Marine Science
Ghosh and Banerjee, J Marine Sci Res Development 2013, S11
http://dx.doi.org/10.4172/2155-9910.S11-001
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Inter-relationship between Physico-chemical Variables and Litter
Production in Mangroves of Indian Sundarbans
Rajrupa Ghosh1* and Kakoli Banerjee2
1
2
Techno India University, Salt Lake, Kolkata-700 091, India
School of Biodiversity and Conservation of Natural Resources, Central University of Orissa, Koraput, India
Abstract
Litter production in mangrove has immense ecological importance, as it sustains both the planktonic and
detritus food webs in the aquatic phase and intertidal mudflats, respectively. The present study was undertaken
in the western and central sectors of Indian Sundarbans that are different in terms of physico-chemical variables
(particularly salinity). Litter production was higher in the western sector owing to higher diversity of mangrove species
in the selected plots. High salinity and wind action also accelerated the process of litter fall (both leaf litter and
miscellaneous litter), and hence, the peak values of total litter, leaf litter and miscellaneous litter fall (except Sagar
Island) was observed in premonsoon season, in both the western and central sectors of the study area.
Keywords: Mangrove litter; Indian Sundarbans; Salinity
Introduction
Mangroves are taxonomically diverse group of salt-tolerant,
mainly arboreal, flowering plants that grow primarily in tropical and
subtropical regions [1]. A “mangrove” has been defined as a “tree, shrub,
palm or ground fern, generally exceeding more than half a meter in
height, and which normally grows above mean sea level in the intertidal
zones of marine coastal environments or estuarine margins” [2]. The
term “mangrove” can refer to either the ecosystem or individual plants
[2]. Estimates of mangrove area vary from several million hectares
(ha) to 15 million ha worldwide [3,4]. 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 sea [5], contributing
to coastline protection [6], providing commercial fisheries resources
[7], and nursery grounds for coastal fishes and crustaceans. About
60% to 70% of the tropical coasts are covered by mangrove ecosystem.
Mangrove vegetations sustain food webs in the adjacent aquatic phase
and intertidal mudflats through litter production. Litter production is
the shedding of vegetative or reproductive plant structures. Senescence,
withering, death and other stresses, such as winds and precipitation
govern mangrove litter production. As shown in Figure 3, mangrove
litter production can vary from as low as 0.905 gm.m-2 day-1 to as high
as 1.605 gm.m-2 day-1, depending on the seasons and physico-chemical
conditions of the area. Variability in the production of litter from place
to place may be attributed to climatic conditions and other factors, e.g.
types of forest, sediment quality and available nutrients for the plant
growth. Following litter production, decomposition and mineralization
of detritus occurs, thus fertilizing the water in and around the ecosystem
with high nutrients. Microorganisms [8], invertebrates [9-11], and
fishes [12] have been reported to consume and help in mineralization.
Thus, the role of mangrove litter in spinning the estuarine food web
is beyond any debate and doubt. Quantification of litter fall through
seasons and its relationship with ambient aquatic salinity has not been
documented in the eastern part of Indian Sundarbans, although the
area is one of the most biologically productive, taxonomically diverse
and aesthetically celebrated ecosystems of Indian subcontinent, and is
the only mangrove base of the Royal Bengal Tiger (Panthera tigris tigris)
in the planet Earth.
In the present study, an attempt has been made to report the seasonal
pattern and amount of litter production in mangrove swamps of Indian
J Marine Sci Res Development Sundarbans during 2012. Common physico-chemical variables like
surface water temperature, salinity, pH, dissolved oxygen, wind speed
and rainfall were also analysed and collected from secondary source
(Indian Meteorological Department), simultaneously to determine the
influence of these variables on litter production.
