U.S. Department of the Interior

U.S. Geological Survey

Soil CO2 and CH4 Emissions and

Carbon Budgeting in Dry Floodplain

Wetlands

Jackie Batson1, Gregory B. Noe1, Cliff R. Hupp1, Ken W.

Krauss2, Nancy B. Rybicki1, and Edward R. Schenk1

1National Research Program, Reston, VA, USA 2National Wetlands Research Center, Lafayette, LA, USA

River floodplains

Understand river-floodplain carbon cycling to:

assess the controls on greenhouse gas

emissions

determine the potential for floodplain carbon

sequestration.

Noe. 2012. Treatise of Geomorphology. Modified from NRC 2002.

Four dimensions of river corridors influence floodplain ecosystem processes

through river-floodplain hydrologic connectivity

This heterogeneity is critical to the prediction and scaling

of floodplain effects on carbon cycling

Goals of this study:

quantify carbon fluxes through soil CO2 and CH4

emissions

determine the controls on soil aerobic and anaerobic

respiration

develop an urban floodplain carbon budget along lateral

and longitudinal gradients of hydrologic connectivity

compare CO2 flux results using an infrared gas analyzer

and gas chromatograph

longitudinal

gradients

Difficult Run floodplain study

Difficult Run floodplain study

lateral

gradients

levee

backswamp

toe

slope

CO2 and CH4 (and N2O) flux

measurements

Soil CO2 fluxes

measured every three

weeks for one year on a

LI-COR 8100 infrared

gas analyzer (IRGA)

Gas samples extracted

quarterly from chamber

incubations and

analyzed for CO2, CH4,

and N2O on a gas

chromatograph

Mineralization

Hydroperiod

Litterfall

Sedimentation

Bank erosion

Other ecosystem process

measurements

CO2 flux: lateral and longitudinal

gradients

Site location

0 1 2 3 4 5

CO

2 f

lux

(g

C m

-2 y

-1)

400

600

800

1000

1200

1400

1600

1800

2000

2200Levee CO2

Backswamp CO2

Toeslope CO2

Longitudinal CO2 flux

(g C m-2 yr-1)

0 1316

1 1234

2 1491

3 1084

4 1587*

5 1076

Lateral CO2 flux

(g C m-2 yr-1)

Levee 1518

Backswamp 1115

Toeslope 1116

*no toe slope

Intra-annual CO2 flux controlled by

temperature

Factor p

Time <0.0001

Longitudinal position 0.0161

Lateral position 0.0003

Lateral*time 0.0002

Longitudinal*time <0.0001

Lateral*longitudinal 0.0155

Lateral*longitudinal*time <0.0001

Soil Temperature

0 5 10 15 20 25 30

CO

2 f

lux

( m

CO

2-C

m-2

s-1

)

0.01

0.1

1

10

100

Annual CO2 flux correlations

% silt

log

an

nu

al

CO

2 f

lux

% nitrification litterfall C:P

NH4 mineralization rate

log

an

nu

al

CO

2 f

lux

P mineralization rate TP

r=.454

p=.008

r=.416

p=.016

r=-.379

p=.029

r=.360

p=.040

r=-.353

p=.008

r=-.516

p=.002

Annual CO2 flux controlled by hydrology

Water-filled pore space

20 40 60 80 100

Ann

ua

l C

O2 f

lux (

g C

m-2

yr-

1)

100

1000

10000

R2=0.349

p<0.001

CH4 flux

Water-filled pore space

Red dots indicate fluxes that differ significantly (=0.1) from zero.

0 20 40 60 80 100 120

An

nu

al C

H4 f

lux

(g

C m

-2 y

-1)

-6

-4

-2

0

2

4

6

8

10

GC CO2 flux (mol m-2 s-1)

-1 0 1 2 3 4 5

IRG

A C

O2 f

lux

(

mo

l m

-2 s

-1)

-1

0

1

2

3

4

5

IRGA vs. GC

1:1

Method Mean SE

IRGA, 3.5 m 1.27 0.13

GC, 20 m 0.64 0.08

p<0.001

Method Mean SE

IRGA, 3.5 m 1.27 0.13

IRGA, 20 m 1.18 0.13

p=0.087

Method Mean SE

IRGA, 20 m 1.18 0.13

GC, 20 m .64 0.08

p<0.001

IRGA vs. GC

R² = 0.9911

R² = 0.9785

R² = 0.9979

R² = 0.996

R² = 0.9386

R² = 0.9867

300

400

500

600

700

800

900

1000

0 200 400 600 800 1000 1200 1400

CO

2 (

pp

m)

time (s)

Tamarack CO2

3A

3B

3C

3D

3E

3F

300

400

500

600

700

800

900

1000

0 200 400 600 800 1000 1200 1400

CO

2 (

pp

m)

time (s)

Tamarack 20 min IRGA CO2

3A

3B

3C

3D

3E

3F

350

400

450

500

550

0 50 100 150 200 250

CO

2 (

pp

m)

time (s)

Tamarack IRGA CO2

3A

3B

3C

3D

3E

3F

Difficult Run C budget g C m-2 y-1

Erosion Aerobic

respiration

Anaerobic

respiration

Deposition

Aboveground

production Allochthonous

sedimentation

Belowground

production

CO2 CH4

124

229

1223

Sequestration

or Loss

(-0.4)

-907

37

Oxidizing system

-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

De

c-1

0

Jan-1

1

Feb

-11

Ma

r-11

Apr-1

1

Ma

y-1

1

Jun-1

1

Jul-1

1

Aug-1

1

Sep-1

1

Oct-1

1

No

v-1

1

Wate

r le

vel (m

)

Site 5 well

Among all sites:

Average water level= -0.84 m

Average hydroperiod = 7.61% of

days with surface water present

Summary

C losses through respiration exceeded C

inputs

Annual aerobic respiration was largely

controlled by hydrology

CO2 fluxes were higher when measured with

an infrared gas analyzer versus samples

collected and analyzed on a GC

Thank you!