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JECET; December 2017- February 2018; Sec. A; Vol.7. No.1, 016-029. E-ISSN: 2278–179X
[DOI: 10.24214/jecet.A.7.1.01629.]
Journal of Environmental Science, Computer Science and
Engineering & Technology
An International Peer Review E-3 Journal of Sciences and Technology
Available online at www.jecet.org
Section A: Environmental Science
Research Article
16 JECET; ; December 2017- February 2018; Sec. A; Vol.7. No.1, 016-029.
DOI:10.24214/jecet.A.7.1.1629.
Carbon sequestration by mangrove vegetations: A case
study from Mahanadi mangrove wetland
Sangita Agarwal1, Kakoli Banerjee2, Nabonita Pal3, Kapileswar Mallik2,
Gobinda Bal2, Prosenjit Pramanick3 and Abhijit Mitra4
1Department of Applied Science, RCC Institute of Information Technology, Beliaghata, Kolkata
700015, India 2Department of Biodiversity & Conservation of Natural Resources, Central University of Orissa,
Landiguda, Koraput, Odisha 764 021 3Department of Oceanography, Techno India University, Salt Lake Campus, Kolkata-700091, India
4Department of Marine Science, University of Calcutta, 35 B.C. Road, Kolkata 700019, India
Received: 26 October 2017; Revised: 04 December 2017; Accepted: 12 December 2017
Abstract: We conducted a survey on the true mangrove floral stem biomass and stem
carbon during July 2012 and July 2017 with the aim to estimate the rate of stored
carbon per hectare (carbon sequestration) in the Mahanadi delta complex of Odisha.
A total of 26 species were documented from the region out of which Heritiera fomes
showed the highest population density (31.12 No./m2 in 2012 and 28.81 No./m2 in
2017). Considering the total stem biomass of all the 26 true mangrove floral species,
the rate of change of biomass was observed to be 16.20 tha-1y-1, which represents
carbon sequestration of 7.34 tha-1y-1. This sequestration value generates a CO2-
equivalent of 26.94 tha-1y-1, which calls for the conservation and restoration of
mangrove stands of Mahanadi delta region to minimize CO2 level at local scale.
Keywords: Mahanadi Delta Complex, Mangrove, Carbon sequestration, biomass
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DOI:10.24214/jecet.A.7.1.01629.
INTRODUCTION
India has a total mangrove cover of ~ 4628 sq.km1 which is 0.15% of countries land area, 8% of
Asia's mangrove and 3% of the global mangrove area. The top 10 mangrove dominated states in India
are West Bengal (2097 Km2) > Gujarat (1103 Km2) > Andaman and Nicobar Islands (604 Km2) >
Andhra Pradesh and Telengana (352 Km2) > Odisha (213 Km2) > Maharashtra (186 Km2) > Tamil
Nadu (39 Km2) > Goa (22 Km2) > Kerala (6 Km2) > Karnataka (3 Km2)2.
In the east coast of India mangroves are concentrated in the Sundarban region of West Bengal,
Subarnarekha, Bhitarkanika and Mahanadi delta of Odisha, Godavari and Krishna delta of Andhra
Pradesh, Pichavaram estuary and Cauvery estuary of Tamil Nadu3. Samal and Patnaik4 reported that in
Odisha, the mangroves spread over an area of 214 sq. km. Out of the total mangrove area of the state,
Mahanadi delta covers an area of 120 sq. km. The mangrove area in the Mahanadi delta (20°15′ to
20°70′ N latitude and 87° to 87°40′E longitude) extends from south eastern boundary of Mahanadi
river to river mouth of Hansua (a tributary of Brahmani) in the north, from the north eastern end of
Mahanadi river up to Jamboo river in east. Mahanadi mangrove wetland encompasses eight forest
blocks.
The delta region enjoys tropical monsoon climate with an average annual rainfall around 1800 mm.
