Blue Carbon stored in the seagrass
beds of the world
James W. Fourqurean, Hilary A. Kennedy, Nuria Marbà, Miguel A.
Mateo, Gary A. Kendrick and Carlos M. Duarte
9th INTECOL International Wetlands Conference
Orlando, Florida , 3-8 June 2012
• Tropical seagrass beds are among the most productive
ecosystems, rivaling agricultural crops like corn and
soybeans and coastal wetlands
• Valuable providers of ecological goods and services (most
valuable ecosystem according to Constanza et al 1997)
2
Estimates of global CO2 flux in seagrass beds
low
high
estimate of
estimate of
global
Integrated global
NCP
extent
NCP
extent
Integrated NCP
tons CO2e ha-1y-1 km2
Tg CO2e y-1 km2
Tg CO2e y-1
Mean
4.4
300000
130.7
600000
261.4
Upper 95th cl of mean
6.2
300000
185.5
600000
371.1
Lower 95th cl of mean
2.5
300000
75.9
600000
151.8
maximum
85.4
300000
739.2
600000
1478.3
For comparison, mean NCP for:
wetlands = 0.6 tons CO2e ha-1y-1
Amazon rainforest: 3.7 tons CO2e ha-1y-1
3
Duarte et al 2010 Global Biogeochem. Cycles
But what about the
value of the Blue
Carbon stored in the
system?
4
Carbon fixed in seagrass beds does not all stay in the
seagrass beds
5
Only about half of the C buried in seagrass beds
is derived from seagrass
-5
-15
1:1
-20
13
Csediment (‰)
-10
Y = -2.31 + 1.39x
SE of slope = 0.08
r2 = 0.22, p<0.001
-25
-30
-22
-20
-18
-16
-14
-12
-10
-8
-6
-4
13
Cseagrass (‰)
6
Kennedy et al 2010 Global Biogeochem. Cycles
So, how much C is stored in seagrass ecosystems?
• Measuring C storage in some seagrass
ecosystems:
• Florida Bay
• Shark Bay
• Western Mediterranean
• Literature review of C stores in seagrasses
• Estimates of the sizes of stocks and potential
fluxes of CO2 following habitat loss
7
Measuring C stored in living biomass
8
Measuring C stored in seagrass soils:
Piston corer to collect uncompressed cores
9
Need:
• volumetric
measures of Dry
Bulk Density (mass
of soil per volume)
• Carbon content of
soil (as a fraction of
mass)
– Organic matter, or
Loss on Ignition
(LOI)
– Corg
10
Trout Creek
Russell Bank
Bob Allen Keys
Nine Mile Bank
11
0
50
50
Depth (cm)
Depth (cm)
Corg generally
decreases
downcore in Florida
Bay seagrass soils.
0
100
150
100
150
200
200
Bob Allen Keys
250
0
0
250
0
Buried peats have
high Corg
1
2
3
4
0
6
5
Depth (cm)
100
150
1
2
3
4
5
6
Organic C content (% of dry wt)
Organic C content (% of dry wt)
50
50
Depth (cm)
Russel Bank
100
150
200
200
Nine Mile Bank
Trout Cove
250
250
0
1
2
3
4
5
Organic C content (% of dry wt)
0
6
1
2
3
4
5
6
Organic C content (% of dry wt)
Fourqurean et al. In Press MFR
12
0
50
50
Depth (cm)
Depth (cm)
DBD generally
increases downcore
in Florida Bay
seagrass soils.
0
100
150
200
100
150
200
Bob Allen Keys
Russel Bank
250
0
250
0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
Buried peats have
low DBD
-1
-1
Dry Bulk Density (g mL )
50
Depth (cm)
Depth (cm)
50
100
150
200
Dry Bulk Density (g mL )
100
150
200
Nine Mile Bank
Trout Cove
250
250
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
-1
Dry Bulk Density (g mL )
Fourqurean et al. In Press MFR
-1
Dry Bulk Density (g mL )
13
14
Corg is constant or increases down-core in Shark Bay
0
0
20
20
20
40
40
40
60
80
Depth (cm)
0
Depth (cm)
Depth (cm)
Southeastern sites
Southwestern sites
Northwestern sites
60
80
60
80
100
100
100
120
120
120
140
140
140
0
2
4
6
Organic C content (% of dry wt)
80
2
4
6
8
0
Organic C content (% of dry wt)
2
4
6
8
Organic C content (% of dry wt)
Fourqurean et al. In Press MFR
15
Florida Bay
n= 695
mean = 0.84 ± 0.02
median = 0.83
minimum = 0.24
maximum = 1.63
0.3
Frequency
Shark Bay
0.2
0.1
n= 247
mean = 0.75 ± 0.01
median = 0.72
minimum = 0.35
maximum = 1.18
0.3
0.2
0.1
0.0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
0.0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Dry Bulk Density (mg mL-1)
n= 695
mean = 6.28 ± 0.28
median = 5.60
minimum = 2.63
maximum = 43.78
0.3
Frequency
Dry Bulk Density (mg mL-1)
0.2
0.1
n= 247
mean = 9.11 ± 0.20
median = 8.92
minimum = 2.77
maximum = 19.09
0.3
0.2
0.1
0.0
0.0
0
2
4
6
8
10 12 14 16 18 20
+
0
2
4
6
8
LOI (%)
n= 697
mean = 2.39 ± 0.15
median = 2.05
minimum = 0.64
maximum = 22.73
Frequency
0.3
0.2
10 12 14 16 18 20
+
LOI (%)
0.1
n= 222
mean = 3.31 ± 0.10
median = 3.33
minimum = 0.21
maximum = 8.87
0.3
0.2
0.1
0.0
0.0
0
1
2
3
4
5
6
7
8
9
Corg (% of dry weight)
10
+
0
1
2
3
4
5
6
7
8
9
Corg (% of dry weight)
10
+
16
Fourqurean et al. In Press MFR
Organic C storage in soil
-1
Mg C ha
Corg stocks in top m of seagrass beds
350
F10b
300
W4b
12-2
250
11-2
431
Ninemile 2
128
200
150
116
Ninemile 1
Russell 1
Russell 2
Trout 2
Bob Allen 1
Bob Allen 2
Trout 1
F17b
100
Florida
Bay
Seagrass biomass:
Florida Bay
1.14 MgC ha-1
Shark Bay
4.75 MgC ha-1
Shark
Bay
Fourqurean et al. In Press MFR
17
There are about 18,000 km2 of seagrass beds in south Florida
A very rough estimate of carbon stored in
the top meter of seagrass soils in south
Florida:
18,000 km2 of seagrasses
594 tons CO2e ha-1
1 x 109 tons CO2e stored in the soils!
