biogeochemical processes of methane emission and uptake edward hornibrook bristol biogeochemistry...
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![Page 1: Biogeochemical processes of methane emission and uptake Edward Hornibrook Bristol Biogeochemistry Research Centre Department of Earth Sciences University](https://reader035.vdocuments.mx/reader035/viewer/2022070306/5515de34550346cf6f8b4bc8/html5/thumbnails/1.jpg)
Biogeochemical processes of methaneemission and uptake
Edward HornibrookBristol Biogeochemistry Research Centre
Department of Earth SciencesUniversity of Bristol
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Outline
1. Methanogenesis & methanotrophy
2. Anaerobic C mineralisation in wetlands - uncertainties?
3. Stable isotopes & methane
4. Current BBRC research
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Alessandro Volta (1776) "Combustible Air"
Wolfe (1993)
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Universal Phylogenetic Tree of Life (16S & 18S RNA)Universal Phylogenetic Tree of Life (16S & 18S RNA)
Madigan et al (2003)
methanogens
methanotrophs
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C6H12O6 + 6 O2 6 CO2 + 6 H2O
G0 = -2870 kJ/mol
C6H12O6 3 CO2 + 3 CH4
G0 = -418 kJ/mol
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Methanogenic SubstratesMethanogenic Substrates
I. CO2-type substrates • Carbon dioxide, CO2
• Formate, HCOO-
• Carbon monoxide, COII. Methyl substrates • Methanol, CH3OH • Methylamine, CH3NH3
+
• Dimethylamine, (CH3)2NH2+
• Trimethylamine, (CH3)3NH+
• Methylmercaptan, CH3SH • Dimethylsulphide, (CH3)2S
III. Acetotrophic substrates • Acetate, CH3COO-
• Pyruvate, CH3COCOO-
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Diversity of methanogenic ArchaeaDiversity of methanogenic Archaea
Methanobacteriales5 Genera & 25 species; Substrates: mainly H2 + CO2, formate; Methanosphaera + methanol, Methanothermus + reduction of S0
Methanococcales5 Genera & 9 species; Substrates: mainly H2 + CO2, formate; Methanococcus + pyruvate
Methanomicrobiales8 Genera & 22 species; Substrates: mainly H2 + CO2, formate; Methanocorpusculum, Methanoculleus & Methanolacinia + alcohols
Methanosarcinales7 Genera & 19 species; Substrates: mainly methanol & methylamines;Methanosarcina & Methanosaeta + acetate; Methanohalophilus + methylsulphides; Methanosalsum + dimethylsulphide
Methanopyrales1 Genera & 1 species: Methanopyrus; hyperthermophile (110°C) Substrates: H2 + CO2
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Anaerobic Chain of DecayAnaerobic Chain of Decay
complex organics(cellulose, hemicellulose)
complex organics(cellulose, hemicellulose)
fermentive bacteriafermentive bacteria H2 + CO2 + HCOO-H2 + CO2 + HCOO-CH3CH2COO-
CH3CH2CH2COO-
CH3CH2COO-
CH3CH2CH2COO-
CH3COO-CH3COO-acetogenic bacteriaacetogenic bacteria
H2 + CO2H2 + CO2
methanogenic Archaeamethanogenic Archaea
homoacetogenic bacteriahomoacetogenic bacteria
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G0'
kJ/reaction
G0' standard conditions: solutes 1 M; gases 1 atm
The importance of syntrophyThe importance of syntrophy
C6H12O6 + 4 H2O 2 CH3COO- + 2 HCO3- + 4 H+ + 4 H2
C6H12O6 + 2 H2O CH3(CH2)2COO- + 2 HCO3- + 3 H+ + 2 H2
CH3(CH2)2COO- + 2 H2O 2 CH3COO- + H+ + 2 H2
CH3CH2COO- + 3 H2O CH3COO- + HCO3- + H+ + H2
2 CH3CH2OH + 2 H2O 2 CH3COO- + 2 H+ + 4 H2
C6H5COO- + 6 H2O 3 CH3COO- + CO2 + 2 H+ + 3 H2
4 H2 + HCO3- + H+ CH4 + 3 H2O
2 CH3COO- + H2O CH4 + HCO3-
4 H2 + 2 HCO3- + H+ CH3COO- + 4 H2O
