Using a Network of Flux Towers to Investigate the Effects of Wetland Restoration on Greenhouse Gas Fluxes

Dennis Baldocchi, Jaclyn Hatala, Joe Verfaillie, Sara Knox, Frank Anderson

Department of Environmental Science, Policy and ManagementUniversity of California, Berkeley

AGU, 2012

Delta Peatland is Subsiding!Landscape is Vulnerable to Flooding by Levee Failure;

Its Collapse would Shut-Down California’s Water Conveyance System

The Delta is a Vulnerable Ecosystem via Severe Land Subsidence

New Plans to Reverse Subsidence with Carbon Farming:Restored Tule Wetlands and Rice on

Twitchell and Sherman Islands

What are the: Cost/Benefits?; Unintended Consequences?

NEP (gC m-2 y-1)

-400 -200 0 200 400 600 800 1000 1200 1400

FC

H4

(gC

m-2

y-1

)

-40

-20

0

20

40

60

80

100

120

140

160

Coefficients:b[0]10.74b[1]0.068r ²0.7318

• Wetlands in California Provide Huge Potential to Sequester Carbon• Long Growing Season & Ample Sunlight Promotes Photosynthesis

• Flooding Retards Respiration

• At What Cost?• Annual Methane Emission Scales with Net Primary Productivity of

Wetlands, Natural and Managed

CH4

Anoxic Sediments

Water

Fluxes, Sources andSinks of Methane

Air-WaterExchange

Air, O2

Ebullition

AnaerobicMethanogenicArchaea

XylemTransport

Oxidation:MethanotropicBacteria

CO2

Anoxic Sediments

Water

Fluxes, Sources andSinks of Methane

Air-WaterExchange

Ebullition

AnaerobicMethanogenicArchaea

XylemTransport

Oxidation:MethanotropicBacteria

CO2

Over-Arching Research Questions

• How Does Management for Carbon Sequestration and Ecological Restoration affect Methane and Water Loss?– How Large are Carbon Dioxide and Methane Fluxes from

Drained & Managed Peatlands (Rice, Corn, Pasture) vs Restored Wetlands on daily, seasonal, annual time scales?

– How do Greenhouse Gas Fluxes Respond with Environmental Drivers (Light, Temperature, Oxygen, recent Photosynthesis, Water Table, Fraction of Water/Vegetation)?

Delta Field Sites

DDB Childhood HomeDDB Birth Place

Five Contrasting Study Sites

Drained Peatland Pasture, BAU

Seasonally-Flooded, Rice,Agricultural OptionNewly Restored, Wetland 15 Year Old,

Restored Wetland

Corn, BAU

Mean Diurnal Pattern of CO2 Exchange, Summer 2012

• Drainage & Disturbance by Restoration

• Promote Dark Respiration

• Flooding of Rice and the Older

• Wetland Suppresses Respiration

• Photosynthesis of C4 Corn out paces C3 Photosynthesis of Rice and Wetlands

• Ranking of Carbon Sequestration Potential: Wetland > Rice > Corn

Days 200 to 250, 2012

Hours

0 4 8 12 16 20 24

FC

O2

mol

m-2

s-1

-25

-20

-15

-10

-5

0

5

10

15

Older Wetland (1997): -5.75 gC m-2 d-1

Newly Restored Wetland (Fall, 2010): -2.07 gC m-2 d-1

Rice: -4.78 gC m-2 d-1

Corn: -3.51 gC m-2 d-1

Carbon Sink Strength of Wetland Increases with Time since Restoration

C Fluxes Depend on Percent of Open Water in Fetch

Newly Restored Wetland (Fall, 2010)

Day

0 50 100 150 200 250 300 350

FC

O2 (

gC m

-2 d

-1)

-12

-10

-8

-6

-4

-2

0

2

4

2011: -53 gC m-2 y-1

2012: -368 gC m-2 y-1

190 195 200 205 210 215 220 225 230 235-25

-20

-15

-10

-5

0

5

10

15

20

Day

FC

O2

mol

m-2

s-1

Restored Wetland Experiences Weekly Oscillations in Nocturnal Respiration, unlike Other Ecosystems

A Challenge for Gap Filling and Modeling if the Excursions represent C Losses non-Local in Time or

Due to Change in Wind Direction and Fetch

Wetland Restoration Project, Mayberry Slough

Seasonal Variation in CO2 Exchange of Rice and Newly Restored Wetland

• Management of Rice can Cause Pulses of Carbon• Seed Harvest Switches a C Sink to a Source

• Rice has a Shorter Effective C Sink Period than an Established Wetland• But, C Fluxes of a Restored Wetland Will Depend on Wind Direction and Fetch

2012

Day

0 50 100 150 200 250 300 350

FC

O2

(gC

m-2

d-1

)

-12

-10

-8

-6

-4

-2

0

2

4

6

8

Rice: -24 gC m-2 y-1

Newly Restored Wetland (Fall, 2011): -234 gC m-2 y-1

Days 200 to 250, 2012

Hour

0 4 8 12 16 20 24

FC

H4 (

nmol

m-2

s-1

)

0

50

100

150

200

250

300

350

Older Wetland (1997)Newly Restored Wetland (Fall, 2010)Rice

Older Wetlands are Profligate Methane Sources!Methane Production from Rice on Peat Soils < than Rice on Clays

2011

Day

0 50 100 150 200 250 300 350

FC

H4

(mgC

m-2

d-1

)

0

50

100

150

200

250

300

350

Rice: 5.6 gC m-2 y-1

Newly Restored Wetland (Fall, 2011): 13.8 gC m-2 y-1

Rice, on peat, is a Smaller Methane Source than, Non-Tidal, Freshwater, Restored Wetlands

Low O2 in Water Promotes High Methane Fluxes

Daily Averages

0 1 2 3 4 5 6 7 80

50

100

150

200

250

300

350

400

FC

H 4 nm

ole

m-2

s-1

DO water, mg/L

older wetland

restored wetland

rice

Newly Restored + Older Wetland + Rice

Shallow Water (< 10 cm) under Rice is Warmer, More Convective and more Oxygenated, Inhibiting Methane Loss compared to non-Tidal, Older Wetland

with Deeper and Colder Water (~ 35 cm)

O2 mg/L

T wat

er

FCH

4

, nmol m-2 s-1

0 1 2 3 4 5 6 7 8

14

16

18

20

22

24

26

28

0

20

40

60

80

100

120

140

160

180

200

Conclusions

• Restored Wetlands can be Effective Carbon Sinks– Only, Several Years after Establishment– But, they can produce Huge Amounts of Methane

• Rice and Corn have Large Photosynthetic Potential, and Flooding Inhibits Soil Respiration, compared to Corn– But, Their Effective Growing Season is Short– Carbon is Exported as Seed, Switching a C Sink to a Source– On Annual Basis, Agroecosystems are Carbon Sources that

Mine Soil C