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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
NCP
low estimate of global extent
Integrated NCP
high estimate of global 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
Estimates of global CO2 flux in seagrass beds
Duarte et al 2010 Global Biogeochem. Cycles
For comparison, mean NCP for: wetlands = 0.6 tons CO2e ha-1y-1 Amazon rainforest: 3.7 tons CO2e ha-1y-1
3
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
13C
seagrass (‰)
-22 -20 -18 -16 -14 -12 -10 -8 -6 -4
13C
sedim
ent (
‰)
-30
-25
-20
-15
-10
-5
Y = -2.31 + 1.39xSE of slope = 0.08
r2 = 0.22, p<0.001
1:1
Only about half of the C buried in seagrass beds is derived from seagrass
Kennedy et al 2010 Global Biogeochem. Cycles 6
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
Bob Allen Keys
Russell Bank
Nine Mile Bank
11
Organic C content (% of dry wt)
0 1 2 3 4 5 6
Dep
th (
cm
)
0
50
100
150
200
250
Organic C content (% of dry wt)
0 1 2 3 4 5 6
Dep
th (
cm
)
0
50
100
150
200
250
Trout Cove
Russel Bank
Organic C content (% of dry wt)
0 1 2 3 4 5 6
Dep
th (
cm
)
0
50
100
150
200
250
Organic C content (% of dry wt)
0 1 2 3 4 5 6
Dep
th (
cm
)
0
50
100
150
200
250
Nine Mile Bank
Bob Allen Keys
Corg generally decreases downcore in Florida Bay seagrass soils. Buried peats have high Corg
12 Fourqurean et al. In Press MFR
Dry Bulk Density (g mL-1
)
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
De
pth
(cm
)
0
50
100
150
200
250
Dry Bulk Density (g mL-1
)
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
De
pth
(cm
)
0
50
100
150
200
250
Dry Bulk Density (g mL-1
)
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6D
ep
th (
cm
)
0
50
100
150
200
250
Bob Allen Keys
Dry Bulk Density (g mL-1
)
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
De
pth
(cm
)
0
50
100
150
200
250
Russel Bank
Nine Mile Bank
Trout Cove
a
DBD generally increases downcore in Florida Bay seagrass soils. Buried peats have low DBD
13 Fourqurean et al. In Press MFR
14
Corg is constant or increases down-core in Shark Bay
Organic C content (% of dry wt)
0 2 4 6 8
Dep
th (
cm
)
0
20
40
60
80
100
120
140
Organic C content (% of dry wt)
0 2 4 6 8
Dep
th (
cm
)
0
20
40
60
80
100
120
140
Organic C content (% of dry wt)
0 2 4 6 8
Dep
th (
cm
)
0
20
40
60
80
100
120
140
Northwestern sites Southwestern sites Southeastern sites
15 Fourqurean et al. In Press MFR
Dry Bulk Density (mg mL-1
)
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
0.0
0.1
0.2
0.3
Dry Bulk Density (mg mL-1
)
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Fre
qu
en
cy
0.0
0.1
0.2
0.3
LOI (%)
0 2 4 6 8 10 12 14 16 18 20 +
Fre
qu
en
cy
0.0
0.1
0.2
0.3
LOI (%)
0 2 4 6 8 10 12 14 16 18 20 +
0.0
0.1
0.2
0.3
Corg (% of dry weight)
0 1 2 3 4 5 6 7 8 9 10 +
Fre
qu
en
cy
0.0
0.1
0.2
0.3
Corg (% of dry weight)
0 1 2 3 4 5 6 7 8 9 10 +
0.0
0.1
0.2
0.3
Florida Bay Shark Bay
n= 695mean = 6.28 ± 0.28median = 5.60minimum = 2.63maximum = 43.78
n= 697mean = 2.39 ± 0.15median = 2.05minimum = 0.64maximum = 22.73
n= 222mean = 3.31 ± 0.10median = 3.33minimum = 0.21maximum = 8.87