Materials and Methods
Study area
The Indian Sundarbans, a Gangetic delta at the apex of Bay of Bengal,
has an area of 9630 sq. km and houses 102 islands. The western sector
of the deltaic lobe receives the snowmelt water of mighty Himalayan
glaciers after being regulated through several barrages on the way. The
central sector, on the other hand, is fully deprived from such supply
due to heavy siltation and clogging of the Bidyadhari channel in the late
15th century. The contrasting physical set up has made the mangrove
ecosystem of Indian Sundarbans, an interesting study zone in terms
of physico-chemical variables, which have great role in the growth
and survival of mangrove species. Accordingly, our sampling stations
were selected in the western and central sectors of Indian Sundarbans
(Figure 1 and Table 1), primarily on the basis of salinity.
Litter fall and physico-chemical parameters estimation
Litter fall was determined by setting 2 rectangular traps (3 m×3 m)
in all the 5 randomly selected plots (10 m×10 m) in each station. Thus,
materials were collected from 10 traps to get a representative picture
of each station. The traps were made of 1 mm mesh size nylon screen
through which rainwater can pass [13]. They were positioned above
the high tide level [14], and contents of all the 10 traps were collected
from each of the selected stations and brought to the laboratory in
every month during 2012. The collected litter was segregated into leaf
*Corresponding author: Rajrupa Ghosh, Techno India University, Salt Lake,
Kolkata-700 091, India, Tel: (+968) 2414 3582; E-mail: [email protected]
Received July 25, 2013; Accepted October 24, 2013; Published October 29, 2013
Citation: Ghosh R, Banerjee K (2013) Inter-relationship between Physico-chemical
Variables and Litter Production in Mangroves of Indian Sundarbans.J Marine Sci
Res Development S11: 001. doi: 10.4172/2155-9910.S11-001
Copyright: © 2012 Ghosh R, et al. This is an open-access article distributed under
the terms of the Creative Commons Attribution License, which permits unrestricted
use, distribution, and reproduction in any medium, provided the original author and
source are credited.
Climate Change
ISSN:2155-9910 JMSRD an open access journal
Citation:Ghosh R, Banerjee K (2013) Inter-relationship between Physico-chemical Variables and Litter Production in Mangroves of Indian
Sundarbans.J Marine Sci Res Development S11: 001. doi: 10.4172/2155-9910.S11-001
Page 2 of 4
litter and miscellaneous litter (comprised of twigs, barks, fruits, stipules
etc), dried at 80 ± 5°C, and weighed to get the proportions of major
components in the total collections. Finally, the mean weight per plot
was estimated and transformed into gm.m-2 day-1 unit.
Hydrological parameters, such as surface water temperature,
salinity, pH and dissolved oxygen were analyzed as per the standard
methodology outlined in Strickland and Parsons [15]. Data on rainfall
and wind speed were collected from the Indian Meteorological
Department of nearest monitoring station at Canning.
Results and Discussion
The mangrove ecosystem of Indian Sundarbans sustains 34 true
mangrove species and several associates, which nourish the adjacent
waterbodies and intertidal mudflats through contribution of litter and
detritus. The tidal flushing at regular interval of time washes out the
litter from the intertidal mudflats to estuarine systems (Figure 2), which
on decomposition produces nutrients (nitrate, phosphate, etc.) that
compose the biomass of phytoplankton. The total litter fall pattern in
all the sampling stations of the study area exhibited a unique seasonal
variation (Figure 3), with highest value during premonsoon (MarchJune) and lowest during monsoon (July-October). Station wise the
litter fall values (mean of three seasons) varied as per the order Henry’s
Island (1.392 ± 0.151)>Sagar South (1.343 ± 0.225)>Chemaguri (1.261
± 0.188)>Gosaba (1.152 ± 0.253)>Canning (0.942 ± 0.198).