-207
-135
+48
+76
+19
+47
-136
-31
-105
G-319
-284
-18
-6
-37
-18
-3
-25
-7
G typical in situ abundance of reactants & products: VFAs 1 mM; HCO3
- 5 mM; glucose 10 M; CH4 0.6 atm; H2 10-4 atm
Madigan et al (2003)
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Methanotrophic BacteriaMethanotrophic Bacteria
1. Aerobic methane oxidation (Proteobacteria)• Low affinity methanotrophs (culturable)• High affinity methanotrophs (no isolates to date)
2. Anaerobic methane oxidation• Marine environments• Methanogen/ sulphate-reducer consortia
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Substrates used by methylotrophs & methanotrophsSubstrates used by methylotrophs & methanotrophs
• Methane, CH4
• Methanol, CH3OH• Methylamine, CH3NH3
+
• Dimethylamine, (CH3)2NH2+
• Trimethylamine, (CH3)3NH+
• Tetramethylammonium, (CH3)4N+
• Trimethylamine N-oxide, (CH3)3NO• Trimethylsulphonium, (CH3)3S+
• Formate, HCOO-
• Formamide, HCONH2
• Carbon monoxide, CO• Dimethyl ether, (CH3)2O• Dimethyl ether, (CH3)2O• Dimethyl carbonate, CH3OCOOCH3
• Dimethyl sulphoxide, (CH3)2SO• Dimethylsulphide, (CH3)2S
methane mono-
oxygenase
CH4 ===> CH3OH
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Methanotrophic BacteriaMethanotrophic Bacteria
Type I (Ribulose monophosphate C-assimilation pathway) Methylomonas, Methylomicrobium, Methylobacter, Methylococcus
Type II (Serine C-assimilation pathway) Methylosinus, Methylocystis, Methylocella*, Methylocapsa*
*acidophiles isolated from peat bogs (Dedysh et al. 2000; 2002)
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Anaerobic C Mineralisation in WetlandsAnaerobic C Mineralisation in Wetlands
Tenet 1: Methanogenesis is the terminal step in anaerobic decay of
organic matter in freshwater wetlands.
Tenet 2: In most freshwater systems, 2/3 of methanogenesis occurs via acetate fermentation and 1/3 by CO2 reduction (H2).
Vile et al. (2003). Global Biogeochem. Cycles 17(2), 1058.• anaerobic C mineralisation in freshwater wetlands along a natural sulphate gradient• 36 to 27% SO4
2- reduction vs. <<1% methanogenesis• ? fermentation of organic acids CO2
Bridgham et al. (1998). Ecology 79, 1545-1561.
• anaerobic C mineralization via methanogenesis: 0.5% in bogs and <2% in fens
Wieder & Lang (1988). Biogeochemistry 5, 221-242. • anaerobic C mineralisation in West Virginian Sphagnum bog• 38 to 64% SO4
2- reduction vs. 2.8 to 11.7% methanogenesis
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Decoupling of Terminal Carbon Mineralisation PathwayDecoupling of Terminal Carbon Mineralisation Pathway
Hines et al. (2001). Geophys. Res. Lett. 28(22), 4251-4254.• northern wetlands: CH4 derived mainly from CO2/H2
• Acetate accumulation to high levels; ultimately degraded aerobically to CO2
• ?contribution to high levels of DOC/ organic acids in ombrotrophic bogs
Lansdown et al. (1992). Geochim. Cosmochim. Acta 56(9), 3493-3503.• Kings Lake Bog, Washington State (ombrotrophic peatland)• CH4 derived mainly from CO2/H2; confirmed with 14C tracer experiments
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winter earlyspring
spring-summer
Avery et al. (1999)
Nov Jan Feb Apr Jun Jul
Nov Jan Feb Apr Jun Jul
-45
-50
-55
-60
-65
13C
-CH
4 (
‰)
soil
(pea
t)te
mpe
ratu
re (
°C)
20151050
Buck Hollow Bog (Michigan, USA)Buck Hollow Bog (Michigan, USA)
0
200
400
600
800
acet
ate
(M
)
CR CR AF
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Duddleston et al. (2002). Geophys. Res. Lett. 28(22), 4251-4254.
