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

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

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)

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.

Loulergue et al. Nature, 2008

~350 ppb ≈ 975 Tg

Global Methane Budget 2003‐2012

http://www.globalcarbonatlas.org

Provided by: Michel, White CU INSTAAR; Dlugokencky NOAA ESRL

Geological Sources

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] 

Bartlett and Harriss 1993

32 – 80 Tg3 – 17 Tg34 – 65 Tg

80 – 115 Tg

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).

Hugelius et al. 2013; Schuur et al. 2015

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

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

Palsa (n=3)

Eriophorum (n=3)

Sphagnum (n=3)

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

Megonigal et al. 2004

Ben Woodcroft2017, in prep

Genome-centric analysis of whole community carbon metabolism

across the thaw gradient and by depth

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

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

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

Bubier et al. 2005

Hydrology affects CH4 flux from Wetlands

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

Bartlett and Harriss 1993

Temperature affects CH4 flux from Northern Wetlands

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

Sweeney et al. GRL 2016

Saunois et al. ESSD 2016

Thornton et al. GRL, 2016

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??

1. shallow lakes look like wetlands

wetlands definitions generally include most shallow Arctic lakes:

< 2 m depth, < 0.1 km2 = wetland

2. higher resolution surveys now resolve small lakes/ponds

3. small lakes don’t emit CH4 like wetlands

small lakes and ponds emit more CH4 per unit area

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

Thornton et al. GRL, 2016

Can δ13C-CH4 help us?

Fisher et al. Arctic Methane Sources. GRL, 2012

Atmospheric δ13C-CH4 above Laptev, East Siberian, Chukchi Seas (2014)

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

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 talkpatrick.crill@geo.su.se

And/or put you in contact with those members of the team who can best address your questions