Peaks of leaf (Figure 4) and miscellaneous (Figure 5) litter coincided
because the flowering season in Sundarbans mangrove is mostly
restricted during Premonsoon [16] (Table 2). The total litter fall peak
coincided with the period of high wind speed in Indian Sundarbans
(Figure 6). Similar pattern of litter production was reported in a
number of mangrove studies [17-20]. Leaf production was found to
be continuous throughout the study period, which suggests that the
environmental conditions are favourable for leaf emergence all year
round, and the stress does not appear to limit the leaf production in the
present geographical locale which shows that they are evergreen forests.
Total Litter fall (gm m-2 d-1)
Figure 2: Mangrove litter washed away by tidal action in the aquatic system.
1.8
Henry’s Island
1.6
1.4
1.2
Sagar South
1
0.8
Chemaguri
0.6
Gosaba
0.4
0.2
Canning
0
Premonsoon
Figure 1: Location of sampling stations.
Station
Coordinates
Postmonsoon
Figure 3: Seasonal variation of total litter fall in the sampling stations.
Salient Features
Henry’s Island (Stn.1)
88° 15΄ 24" E
21° 45΄ 24” N
Faces River Muriganga, which is a
branch of Hugli River; located in the
western sector of Indian Sundarbans.
Sagar South (Stn.2)
88° 01΄ 47" E
21° 39΄ 04” N
Situated at the confluence of River
Hugli and Bay of Bengal on the western
sector of Indian Sundarbans.
Chemaguri (Stn.3)
88° 09΄ 11” E
21° 39΄ 49” N
Located in the western part of
Indian Sundarbans and faces River
Muriganga on the eastern side.
Gosaba (Stn. 4)
88° 39΄ 46" E
22° 15΄ 45” N
Located in the Matla Riverine
stretch in the central sector of Indian
Sundarbans.
Canning (Stn.5)
88° 40΄ 36” E
22° 18΄ 37” N
Located in the upstream of River
Matla in the central sector of Indian
Sundarbans
Figure 4: Seasonal variation of leaf litter fall in the sampling stations.
Table 1: Sampling stations with coordinates and salient features.
J Marine Sci Res Development Monsoon
Climate Change
ISSN:2155-9910 JMSRD an open access journal
Citation:Ghosh R, Banerjee K (2013) Inter-relationship between Physico-chemical Variables and Litter Production in Mangroves of Indian
Sundarbans.J Marine Sci Res Development S11: 001. doi: 10.4172/2155-9910.S11-001
Page 3 of 4
across broad geographic boundaries are reported as 7 to 12 t dry weight
ha-1 yr-1 by a number of workers [20,24-28]. The litter production in the
present study area showed drastic spatial variation with lower values
in stations of Central Indian Sundarbans, which may be attributed to
lower diversity of mangrove flora in the selected plots in their sector in
comparison to western part (Table 3).
Figure 5: Seasonal variation of miscellaneous litter fall in the sampling stations.
Flowering period
Species
20th March to 15th April
Aegiceras corniculatum, Acanthus ilicifolius
31st March to 15th April
Phoenix paludosa
5th April to 20th April
Ceriops decandra
1st May to 20th May
Avicennia spp.
20th May to 5th June
Excoecaria agallocha
15th April to 5th May
Sonneratia apetala
The physico-chemical variables of the sampling stations (Table 4)
seem to exert a regulatory influence on mangrove litter production in
the present geographical locale. Significant positive correlations of litter
fall rate with wind velocity (r=0.597; p<0.05), and salinity (r=0.699;
p<0.01) were observed, which confirm the premonsoon season as the
peak season of litter fall in the study area. The premonsoon season
in this part of the subcontinent is characterized by Nor’westers and
occasional torrential rain (Figure 7), which induce the falling of leaves,
flowers and fruits and breaking of twigs contributing to total litter
production. High surface water temperature and salinity accelerate
litter fall by posing physiological stress to mangrove species, as stated
by several researchers [29,30].
Litter production in mangrove system and its transportation
to adjacent waterbodies by tidal action has immense ecological
importance, in terms of sustenance of both detritus and planktonic
food webs. Quantification of litter biomass through season is, therefore
necessary to understand the magnitude of energy flow through various
members of the trophic level in the Sundarbans mangrove ecosystem.