1999
Ace
tate
(M
)
1000
800
600
400
200
100
25
0
5
0
-5
-10
-15
-20
-25
Dep
th (
cm)
Turnagain Bog (ombrotrophic peatland, Anchorage Alaska; pH 4.6 to 5.1)Turnagain Bog (ombrotrophic peatland, Anchorage Alaska; pH 4.6 to 5.1)
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'Underachieving' northern wetlands?'Underachieving' northern wetlands?
SO42-
H2S
O2
VFAs
CO2
acetate CH4
H2/CO2 CH4
• What is the mechanism of acetate production?
(i) heterotrophic or (ii) autotrophic
• Possible causes?: (i) temperature (ii) pH (iii) vegetation (iv) trophic level
Questions• How much C in acetate normally destined for CH4
is being converted to CO2?• How stable is the decoupling?
• CH4 flux & VFAs? (Christensen et al. 2003)
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-values-values
0 +
D, 13C, 15N, 18O, 34S (‰)
-
InternationalStandard
D, 13C, 15N, 18O or 34Sdepleted w.r.t. standard
D, 13C, 15N, 18O or 34Senriched w.r.t. standard
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VPDBVPDB
-90 -80 -70 -60 -50 -40 -30 -20 -10 0 +10
13C (‰)
atmospheric CH4
biological & abiological CH4
C4 plants
freshwater carbonates
marine carbonates
atmospheric CO2
C3 plants
petroleum & coal
eukaryotic algae
Stable Carbon IsotopesStable Carbon Isotopes
after Hoefs (1997)
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0 5 10 15 20 25Methane Flux (% of total)
Natural Wetlands
Landfills
FreshwaterGas Hydrates
Oceans
~ -70±5‰~ -60‰
~ -60‰
Ruminants
Rice PaddiesTermites
~ -63±5‰
~ -50±2‰~ -60±5‰
~ -66±5‰
Tyler et al. (1988), Wahlen (1994), Quay et al. (1991, 1999), Breas et al (2002)
13C of CH4 Sources13C of CH4 Sources
Biomass BurningCoal MiningNatural Gas
~ -24±3‰~ -36±7‰
~ -43±7‰
-60±5‰-40 to -86‰-40 to -86‰
13Cwt. avg. ~ -54.4‰13Catmosphere ~ -47.3‰
13Cwt. avg. ~ -54.4‰13Catmosphere ~ -47.3‰
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-50
-40
-30
-20
-10
0
10
20
-120 -110 -100 -90 -80 -70 -60 -50 -40 -30
13C-CH4 (‰)
13C
-C
O2 (
‰)
marine(CO2 reduction)
Whiticar M. J., Faber E., and Schoell M. (1986) Biogenic methane formation in marine and freshwater environments: CO2 reduction vs. acetate fermentation - Isotope evidence. Geochimica
et Cosmochimica Acta 50, 693-709.
