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JCBPS; Section D; August 2015 – October 2015, Vol. 5, No. 4; 4664-4672.
E- ISSN: 2249 –1929
Journal of Chemical, Biological and Physical Sciences
An International Peer Review E-3 Journal of Sciences
Available online atwww.jcbsc.org
Section D: Environmental Sciences
CODEN (USA): JCBPAT
Research Article
Stored carbon in Above Ground Biomass of dominant
mangrove floral species in Sagar Island of Indian
Sundarbans
Sumana Bhattacharyya1, Abhijit Mitra2 and Atanu Kumar Raha1
1
Department of Forest & Environmental Science, Techno India University, Salt Lake Sector V,
Kolkata, 700091,India
2
Department of Marine Science, University of Calcutta, 35 B.C. Road, Kolkata 700019,India
Received: 26 July 2015; Revised: 7 August 2015; Accepted: 9 August 2015
Abstract: We assessed the Above Ground Biomass (AGB) and stored carbon in five
dominant mangrove floral species in Sagar Island, the largest Island in Indian Sundarbans
during July 2015. The above ground biomass was of the order Avicennia alba (35.59
tonnes/ha) > Avicennia marina (34.88 tonnes/ha) > Sonneratia apetala (31.67 tonnes/ha)
> Avicennia officinalis (11.26 tonnes/ha) > Excoecaria agallocha (9.73 tonnes/ha). The
above ground carbon was of the order Avicennia alba (15.75 tonnes/ha) > Avicennia
marina (15.13 tonnes/ha) > Sonneratia apetala (13.72 tonnes/ha) > Avicennia officinalis
(4.80 tonnes/ha) > Excoecaria agallocha (4.00 tonnes/ha). The study confirms the role of
mangroves as potential sink of carbon dioxide.
Keywords: Carbon stock, mangroves, above ground biomass (AGB)
INTRODUCTION
Mangrove ecosystems thrive along coastlines throughout most of the tropics and subtropics. These
intertidal forests play important ecological and socioeconomic roles by acting as a nutrient filter between
land and sea1, contributing to coastline protection2, providing commercial fisheries resources3 and nursery
grounds for coastal fishes and crustaceans. Tropical forests in general are a disproportionately important
component in the global carbon cycle, and are thought to represent 30-40% of the terrestrial net primary
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Abhijit Mitra et. al.
production4. Although the area covered by mangrove ecosystems represents only a small fraction of
tropical forests, their position at the terrestrial-ocean interface and potential exchange with coastal water
suggests these forests make a unique contribution to carbon biogeochemistry in coastal ocean5. The
coastal zone (<200 m depth), covering ~7% of the ocean surface6 has an important role in the oceanic
carbon cycle, and various estimates indicate that the majority of mineralization and burial of organic
carbon, as well as carbonate production and accumulation takes place in the coastal ocean6,7. The potential
impact of mangrove on coastal zone carbon dynamics has been a topic of intense debate during the past
decades in particular, the “outwelling” hypothesis, first proposed for mangroves by several researchers8,9
suggested that a large fraction of the organic matter produced by mangrove trees is exported to the coastal
ocean, where it forms the basis of a detritus food chain and thereby supports coastal fisheries. A number
of recent studies have indicated that a direct tropic link between mangrove forest production and offshore
secondary production is unlikely for many mangrove systems. Despite the large number of case studies
dealing with various aspects of organic matter cycling in mangrove systems10, there is very limited
consensus on the carbon sequestering potential of mangroves.
The present study is therefore an attempt to establish a baseline data set of the carbon content in five
dominant mangrove species in the Sagar Island of western Indian Sundarbans. Increased establishment of
tree plantations in the tropics has long been suggested as a way of reducing the rate of increase in
atmospheric CO211. As trees grow, they sequester carbon in their tissues, and as the amount of tree
biomass increases (within a forest or in forest products), the increase in atmospheric CO 2 is mitigated.
The ability of these plantations to sequester carbon has generated a lot of interest, since carbon
sequestration projects in developing nations could receive investments from companies and governments
wishing to offset their emissions of green house gases through the Kyoto Protocol’s Clean Development
Mechanism12.