Source: Chaudhuri & Choudhury [16].
Table 2: Peak periods of flowering for different mangrove species of Indian
Sundarbans.
December
Species
Sagar
South
Chemaguri
Gosaba Canning
November
Henry’s
Island
Sonneratia apetala
++
++
++
+
+
Avicennia alba
++
++
++
++
++
Avicennia marina
++
++
++
++
++
Avicennia officinalis
++
++
++
++
++
Excoecaria agallocha +
+
++
++
++
Bruguiera gymnorrhiza
+
+
+
_
_
Aegiceros rotundifolia
+
+
+
_
_
Ceriops tagal
+
+
+
_
_
October
September
August
July
June
May
April
March
++ Highly abundant; + available; - absent
February
Table 3: Composition of mangrove flora in the selected stations.
January
0
2
4
6
8
10
12
14
16
18
Wind speed (in km/hr)
Month
Figure 6: Monthly average wind speed in Indian Sundarbans during 2012;
Secondary data-collected from Indian Meteorological Department.
Similar trends were also observed by a number of researchers, while
working on the mangrove systems [21,22].
In terms of biomass, the total litter fall in the study area ranges from
3.312t ha-1 yr-1 to 5.874 t ha-1 yr-1, which is more or less comparable to
other regions of the world. Twilley et al. [17] reported that the total
annual litter fall of mixed mangrove forest of Avicennia germinans,
Rhizophora mangle and Laguncularia racemosa in South Florida
was 8.68 t ha-1 yr-1 (in Fort Myers) and 7.51 t ha-1 yr-1 (at Rookery
Bay). Steinke and Charles [22] reported the total annual litter fall of
mangrove forest in the Mgeni estuary was 8.61t ha-1 yr-1. Kishimoto
et al. [23] reported that the litter fall of mangrove stands on Iriomote
Island (Japan), was 7.50 and 8.80 t ha-1 yr-1 in Rhizophora stylosa and
Bruguiera gymnorrhiza community, respectively. The annual litter fall
J Marine Sci Res Development Henry’s
Island
Sagar
South
Season
Premonsoon
34.0
26.08
8.30
4.56
1.544
Monsoon
32.9
10.02
8.05
5.98
1.186
Postmonsoon
29.9
20.10
8.10
5.13
1.447
Premonsoon
34.0
24.15
8.28
4.55
1.605
Monsoon
32.8
9.66
8.00
4.02
1.055
Postmonsoon
29.8
18.50
8.10
4.85
1.368
Premonsoon
33.7
21.80
8.28
5.13
1.417
32.5
6.59
7.99
5.81
0.996
Postmonsoon
28.0
12.48
8.04
4.93
1.370
Premonsoon
33.6
22.40
8.10
4.68
1.500
Monsoon
32.6
12.68
7.95
4.93
0.905
Postmonsoon
29.6
19.59
8.00
5.01
1.050
Premonsoon
33.8
22.01
8.10
4.85
1.200
Monsoon
32.6
9.23
7.80
5.76
0.719
Postmonsoon
28.9
18.45
7.90
5.32
0.908
Chemaguri Monsoon
Gosaba
Canning
Surface
Surface
Total
Surface water
water
DO
temperature
water
litter
(ppm)
salinity
(oC)
pH
g/m2/day
(‰)
Table 4: Monthly variation of physico-chemical variables at the sampling stations.
Climate Change
ISSN:2155-9910 JMSRD an open access journal
Citation:Ghosh R, Banerjee K (2013) Inter-relationship between Physico-chemical Variables and Litter Production in Mangroves of Indian
Sundarbans.J Marine Sci Res Development S11: 001. doi: 10.4172/2155-9910.S11-001
Page 4 of 4
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0
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Figure 7: Seasonal average rainfall in Indian Sundarbans during 2012;
Secondary data-collected from Indian.
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