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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)
0.0
0.2
0.4
0.6
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
0 ppt
10 ppt
4 ppt
Question 1: What effect does salinity have on methane fluxes at the ecosystem level?
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0.00
0.10
0.20
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0.50
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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0.00
0.10
0.20
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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
• 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
-1
0
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
-1
0
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
0
5
10
15
20
25
30
35
40
45
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
0 5 10 15 20 25 30 35
Dai
ly m
ean
met
hane
flux
(um
ol/m
2 /s)
0.00
0.05
0.10
0.15
0.20
Daily mean air temperature (C)
0 5 10 15 20 25 30 35
Dai
ly m
ean
met
hane
flux
(um
ol/m
2 /s)
-0.1
0.0
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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”