An accurate estimate of carbon storage and sequestration is essential for any project related to plantation
particularly in the sector of social forestry. In context to Gangetic delta region, this is extremely important
as several Government, Non-Government Organizations and even foreign donors are participating in the
mangrove afforestation programme owing to extreme vulnerability of the system to sea level rise, erosion
and tidal surges. The rate of carbon sequestration in live tree biomass is computed by finding the
difference between the carbon stocks of a population of trees at two different ages.
MATERIALS AND METHODS
The study site is located in the western part of Indian Sundarbans, at the apex of Bay of Bengal and
locally the place is known as Beguakhali. Samplings were carried out during low tide period from 5 th to
15th July, 2015 in the intertidal mudflats of Beguakhali area. The plants in this site grew naturally since
1996 almost 20 years old. Plot size of 10 m × 10 m was selected for the study and the average readings
were documented from 15 such plots (centre coordinates 21°38'54.37" N latitude and 88°03'06.17" E
longitude). The mean relative abundance of each species was evaluated for the order of dominance of
mangrove species at the study site. The above ground biomass of individual trees in each plot was
estimated as per the standard procedure stated here and the average values of 15 plots were finally
converted into biomass of five dominant mangrove species (in tonnes) per hectare in the study area.
Above ground stem biomass estimation: The above ground (stem) biomass (AGB) for each species in
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every plot was estimated using non-destructive method in which the diameter at the breast height (DBH)
was measured with a calliper and height with Ravi’s multimeter. Form factor was determined to find out
the tree volume (V) using the standard formula given by several researchers13, 14. Specific gravity (G) was
estimated taking the stem cores, which was further converted into stem biomass (BS) as per the expression
BS = GV. The expression for V is FHπ R2, where F is the form factor, R is the radius of the tree derived
from its DBH and H is the height of the target tree. The form factor F was estimated as per the standard
procedure15.
Above ground branch biomass estimation: The total number of branches irrespective of size was
counted on each of the sample trees. These branches were categorized on the basis of basal diameter into
three groups, viz. <6 cm, 6–10 cm and >10 cm. Fresh weight of two branches from each size group was
recorded separately. Dry weight of branches was estimated using the standard equation16. Total branch
biomass (dry weight) per sample tree was determined as per the expression:
Bdb = n1bw1 + n2bw2 + n3bw3 = S nibwi
Where, Bdb is the dry branch biomass per tree, ni the number of branches in the ith branch group, bwi the
average weight of branches in the ith group and i = 1, 2, 3, . . .the branch groups. This procedure was
followed for all the five dominant mangrove species separately
Above ground leaf biomass estimation: Leaves from ten branches of (of all the three size groups)
individual trees of each species were removed. One tree of each species per plot was considered for
estimation. The leaves were weighed and oven dried separately (species wise) to a constant weight at 80 ±
50C. The leaf biomass was then estimated by multiplying the average biomass of the leaves per branch
with the number of branches in a single tree and the average number of trees per plot as per the
expression:
Ldb = n1 Lw1N1 + n2Lw2N2 + ……….n5Lw5N5
Where, Ldb is the dry leaf biomass of dominant mangrove species per plot, ni ….n5 are the number of
branches of each tree of five dominant species, Lw1 …..Lw5 are dry weight of leaves removed from ten
branches of each of the five species and N1 to N5 are the number of trees per species in the plot.
Carbon estimation: This method encompasses the direct estimation of percent carbon by a CHN
analyzer. For this, a portion of fresh sample of stem, branch and leaf from thirty trees (two
trees/species/plot) of individual species (covering all the 15 plots) was oven dried at 700C, randomly
mixed and ground to pass through a 0.5 mm screen (1.0 mm screen for leaves). The carbon content (in %)
was finally analyzed on a LECO® CHN-600 analyzer.
RESULTS AND DISCUSSION
The biomass and productivity of mangrove forests have been studied mainly in terms of wood production,
forest conservation, and ecosystem management17-22. The contemporary understanding of the global
warming phenomenon, however, has generated interest in the carbon-stocking ability of mangroves. The
carbon sequestration in this unique producer community is a function of biomass production capacity,
which in turn depends upon interaction between edaphic, climate, and topographic factors of an area.
