 flux from Northern Wetlands
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Stordalen Mire Fen
Tair
-15 -10 -5 0 5 10 15 20
mg
CH
4 m
-2d
-1
0
50
100
150
200
250
300
Jan - MarApr - JunJul - SepSep - Dec
1234 5 67 89
1011121314
15 1617 18 19
2021
222324
25 26
27
28
29
30
31
3233
34 3536
37
38
39
4041
42
4344454647
48 49505152
1
Though not always in the way you expect
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Sweeney et al. GRL 2016
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Saunois et al. ESSD 2016
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Thornton et al. GRL, 2016
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High Latitude CH4 Emissions
inverse models (top-down):23 Tg yr-1
measurement-based (bottom-up):59.7 Tg yr-1
Are some sources double-counted in bottom-up accounting,
or are top-down inverse models wrong,or we don’t understand the sinks??
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1. shallow lakes look like wetlands
wetlands definitions generally include most shallow Arctic lakes:
< 2 m depth, < 0.1 km2 = wetland
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2. higher resolution surveys now resolve small lakes/ponds
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3. small lakes don’t emit CH4 like wetlands
small lakes and ponds emit more CH4 per unit area
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Thornton et al. GRL, 2016
4. Pixilation loses area of open water
Stordalen Mire, Sweden
49% loss of estimated openwater area when decreasing from2 m to 350 m pixel resolution
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Thornton et al. GRL, 2016
Can δ13C-CH4 help us?
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Fisher et al. Arctic Methane Sources. GRL, 2012
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Atmospheric δ13C-CH4 above Laptev, East Siberian, Chukchi Seas (2014)
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Some Challenges
• Driving Data Sets are Poor in High Latitude Regions
• Need more data for isotopologues for source apportionment in mixing models δD-CH4
• Representation of Hydrology/Methane Dynamics
• Effects of Permafrost Dynamics on Hydrology
• Representation of Lakes/Ponds, Disturbance andBiological Community Change
• Report model output in consistent latitude ranges: >50°N, >60°N, above Arctic Circle
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photo by Tyler Logan
Thanks to the Stockholm UniversityTrace Gas Biogeochemistry Lab:
Brett ThortonMartin Wik
Joachim JansenKristian Andersson
Abisko Scientific Research StationAbisko summer field crews
I/B Oden crewThe IsoGenie Team
I will be happy to answer questions about this [email protected]
And/or put you in contact with those members of the team who can best address your questions