75% of the rainfall occurs during months of August and September, although in 2017 the monsoon
extended till end of October. There are three main seasons prevailing in the region namely
premonsoon, monsoon and postmonsoon. Cyclonic storms are common during the monsoon season
and two cyclonic peaks are observed in the region, one during May-July and the other during October-
November.
The mangrove forests of the deltaic complex serve as the base of a productive marine and estuarine
food web (Figure 1).
Figure 1: Blue-carbon centric food web in delta complex
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DOI:10.24214/jecet.A.7.1.01629.
In recent years, the region is under threat due to mushrooming of port-cum-industries and shrimp
farms in an around the mangrove forests (Figure 2).
Figure 2: Activities around Mahanadi delta complex (Map is not in scale)
The effluents from these industries and shrimp farms are discharged into the estuarine system thus
causing an adverse impact on the mangrove biodiversity as a whole3. On the basis of this background,
the present paper aims to study the mangrove biomass and stored carbon in the stem region of the
selected true mangrove species that were documented during our field programme.
MATERIALS AND METHODS
Study area: Mahanadi mangrove wetland is located in Kendrapara district between 20°18′ - 20°32′ N
latitude and 86° 41′ - 86° 48′ E longitudes in Odisha, which is a maritime state in the east coast of
India sub-continent (Figure 1). The region has dense mangrove, which extend from Hukitala Bay in
the north to Mahanadi river mouth near Paradeep port in the south.
Sampling: Simple random sampling method was used to collect the samples. Sample plots were laid
along line transects based on tidal variation in the study area. 15 random sampling plots of 10 m × 10
m were selected on the intertidal mudflats. To evaluate the stored carbon in the stem biomass, the
taxonomic diversity, population density and stem biomass of all the true mangrove floral species were
recorded. The sampling was carried out during low tide period and only the live trees with a diameter
at breast height (DBH) ≥ 5 cm were recorded.
Estimation of stem biomass: The DBH was measured at breast height, which is 1.3 m from the
ground level. It was measured by using tree caliper and measuring tape.
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Trees with multiple stems connected near the ground were counted as single individuals and bole
circumference was measured separately. Stem height was recorded by using laser based height
measuring instrument (BOSCH DLE 70 Professional model). The methodology and procedures to
estimate the stem biomass of the selected true mangrove tree species were carried out step by step as
per the VACCIN project manual of CSIR5 considering and measuring parameters like DBH, DBR
(Diameter of basal region), height of the stem, density of the stem wood and form factor. The
population density of each species was also documented to express the value of stem biomass in t ha-1.
Estimation of stem carbon: Direct estimation of percent carbon in the stem was done by Vario
MACRO elementar CHN analyzer, after grinding and random mixing the oven dried stems from 15
different sampling plots. The estimation was done separately for each species and mean values were
expressed as t ha-1.
In the combustion process (furnace at ~ 1000oC), carbon is converted to carbon dioxide; hydrogen to
water; nitrogen to nitrogen gas/ oxides of nitrogen and sulphur to sulphur dioxide. If other elements
such as chlorine are present, they will also be converted to combustion products, such as hydrogen
chloride. A variety of absorbents are used to remove these additional combustion products as well as
some of the principal elements, sulphur for example, if no determination of these additional elements
is required.
The combustion products are swept out of the combustion chamber by inert carrier gas such as helium
and passed over heated (about 600o C) high purity copper. The function of this copper is to remove
any oxygen not consumed in the initial combustion and to convert any oxides of nitrogen to nitrogen
gas. The gases are then passed through the absorbent traps in order to leave only carbon dioxide,
water, nitrogen and sulphur dioxide.
Detection of the gases can be carried out in a variety of ways including (i) a GC separation followed
by quantification using thermal conductivity detection (ii) a partial separation by GC (‘frontal
chromatography’) followed by thermal conductivity detection (CHN but not S) (iii) a series of
separate infra-red and thermal conductivity cells for detection of individual compounds.
Quantification of the elements requires calibration for each element by using high purity ‘micro-
analytical standard’ compounds such as acetanilide and benzoic acid.
