Reducing Uncertainty of Greenhouse Gas Fluxes from Mississippi River Delta Wetland Projects

Guerry Holm, Jr., Brian Perez, David McWhorter, Richard Raynie, Charles Killebrew, Doug Huxley

H2O CO2 CH4 N2O

Outline of Topics

• Context of carbon in Louisiana wetlands

• Research questions

• Field results

• Future progress

Importance of coastal wetlands and carbon

Coastal wetlands are bioreactors C-export: fuels estuarine production

C-preservation: drives soil formation to adjust for sea level rise

In Miss. R Delta…imbalance toward carbon loss

Marsh type

Fresh Brackish Salt

Ver

tical

acc

retio

n (c

m y

-1)

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0.8

1.0

Carbon burial capacity: Louisiana coastal wetlands types are similar over the long-term

Mature Coastal Wetland Soils in Louisiana

Soil accretion (Cesium) 0.7 cm/yr

Soil carbon content 30 mg/cm3

C accumulation rate 200 g C/m2/yr

3 t/ac/yr CO2e

7.3 t/ha/yr CO2e

48 cores dated from Chenier and Delta Plains (Piazza et al. 2011)

Sub

ESLR

Magnitude of wetland carbon loss CO2 emissions equivalents: Louisiana at 10,000 ac/yr

Loss of annual sequestration potential missed opportunity to stem pollution from 1.2 M cars over 20 years Loss from soil 25 cm of soil = 1.1 M cars 20 years = > 20 M cars

0

200,000

400,000

600,000

800,000

1,000,000

1,200,000

1,400,000

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Equi

vale

nts C

O2

emiss

ions

(#

pas

seng

er c

ars)

Year

Soil Storage

100 cm 4.4 million cars

6,000 cars/yr

Soil erosion

1,100,000 cars

10,000 ac

25 cm

Sequestration potential lost

Impetus for carbon research

Market: • wetland carbon has monetary value,

voluntary offset markets Restoration science: • carbon established currency to

assess ecosystem productivity

Measuring wetland carbon flows serve dual purposes

Restoration Science Wetland creation What is the pace of wetland development and the flow of ecosystem services? River diversions How does diversion operation influence wetland production and respiration?

Carbon Market Perspective

Monitoring and verification is well developed for forestry, not as much for wetlands There is a need to improve the science to reduce project monitoring cost

CPRA’s Methodology for Coastal Wetland Creation (VM0024)

• 2014 CPRA’s methodology approval to develop voluntary wetland carbon projects

• Overall goal: use carbon finance to increase project penetration

• Designed for wetland creation project types that use dredged sediments

• In Louisiana, we have 25 MCY per year that can be more wisely used for wetland creation

• Nationwide, there are 200 MCY of dredged sediments each year

CPRA’s carbon research and monitoring

Research questions

1. How do carbon fluxes vary across a salinity gradient, most especially methane?

2. To what degree does river diversion operation, have an effect on wetland productivity and respiration?

3. What are carbon sequestration rates of natural and created wetlands?

Methods • Landscape level fluxes of CO2, H2O, and CH4

with eddy flux towers • Chamber comparisons with USGS, also N2O

Design helps to answer environmental, wetland age, and management factors

Factors *Salinity *Diversion Created vs Natural

Locations

Davis Pond 2 yr P. aux Chenes 1 yr Goose Point 1 yr

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10 ppt

4 ppt

Question 1: What effect does salinity have on methane fluxes at the ecosystem level?

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O N D J F M A M J J A S O N D

Met

hane

flux

(um

ol/m

2/s)

CH4 Measured CH4 Predicted

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CH4 Measured CH4 Predicted

• 2012 river discharge was low through Davis Pond

• H. Issac influenced both sites with significant flooding

• Salinity at brackish site was 8-10 ppt

• Freshwater methane flux is twice is great

Comparison of methane fluxes freshwater and brackish (2012)

P. aux Chenes 8-10 ppt

Davis Pond 0 ppt

• Study by Poffenbarger et al. 2011 developed general predictive relationship of methane flux as a function of salinity (proxy for sulfate availability)

• Data were from static chambers across a range of tidal wetland habitats

Comparison of ecosystem level fluxes with chamber fluxes across the salinity gradient

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1

2

3

0 5 10 15 20 25 30 35

Log

CH

4 ann

ual f

lux

(g/m

2 /yr)

Salinity(psu)

• Semi-continuous, ecosystem level annual budget similar magnitude

• Louisiana wetlands are close to the mean, rather than outliers

• Methane emission at freshwater site exceeds long-term burial of carbon

• Salinity may become a more cost effective proxy than GHG monitoring

Comparison of ecosystem level fluxes with chamber fluxes across the salinity gradient

Log CH4 Flux = -0.0572x + 1.4179 R² = 0.53

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1

2

3

0 5 10 15 20 25 30 35

Log

CH

4 ann

ual f

lux

(g/m

2 /yr)

Salinity(psu)

Poffenbarger et al. Study CPRA Study

Expected responses:

1. CH4: availability of iron, nitrogen,

sulfate could reduce methane emissions

2. CO2: nutrient loading could increase soil respiration and/or increase plant productivity

Objective 2: How does river diversion affect methane fluxes?

Annual comparison of methane fluxes: Davis Pond diversion effects 2012 and 2013

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D J F M A M J J A S O N D J F M A M J J A S O N D

Met

hane

flux

(um

ol/m

2/s)

CH4 Measured CH4 Predicted

2012 2013

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D J F M A M J J A S O N

Cum

mul

ativ

e di

vers

ion

disc

harg

e (m

)

2012 2013

average discharge

low discharge

Year Cumulative diversion

discharge by July (m)

Methane Annual Flux

(g/m2/yr)

Methane Annual Flux

GWP 21-25 (t CO2-e/ac/yr)

2012 21 63.0 5.4 - 6.4

2013 34 61.6 5.2 - 6.2

Diversion discharge does not have a suppressive effect on methane emissions

Continuing Research, Created Wetlands

• USGS (Krauss/Johnson) working on a multivariate analysis

• Evaluates the importance of: • salinity • water level • temperature • diversion operation

• High-freq data may be useful to build stronger relationships for ecosystem modeling and C-verification

Other covariates for predicting carbon flux

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Dai

ly m

ean

met

hane

flux

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ol/m

2 /s)

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Daily mean air temperature (C)

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Brackish MarshPoint aux Chenes

Freshwater MarshDavis Pond

Real-time carbon fluxes, Goose Point

Trajectory of soil carbon accumulation: Created wetlands

5 yr : Goose Point, Bayou Dupont 10 yr: Calcasieu 20 yr: LaBranche Wetlands

Acknowledgements

• CPRA: Rick Raynie, Chuck Killebrew, Jerome Zeringue, Kyle Graham

• USGS: Ken Krauss, Becky Moss, Nicole Cormier, Darren Johnson

• CES Field Support • LDWF • USFWS • Apache

Further information on wetland carbon initiatives

• Perspectives of methodologies and carbon project development

• Jan-Feb 2014 National Wetlands Newsletter “Coastal Blue Carbon”