n= 247mean = 9.11 ± 0.20median = 8.92minimum = 2.77maximum = 19.09
n= 247mean = 0.75 ± 0.01median = 0.72minimum = 0.35maximum = 1.18
n= 695mean = 0.84 ± 0.02median = 0.83minimum = 0.24maximum = 1.63
16 Fourqurean et al. In Press MFR
Org
an
ic C
sto
rag
e i
n s
oil
Mg
C h
a-1
100
150
200
250
300
350
FloridaBay
SharkBay
Ninemile 1
Ninemile 2
Bob Allen 1
Bob Allen 2
Russell 1
Russell 2
Trout 1Trout 2
F10b
116
F17b
12-2
11-2
431
W4b
128
17 Fourqurean et al. In Press MFR
Corg stocks in top m of seagrass beds
Seagrass biomass: Florida Bay 1.14 MgC ha-1
Shark Bay 4.75 MgC ha-1
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
Organic C content (% of dry wt)
0 5 10 15 20 25 30
De
pth
(c
m)
0
100
200
300
400
500
Mateo et al 1997 ECSS 19
20
Distribution of seagrass C stock data
Fourqurean et al. 2012 Nature Geoscience
We compiled 3640 observations from 946 distinct locations
Global distribution of seagrass soil DBD
Soil Dry Bulk Density
(g mL-1
)
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2
Nu
mb
er
of
Ob
se
rva
tio
ns
0
100
200
300
400
500
600
n=2484mean = 1.03 ± 0.02median = 0.92range: 0.06 - 2.35
21 Fourqurean et al. 2012 Nature Geoscience
LOI can be used to predict Corg
LOI (% of dry weight)
0 20 40 60 80 100
So
il C
org
(%
of
dry
we
igh
t)
0
10
20
30
40
50
0 5 10 15 20
0
2
4
6
8
10
12
y = -0.33 + 0.43x
r2 = 0.96p<0.001
y = -0.21 + 0.40x
r2 = 0.87p<0.001
22 Fourqurean et al. 2012 Nature Geoscience
23
Soil Corg
(% of dry wt)
0 2 4 6 8 10 12 14 16 18 20 22 24
Nu
mb
er
of
Ob
se
rva
tio
ns
0
200
400
600
800
1000
1200
1400
1600
Reported as Corg
Estimated from LOI
n=3561mean = 2.0 ± 0.1median = 1.4range: 0 - 48.2
Global distribution of soil Corg in seagrass meadows
Fourqurean et al. 2012 Nature Geoscience
Soil Corg
Storage in top meter
(Mg ha-1
)
0 100 200 300 400 500 600 700 800 900
Nu
mb
er
of
Ob
se
rva
tio
ns
0
5
10
15
20
25
30
Whole core inventory
Estimated from short cores
Global estimates of seagrass soil Corg stocks
24 Fourqurean et al. 2012 Nature Geoscience
Regional estimates of Seagrass Corg stocks
Region
Living Seagrass Biomass
MgC ha-1
Soil Corg
MgC ha-1
n Mean ± 95%CI n Mean ± 95%CI
Northeast Pacific 5 0.97 ± 1.02 1 64.4
Southeast Pacific 0 ND 0 ND
North Atlantic 50 0.85 ± 0.19 24 48.7 ± 14.5
Tropical Western
Atlantic 44 0.84 ±0.17
13 150.9 ± 26.3
Mediterranean 57 7.29 ± 1.52 29 372.4 ± 74.5
South Atlantic 5 1.06 ± 0.51 5 137.0 ± 56.8
Indopacific 47 0.61 ± 0.26 8 23.6 ± 8.3
Western Pacific 0 ND 0 ND
South Australia 40 2.32 ± 0.63 9 268.3 ± 101.7
Global Average 251 2.51 ± 0.49
89 194.2 ± 20.2
25 Fourqurean et al. 2012 Nature Geoscience
Some seagrass beds rival C-rich terrestrial forests and mangroves
Ec
os
ys
tem
C s
tora
ge
(Mg
Co
rg h
a-1
)
0
200
400
600
800
1000
1200
**
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*
*
*
*
*
*
*
*
*
**
*
*
*
*
*
**
**
**
*
*
**
****
*
*
*
**********************
************
***
**
Boreal
Tempera
te
Tropic
al
Upland
Oceanic
Mangro
ve
Seagrass
Living Biomass
Soil Corg
26 Fourqurean et al. 2012 Nature Geoscience
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
Waycott et al. 2009 PNAS 28
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