Hence, results obtained at one place may not be applicable to another. Therefore region based potential of
different land types needs to be worked out. In the present study, the results obtained have been compared
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with other regions of the world to evaluate the role of Indian Sundarbans mangrove as carbon sink on the
background of changing scenario of the climate.
Relative abundance
Eight species of true mangroves were documented in the selected plots. The mean order of abundance of
these species was Avicennia alba (23.33%) > Avicennia marina (20.00%) > Excoecaria agallocha
(16.66%) > Sonneratia apetala (13.33%) = Avicennia officinalis (13.33%) > Acanthus ilicifolius (6.66%)
> Aegiceros corniculatum (3.33%) = Bruguiera gymnorhiza (3.33%) (Table 1). Few mangrove associate
floral species (like Porteresia coarctata, Suaeda sp. etc.) were also documented in the plots, but on the
basis of relative abundance of the true mangrove species, only five dominant species namely, Avicennia
alba, Avicennia marina, Excoecaria agallocha , Sonneratia apetala, and Avicennia officinalis were
considered for carbon stock estimation in their respective above ground biomass.
Table 1: Relative abundance of mangrove species (mean of 15 plots) in the study area
Species
No./100m2
Relative abundance (%)
Sonneratia apetala
4
13.33
Excoecaria agallocha
5
16.66
Avicennia alba
7
23.33
Avicennia marina
6
20.00
Avicennia officinalis
4
13.33
Acanthus ilicifolius
2
6.66
Aegiceros corniculatum
1
3.33
Bruguiera gymnorrhiza
1
3.33
Above ground stem biomass: The above ground stem biomass of the dominant mangrove trees were
19.79 t ha-1, 5.83 t ha-1, 20.22 t ha-1, 21.14 t ha-1, and 6.70 t ha-1 for Sonneratia apetala, Excoecaria
agallocha, Avicennia alba, Avicennia marina, and Avicennia officinalis respectively (Table 2). These
values are comparatively lesser to the data of Komiyama et al 23 in a secondary mangrove (Ceriops tagal)
forest at Southern Thailand. The stem biomass formed 62.49%, 59.92%, 56.81%, 60.61% and 59.50% of
the total above ground biomass of Sonneratia apetala, Excoecaria agallocha, Avicennia alba, Avicennia
marina and Avicennia officinalis respectively.
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Above ground branch biomass: The above ground branch biomass of the dominant mangrove trees
were 7.92 t ha-1, 2.56 t ha-1, 9.91 t ha-1, 8.67 t ha-1, and 3.15 t ha-1 for Sonneratia apetala, Excoecaria
agallocha, Avicennia alba, Avicennia marina, and Avicennia officinalis respectively (Table 2). These
values are much less to the branch biomass value in a secondary mangrove (Ceriops tagal) forest at
Southern Thailand as documented by Komiyama et al (2000)24. The branch biomass constituted 25.01%,
26.31%, 27.84%, 24.86%, 27.98% of the total above ground biomass of Sonneratia apetala, Excoecaria
agallocha, Avicennia alba, Avicennia marina, and Avicennia officinalis respectively.
Above ground leaf biomass: The leaf biomass in the study site was 3.96 t ha -1 for Sonneratia apetala,
1.34 t ha -1 for Excoecaria agallocha, 5.46 t ha-1 for Avicennia alba, 5.07 t ha-1 for Avicennia marina, and
1.41 t ha-1 for Avicennia officinalis (Table 2), which are comparatively lesser to the records of other
workers like 12.1 -15.0 t ha-1 in Avicennia forests25, 6.2 – 20.2 t ha-1 in Rhizophora apiculata young
plantations26, 13.3 t ha-1 in Rhizophora patch27 and 8.1 t ha-1 in a matured Rhizophora forest18. In context
to Indian mangrove system, the mangrove litter production was recorded as 7.50 tonnes/ha/yr in
Pichavaram at Tamil Nadu28, in which leaf biomass amounts to about 80 – 90%29. Our results are lower
than the Pichavaram mangrove ecosystem in the east coast of India, which may be attributed to the trend
of rising salinity due to siltation of Bidyadhari River in the present geographical locale30. The growth,
survival, and biomass of mangroves depend on appropriate dilution of the brackish water system with
fresh water. The eastern sector of Indian Sundarbans hardly witness such dilution as the freshwater
discharge of the Ganga-Bhagirathi system cannot reach the area due to clogging of the Bidyadhari River
by heavy silt and solid wastes.