Estimation of carbon sequestration: Carbon sequestration is defined as the rate of change of stored
carbon with time. In the present study, estimation of stored carbon in the stem of the selected
mangrove trees was done during July 2012 and July 2017 in the same locations. Hence the rate of
change of stored carbon in the stem biomass of the selected species (carbon sequestration) was
calculated by dividing the difference in stored carbon between years with the time factor (5 years in
this case).
RESULT
Taxonomic diversity: A total of 26 true mangrove floral species were documented from the study
area and the population density (in No./100m2) ranged from 0.17 (Lumnitzera racemosa) to 30.12
(Heritiera fomes) in 2012 and 0.06 (Lumnitzera racemosa) to 28.81 (Heritiera fomes) in 2017 as
shown in Figure 3.
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Figure 3: Taxonomic diversity of mangrove trees in Mahanadi delta region
Above Ground Stem Biomass and Carbon: A total of 26 true mangrove floral species were
documented in which the highest rate of change in biomass was observed in Avicennia officinalis
(3.85 tha-1y-1). The lowest value was observed Lumnitzera racemosa (0.03 tha-1 y-1). Also the rate of
change of stored carbon (carbon sequestration) was estimated for all the 26 species. The highest and
the lowest values were observed in Avicennia officinalis (1.73 tha-1y-1) and Lumnitzera racemosa
(1.01 tha-1y-1) respectively (Table 1, Figure 4).
Table-1: Check-list of Mahanadi delta true mangrove flora with salient features
Sl.
No. Species Identifying Character
ΔAGB/Δt
(t ha-1)
ΔAGC/Δt
(t ha-1)
1.
Aegialitis rotundifolia
Woody shrubs or small
trees with an average
height of 2.5 m
Leathery leaves arranged
alternately or spirally.
Individual flowers have
5 petals arranged in a
fused tube around the
white gamopetalous
corolla that has 5 petals
fused in short tube.
0.15 0.06
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2.
Aegiceras corniculatum
Shrub distributed in high
saline areas, bark reddish
brown with leaves
elliptical, leaf-tip
notched, cuneate at base.
Fruit green to reddish in
maturation, sharply
curved.
Fragrant white flowers,
curved yellow or pinkish
fruits in clusters.
0.35 0.16
3.
Avicennia alba
Trees are tolerant to high
salinity, pneumatophores
spongy, narrowly
pointed with slender stilt
roots.
Bark dark brown or even
black.
Leaves lanceolate to
elliptical, leaf-tip acute,
lower surface silver grey
to white; curved fruit
with relatively long
beak.
0.23 0.10
4.
Avicennia marina
Trees are tolerant to high
salinity, pneumatophores
pencil-like.
Bark yellowish brown.
Leaves elliptical, leaf-tip
rolling, lower surface
white to light grey.
Inflorescence terminal or
axillary, orange yellow
in colour.
0.99 0.46
5.
Avicennia officinalis
Trees are tolerant to high
salinity, pneumatophores
pencil-like.
Bark yellowish brown.
Leaves elliptical, leaf-tip
roundish, obtuse apex,
lower surface white to
light grey.
Inflorescence terminal or
axillary, orange yellow
in colour.
3.85 1.73
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6.
Bruguiera cylindrica
Trees can grow upto 20
m with smooth grey
bark.
The glossy, grey leaves
are opposite, simple and
elliptical with pointed
ends.
Presence of propagule.
0.07 0.03
7.
Bruguiera gymnorrhiza
Trees generally found on
elevated interior parts of
mangrove forest with
prominent buttress roots.
Bark dark grey. Leaves
simple, elliptical-oblong,
leathery and leaf-tip
acuminate.
Flowers axillary, single
with red calyx, red in
colour and almost 16
lobed; fruits are cigar
shaped, stout and dark
green.
0.09 0.04
8.
Bruguiera parviflora
Trees grow upto 30 m
with a trunk diameter
upto 0.45 m.
Presence of pale grey to
pale brown bark.