18
0
Depth (cm)
100
200
300
400
500
0
5
10
15
20
25
30
Organic C content (% of dry wt)
Mateo et al 1997 ECSS
19
Distribution of seagrass C stock data
We compiled 3640 observations from 946 distinct locations
Fourqurean et al. 2012 Nature Geoscience
20
Global distribution of seagrass soil DBD
Number of Observations
600
n=2484
mean = 1.03 ± 0.02
median = 0.92
range: 0.06 - 2.35
500
400
300
200
100
0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2
Soil Dry Bulk Density
(g mL-1)
Fourqurean et al. 2012 Nature Geoscience
21
LOI can be used to predict Corg
50
12
y = -0.21 + 0.40x
r2 = 0.87
p<0.001
Soil Corg (% of dry weight)
10
8
40
6
4
2
30
0
0
5
10
15
20
y = -0.33 + 0.43x
r2 = 0.96
p<0.001
20
10
0
0
20
40
60
80
100
LOI (% of dry weight)
Fourqurean et al. 2012 Nature Geoscience
22
Global distribution of soil Corg in
seagrass meadows
Number of Observations
1600
Reported as Corg
Estimated from LOI
1400
1200
1000
n=3561
mean = 2.0 ± 0.1
median = 1.4
range: 0 - 48.2
800
600
400
200
0
0
2
4
6
Fourqurean et al. 2012 Nature Geoscience
8
10 12 14 16 18 20 22 24
Soil Corg
(% of dry wt)
23
Number of Observations
Global estimates of seagrass soil Corg
stocks
30
Whole core inventory
Estimated from short cores
25
20
15
10
5
0
0
100 200 300 400 500 600 700 800 900
Soil Corg Storage in top meter
Fourqurean et al. 2012 Nature Geoscience
(Mg ha-1)
24
Regional estimates of Seagrass Corg
stocks
Region
Northeast Pacific
Southeast Pacific
North Atlantic
Tropical Western
Atlantic
Mediterranean
South Atlantic
Indopacific
Western Pacific
South Australia
Global Average
Living Seagrass Biomass
MgC ha-1
n
Mean ± 95%CI
n
Soil Corg
MgC ha-1
Mean ± 95%CI
5
0
50
0.97 ± 1.02
ND
0.85 ± 0.19
1
0
24
64.4
ND
48.7 ± 14.5
44
57
5
47
0
40
0.84 ±0.17
7.29 ± 1.52
1.06 ± 0.51
0.61 ± 0.26
ND
2.32 ± 0.63
13
29
5
8
0
9
150.9 ± 26.3
372.4 ± 74.5
137.0 ± 56.8
23.6 ± 8.3
ND
268.3 ± 101.7
251
2.51 ± 0.49
89
194.2 ± 20.2
Fourqurean et al. 2012 Nature Geoscience
25
Some seagrass beds rival C-rich
terrestrial forests and mangroves
Ecosystem C storage
-1
(Mg Corg ha )
1200
Living Biomass
1000
Soil Corg
800
*
*
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400
200
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Fourqurean et al. 2012 Nature Geoscience
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26
How big are Global Seagrass Blue
Carbon stores?
• 300,000-600,000 km2 of seagrasses
• Median estimate of seagrass biomass:
2.5 Mg Corg ha-1
• Median estimate of seagrass soil Corg (top meter)
139.7 Mg Corg ha-1
• Global seagrass biomass:
75.5 and 151.0 Tg C
• Global seagrass Soil Corg:
4.2 - 8.4 Pg C
(earlier estimate of salt marshes and mangrove combined is 10 Pg C
(Chmura et al 2003)
27
Reports of seagrass losses
and the rates of decline are
increasing dramatically
28
Waycott et al. 2009 PNAS
What are the consequences of
seagrass loss to global C budget??
• Seagrass loss has averaged 1.5% y-1 since the
beginning of the 20th century
• Resulting loss of seagrass biomass:
11.3 – 22.7 Tg C y-1
• Resulting loss of seagrass soil Corg (top meter)
63 – 297 Tg C y-1
• These rates are roughly 10% of total CO2 fluxes
attributable to land use change
29
Acknowledgements:
Funding for this work:
•
NSF – FCE LTER
•
NSF – Earth Systems History
•
Australian Government Caring
for our Country grant
A product of the International Blue
Carbon Science Working Group,
spearheaded by Conservation
International
30