Using 14C to investigate methane production and DOC reactivity in northern peatlands

Liz Corbett*, Jeffrey P. Chanton, Paul A. Glaser, William T. Cooper, Donald I. Siegel, Mimi Sarkar, Julianna D’AndrilliDepartment of Oceanography, Florida State University, Tallahassee, FL 32306

*corresponding author: corbett@ocean.fsu.edu

IntroductionPeatlands are a large carbon reservoirs. These ecosystems are saturated with water, and therefore, have an extremely low rate of decomposition. In this way, they have stored and accumulated carbon for over 6,000 years. With the current threat of global warming, they have the potential to become a carbon source to the outside environment by either leaching large amounts of DOC into connecting rivers or by producing CO2 and CH4 into the atmosphere by increased microbial respiration.

Purpose of StudyUnderstand why microbes in a fen environment show a

shift from acetate fermentation to CO2 reduction at depth,

but microbes in a bog environment utilize CO2 reduction

at all depthsQuantify the DOC size reservoirs in the peatland

environmentDifferentiate between bog and fen DOC Differentiate between deep and surface DOCDetermine which DOC sizes serve as a microbial food

sourceCategorize DOC based on size, aromaticity and structure EEMS plots showing UV

degradation as DOC travels downstream

Concentrations of DOC Separated by Size in Surface Fen and Bog

-20

0

20

40

60

80

100

0-1 1--3 3--10 10--100 100+

DOC Size Categories (kDa)

Per

cent

age

for

DO

C T

otal

RL2 Bog sfc

Crest Bog 0.5m

RL2 Fen 20cm

SR Fen 0.5m

Concentrations of DOC Separated by Size in Deep Fen and Bog

-20

0

20

40

60

80

100

0-1 1--3 3--10 10--100 100+

DOC Size Categories (kDa)

Perc

enta

ge o

f Tot

al D

OC

RL2 Bog 3m

Crest Bog 3m

RL2 Fen 2.5m

SR 3m

Size Filtration study showing larger concentrations of LMW DOC suggesting bacterial preferentially choose HMW DOC as a resource and leave behind LMW DOC to accumulate

Microbes seem to prefer fen DOC to bog DOC since the 14C value of their respiration products (CO2 and CH4) exactly matches DOC in the fen environments, but only partly matches bog DOC.

0

0.5

1

1.5

2

2.5

3

-400 -200 0 200

14C ‰

Dept

h (m

)

Peat

DOCDIC & CH4

BOG

0

0.5

1

1.5

2

2.5

3

-400 -200 0 200

14C ‰

Dept

h (m

)

Peat

DOC, DIC & CH4

FEN

2007 Bog and Fen C:N Ratio (corrected for ammonium and NOx)

0

1

2

3

4

5

-600.0 -400.0 -200.0 0.0 200.0 400.0 600.0

C:N

Dept

h (m

)

Lawn

LRB

RL2 Bog

RL2 Fen

WWT

Fen DOC has a lower C:N ratio meaning it is more labile and a better food source for the bacterial community

2008 Bog and Fen C:N Comparision (corrected for ammonium and NOx)

0

1

2

3

4

5

-600 -400 -200 0 200 400 600

C:N

Dep

th (m

)

RLIV Bog

SR Bog

RidgeBogFBc

RL4 Fen

SR Fen

ConclusionsData suggests that the structure or quality of DOC may differ

between the bog and fen environmentsFen DOC is more labile than bog DOC suggesting it as a better

food source for bacteriaThe concentration of LMW DOC increases with depth

suggesting LMW accumulates because it is not utilized by

bacteria, whereas HMW concentrations increase as the bacteria

metabolize it as a food sourceDOC degradation by UV light suggests that the DOC is made

up of aromatic groupsThe cross-plot shows a shift in metabolic pathways in the fen but

not in the bog

Cross-plot shows the transition from aceticlastic methanogenesis to CO2 reduction that the bacteria make in the fen with depth, but the constant use of the CO2 reduction at all depths occurs in the bogs