The fruits measure upto
4 cm in length.
0.04 0.02
9.
Bruguiera sexangula
The trees usually grow
as single stem tree or
multi-stem shrub.
The bark is smooth and
greyish brown in colour.
Presence of smooth,
glossy, green leaves,
which are simple and
opposite - elliptical to
elliptic –oblong.
0.07 0.03
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10.
Ceriops decandra
Stilt roots arising from
pyramidal stem base.
Light grey barked stem.
Leaves elliptic-oblong,
emarginated at apex,
cuneate at base.
Flowers axillary in
condensed cymes.
0.44 0.21
11.
Ceriops tagal
Trees upto 25 m with a
trunk diameter of upto
0.40 m.
The leaves are opposite
pairs, glossy, yellowish
green above and
obovate.
The flowers are borne
singly in the leaf axils.
0.11 0.05
12.
Excoecaria agallocha
Prominent main root
absent, many laterally
spreading snake-like
roots producing elbow
shaped pegs.
Poisonous milky latex
highly irritating to eyes.
Leaves light green with
wavy margin.
Catkin inflorescence
terminal or axillary,
orange yellow.
1.48 0.65
13.
Heritiera fomes
Trees with numerous
peg-like pneumatophores
and bind root suckers.
Young branches covered
with shining golden-
brown scales. Leaves
elliptic with lower
surface shining with
silvery scales.
Flowers golden yellow
with reddish tinge inside.
2.86 1.29
14.
Heritiera littoralis
Presence of silvery
scales on the underside
of the leaves.
Leaf blade large, silvery
white to dull and very
abruptly narrowed.
Seeds surrounded by
fibrous pericarp.
0.37 0.16
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15.
Kandelia candel
Trees with prominent
stilt roots.
Leaves narrowly
elliptical, leathery
midrib, lower leaf
surface yellowish green.
Flowers in 2 cymes on
stout peduncle; fruit
viviparous with
cotyledonary collar, red
when mature.
0.10 0.05
16.
Lumnitzera racemosa
Presence of succulent
small leaves with
obovate shape.
Fruit is fleshy and
flattened while on trees
but becomes fibrous after
floating in water.
Absence of well
developed above ground
root system.
0.03 0.01
17.
Phoenix paludosa
Palm tree like
appearance with no
aerial roots, generates
found on hard muddy
soil of mangrove
swamps.
Leaves held in crown
above the trunk, petiole
armed with hard spines.
Flowers dioecious,
yellowish white,
trimerous spadices
arising in between
leaves; Spathes about 30
cm long, enclosing the
flowers; fruit drupe,
oblong, 1 seeded, shining
black when ripe.
0.05 0.02
18.
Rhizophora apiculata
Average height of the
tree around 10 m with
grey bark.
Presence of elliptic-
oblong to sub-lanceolate
leaf blade.
Presence of sessile
flowers.
0.05 0.02
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Rhizophora mucronata
Trees upto 25 m and
have large number of
aerial stilt roots
buttressing the trunk.
Presence of elliptical
leaves with elongated
tips.
The flowers develop in
axillary clusters on the
twigs. Each flower has a
hard cream colour calyx
with 4 sepals and 4 white
hairy petals.
0.30 0.13
Rhizophora stylosa
Trees are usually around
5 m in height.
The propagules grow
upto 30 cm in length.
Presence of prominent
stilt roots.
0.29 0.13
Sonneratia alba
Trees grow upto 15 m
and sometimes even upto
25 m.
The tree is surrounded
by thick blunt
pneumatophores.
Evergreen tree with a
broad spreading crown.
1.46 0.67
Sonneratia apetala
Trees are with long,
corky, forked
pneumatophores and
stem light brown in
colour.
Leaves thick, coriaceous,
narrowly elliptic oblong
tapering towards apex.
Flowers are cream
coloured in axilliary
cymes with globose
berry seated in flattened
calyx tube.
1.58 0.74
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Sonneratia caeseolaris
Trees grow up to 20 m in
height with a trunk
diameter of 0.5 m.