Table 2: Above ground biomass (t/ha) of five dominant mangrove species in the intertidal mudflats of
Sagar Island
Mangrove Sonneratia Excoecaria Avicennia Avicennia
vegetative
apetala
agallocha
alba
marina
part
Avicennia
officinalis
Stem
19.79
5.83
20.22
21.14
6.70
Branch
7.92
2.56
9.91
8.67
3.15
Leaf
3.96
1.34
5.46
5.07
1.41
Total (AGB)
31.67
9.73
35.59
34.88
11.26
Comparison of carbon stocks: Mangroves are unique storehouse for carbon. The global storage of
carbon in mangrove biomass is estimated to be 4.03 pg, 70% of which occurs in coastal margins from 0 0
to 100 latitude5. For the present study, the results of carbon stock in the above ground biomass of the
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selected species are shown in Table 3. Species wise carbon content are in the order Avicennia alba>
Avicennia marina> Sonneratia apetala> Avicennia officinalis > Excoecaria agallocha.
Table 3: Above ground carbon stock (t/ha) of five dominant mangrove species in the intertidal mudflats
of Sagar Island
Mangrove
vegetative
part
Sonneratia
apetala
Excoecaria
agallocha
Avicennia
alba
Avicennia
marina
Avicennia
officinalis
Stem
8.91
2.43
9.39
9.63
3.08
Branch
3.23
1.05
4.31
3.68
1.24
Leaf
1.58
0.52
2.05
1.82
0.48
Total (AGB)
13.72
4.00
15.75
15.13
4.80
Considering the values of stored carbon, the CO2 equivalents per hectare for Sonneratia apetala,
Avicennia alba, Avicennia marina, Avicennia officinalis and Excoecaria agallocha are 54.24 t,
61.58 t, 59.78 t, 19.16 t, and 16.29 t respectively, which are effective figures when the present trend of
atmospheric CO2 rise is 4% per decade31. These figures can be manipulated through effective soil
management and proper dilution of the system with freshwater, which are important requisites for
accelerating the biomass of mangrove species. The data generated in the present geographical locale are
not in alignment (in terms of magnitude) to the stored carbon in different categories of mangrove
ecosystems of Asia – Pacific region. In a Rhizophora apiculata dominated coral reef mangrove habitat
consisting of a 2 m thick mangrove peat layer in Phonpei island in Pacific, the stored carbon was
estimated as 130 Kg C m-2 (=1300 t C ha-1), and in a estuary type habitat, the value reached about 200 Kg
C m-2 as noted by a group of reseachers32.
Although the role of mangroves as sink of carbon is established through this study, but more effort
towards standardization of the techniques is needed to reach precision. Accurate measurement and
accounting for changes in carbon stores are not only important for certification and verification of carbon
credits, but would help stabilize market prices for such credit system. Inaccurate accounting or forecasting
of forest carbon stores could disrupt the market for credits, as evidenced by the recent market crash in
Europe that resulted from a lack of transparency, poor forecasting of emissions, and over allocations of
allowances33.
CONCLUSION
Mangrove forests, mostly concentrated at the land-sea interface and estuarine delta naturally sequester
carbon dioxide during photosynthesis. Over time carbon accumulates in the trees, forest- floor (in litter)
and especially soil. Approximately around 45% of the dry above ground biomass of trees is made up of
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carbon (as revealed from direct %C analysis through CHN analyzer); thus as long as the tree is growing
and accumulating biomass, it is accumulating carbon. Here we provide a comprehensive real time data on
carbon stock in a forest patch of Sagar Island in western Indian Sundarbans of 20 years old. However,
simply growing a forest or changing the way an existing forest is managed does not create forest carbon
credits. Projects must be pre-approved, baselines established, and carbon stores or changes in carbon
stocks must be determined with high precision before credits can be certified.
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* Corresponding author: Abhijit Mitra;
Department of Marine Science, University of Calcutta, 35 B.C. Road, Kolkata 700019
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