freshwater(acetate fermentation)
methanotrophyor thermogenesis
C = 1.055
C ~ 54‰
C = 1.040
C ~ 40‰ C
~ 86‰
C = 1.090
CO -CH =CO + 1000
CH + 10002
42 4
CO -CH = CO - CH 2 4 2 4
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EnvironmentCO2-reduction
13C-CH4
13C of CH4 with pathway confirmed with 14C tracers13C of CH4 with pathway confirmed with 14C tracers
acetate13C-CH4
Study
coastal marine
peatland
rice paddy
coastal marine
freshwaterestuary
peatland (May)
peatland (June)
Alperin et al. (1992)
Lansdown et al. (1992)
Sugimoto & Wada (1993)
Blair et al. (1993)
Avery (1996)
Avery et al. (1999)
Avery et al. (1999)
-62 ‰
-73 ± 4 ‰
-77 to -60 ‰
-62 to -58 ‰
-72 ± 2.2 ‰
-72 ± 1.3 ‰
-71 ± 1.3 ‰
-39 to -37 ‰
n/a
-43 to -30 ‰
n/a
-43 ± 10 ‰
-43.8 ± 12 ‰
-44.5 ± 5.4 ‰
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-10
-20
20
10
0
-30-30-40-50-60-70-80-90
13 13
2 4088 58 4C CCO CHΣ = − −. . (r2 = 0.64; n = 55)Sifton Bog:
Hornibrook et al. (2000)
C = 86‰
13C-CH4 (‰)
13 C
-C
O2
(‰
)
C = 54‰
C = 40‰
AFCR
= -21.3‰ 13
2CCO
13
4CCH = -42.3‰
Point Pelee Marsh: (r2 = 0.83; n = 29)
€
13CΣCO2= −0.45δ13CCH4
− 40.1
180 cm
surface
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intersection: -42.3‰ (CH4) -21.3‰ (CO2)
Sugimoto & Wada (1993)
C3 compost (soybean meal & rice straw): 13C = -26.5‰C3 compost (soybean meal & rice straw): 13C = -26.5‰
dried rice plants: -39.7‰ -24.4‰
13C (CH3-)13C (COOH)
dried rice plants: 13C (CH3COOH) = -32.1‰dried rice plants: 13C (CH3COOH) = -32.1‰
kudzu (fresh green leaves): 13C (CH3COOH) = -32.9‰kudzu (fresh green leaves): 13C (CH3COOH) = -32.9‰
kudzu: -42.9‰ -22.9‰
CH3 - C - O-
=
O
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-10
-20
20
10
0
-30
-30-40-50-60-70-80-90
13C-CH4 (‰)
13 C
-C
O2
(‰
)
-40
Other WetlandsOther Wetlands
AFCRBog 3850
Bog S4
13
4CCH = -40.7 ± 6.1‰
= -23.9 ± 4.8‰ 13
2CCO
Sugimoto & Wada (1993)
Hornibrook et al. (2000)
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-10
-20
20
10
0
-30
-30-40-50-60-70-80-90
13C-CH4 (‰)
13 C
-C
O2
(‰
)
-40
Other WetlandsOther Wetlands
AFCR
12 cm
100 cm
Aravena et al. (1993), Lansdown et al. (1992), Waldron et al. (1999)
Kings Lake Bog (WA, USA)
0 cm
500 cm
Ellergower Moss (Scotland)
65 cm
170 cm
Rainy River Peatland (N. Ont.)
C = 86‰
C = 54‰
C = 40‰
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-10
-20
20
10
0
-30-40-50-60-70-80-90
13C-CH4 (‰)
13 C
-C
O2
(‰
)
shallow
deep
CH4 emissionsfrom wetlands
CH4 emissionsfrom wetlands
CO2 reduction
acetate fermentation
-60±5‰flux ? flux ?
shallow
Hornibrook et al. (2000)
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UK SitesUK Sites
• determine CH4 pathway predominance using 14C tracers• determine CH4 pathway predominance using 14C tracers
• determine the prevalence of these 13C distributions in different classes of natural wetlands (SW England & Wales)
• determine the prevalence of these 13C distributions in different classes of natural wetlands (SW England & Wales)
• determine relationship between pore water distribution and 13C signature of CH4 emissions
• determine relationship between pore water distribution and 13C signature of CH4 emissions
• Ms. Helen Bowes (NERC Ph.D. student)• Ms. Helen Bowes (NERC Ph.D. student)
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Field sitesField sites
1.Cors Caron2.Tor Royal, Dartmoor3.Llyn Mire4.Blanket bog, Elan Valley5.Gors Lywd, Elan Valley6.Crymlyn Bog7.Wicken Fen
1.Cors Caron2.Tor Royal, Dartmoor3.Llyn Mire4.Blanket bog, Elan Valley5.Gors Lywd, Elan Valley6.Crymlyn Bog7.Wicken Fen
1
2
4
6
7
3
5
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Summary
• The relative proportions of anaerobic processes in freshwater wetlands needs to be better characterised.
• How wide spread is decoupling of terminal stages of anaerobic C mineralisation in northern wetlands?
Models
• Better understanding of anaerobic C flow needed to represent microbial activity accurately in process-based models
• Integrated models of gas abundance/ emission + accurate simulation of stable isotope signatures.
• What controls decoupling? Can systems switch TCM processes?
• Can stable isotope signatures of CH4 be used as an accurate proxy for biogeochemical and physical processes?