Presence of apple-like
fruits.
Presence of slender
pnuematophores.
0.14 0.07
Xylocarpus granatum
Pnuematophores
completely absent. Bark
yellowish white, peeling
off as papery flakes.
Leaflets bijugate or
unijugate, obovate,
rounded apex and
tapering base.
White flowers with
reddish gland within;
large fruit with
pyramidal seeds.
0.80 0.35
Xylocarpus mekongensis
Presence of blind suckers
and plank like roots.
Bark is pale greenish or
yellowish with alternate,
elliptical to obovate,
rounded leaf tip and
tapering at base.
Flowers small, white,
axillary; fruits yellowish
brown, small ball
shaped.
0.13 0.06
Xylocarpus molluccensis
Trees grow upto 30 m
with a trunk diameter
reaching upto 0.7 m
Presence of creamy
white flowers.
Presence of round
shaped fruits measuring
up to 11 cm in diameter.
0.15 0.07
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Figure 4: Rate of change of stem biomass and stored carbon in true mangrove species of Mahanadi
delta
DISCUSSION
The rapid pace of climate change is an issue of concern in the present century, which is keenly related
to the rise of carbon dioxide. In the past 60 years the amount of carbon dioxide emitted to the
atmosphere is primarily due to the increased use of fossil fuels. This has resulted in the rise of carbon
dioxide level from pre-industrial level of 280 ppm to present level of 407.25 ppm as on July 20176.
To keep this trend stable by retarding the accelerating pace of carbon dioxide level, it is essential to
lock this gas within the vegetative sink. This process has multiple benefits like generation of wood
(for timber, fuel etc.), oxygen (which is the life jacket of human civilization), food products (like
fruits, cereals etc.). The litter/detritus produced by mangroves serves as the base of fishery by
triggering the growth of phytoplankton. This paper highlights the ecosystem benefit of Mahanadi
delta mangroves (26 true mangroves as documented in this study) in context to carbon sequestration
by the stem biomass of the species. The branch, twigs and leaf carbon has not been considered due to
conservative approach of this study, which otherwise need to be cut down for carbon estimation in
these vegetative parts. It is interesting to note that in the present study site the rate of change of true
mangrove biomass is 16.20 tha-1y-1, which represent a carbon sequestration value of 7.34 tha-1y-1. This
value is definitely an under- estimation in the domain of carbon sequestration as a major portion of the
stored carbon is locked in the branches, twigs and leaves of the mangrove trees. However, the
sequestrated carbon in the stems of selected mangrove trees represents a CO2-equivalent value of
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26.94 tha-1y-1, which means that 1 ha of the mangrove patch in Mahanadi delta region has the potential
of absorbing 26.94 tonnes of CO2 from ambient atmosphere in 1 year. Conversely, it can be concluded
that clearance of 1 ha mangrove patch in the present geographical locale may lead to an emission of
26.94 tonnes of CO2 in the ambient air. This may lead to rise of temperature at local level as pointed
out by several researchers7,8,9,10,11,12,13,14. Thus to keep an overall stability of the ecosystem,
conservation of mangrove should be given highest priority in the Integrate Coastal Zone Management
Plan (ICZMP) for the maritime state of Odisha. Threats like over exploitation of mangrove resources,
habitat destruction for tourism, shrimp culture and effluent discharge from port- cum-industrial
complex of Paradeep should be minimized so as to achieve the goal of sustainable management action
plan placing the role of mangroves as the key regulator of GHG emission in the epicentre.
ACKNOWLEDGEMENT
The authors acknowledge the financial support provided by the Ministry of Earth Sciences, Govt. of
India. The infrastructural facilities provided by the Forest Department, Govt. of Odisha are gratefully
acknowledged.
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* Corresponding Author: Sangita Agarwal
1Department of Applied Science, RCC Institute of Information Technology,
Beliaghata, Kolkata 700015, India
Date of publication on line 12.12.2017
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