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    National Academy Science Letters ISSN 0250-541XVolume 35Number 3 Natl. Acad. Sci. Lett. (2012) 35:147-154DOI 10.1007/s40009-012-0046-6

    Spatial Variation in Organic CarbonDensity of Mangrove Soil in IndianSundarbans

    Abhijit Mitra, Kakoli Banerjee & SaurovSett

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  • RESEARCH ARTICLE

    Spatial Variation in Organic Carbon Density of Mangrove Soilin Indian Sundarbans

    Abhijit Mitra Kakoli Banerjee Saurov Sett

    Received: 5 March 2012 / Accepted: 19 May 2012 / Published online: 14 June 2012

    The National Academy of Sciences, India 2012

    Abstract Soils from intertidal mudflats of mangrove

    dominated Indian Sundarbans were analyzed for soil

    organic carbon, bulk density and organic carbon density

    during 2009 in two different sectors: western and eastern.

    Samplings were carried out at 12 stations in four different

    depths (0.010.10, 0.100.20, 0.200.30 and 0.300.40 m)

    through three seasons (pre-monsoon, monsoon and post-

    monsoon). High organic carbon density is observed in the

    stations of western Indian Sundarbans, which is relatively

    close to the highly urbanized city of Kolkata, Howrah and

    the newly emerging Haldia port-cum-industrial complex.

    The mangrove forest in the eastern Indian Sundarbans

    exhibits comparatively lower organic carbon density.

    Anthropogenic activities are almost negligible in this sector

    because of its location almost within the protected forest

    area. The bulk density of the mangrove soil increased with

    depth, while organic carbon and carbon density decreased

    with depth almost in all the stations. We observed signif-

    icant spatial variations in soil organic carbon and organic

    carbon density in the study area.

    Keywords Sundarban mangrove Soil organic carbon (SOC) Bulk density Organic carbon density (OCD) Spatial variation

    Introduction

    Human activities have led to considerable emissions of

    greenhouse gases [1]. In particular, for the period from 1980

    to 1989 carbon dioxide emission from fossil-fuel burning

    and tropical deforestation amounted to 7.1 billion tons of

    carbon being released a year (Table 1) [2]. Increase in

    atmospheric carbon dioxide concentration can account for

    about half of the carbon dioxide emission for this period [3].

    This has led to study the capacity of carbon sequestration in

    forests and other terrestrial and wetland ecosystems. Most

    of the studies so far available are related to forest ecosys-

    tems and crops, and there is not enough information on

    carbon sequestration potential of wetland soil. Wetlands

    provide several important ecosystem services, among which

    soil carbon sequestration is most crucial particularly in the

    backdrop of rising carbon dioxide in the present century.

    Wetlands cover about 5 % of the terrestrial surface and are

    important carbon sinks containing 40 % of SOC at global

    level [4]. Estuarine wetlands have a capacity of carbon

    sequestration per unit area of approximately one order of

    magnitude greater than other systems of wetlands [5] and

    store carbon with a minimum emission of greenhouse gases

    due to inhibition of methanogenesis because of sulphate [6].

    The reservoirs of SOC, however, can act as sources or sinks

    of atmospheric carbon dioxide, depending on land use

    practices, climate, texture and topography [710].

    Vertical patterns of SOC can contribute as an input or

    as an independent validation for biogeochemical models

    and thus provide valuable information for examining

    the responses of terrestrial ecosystems to global change

    [1113]. A large number of biogeochemical models, how-

    ever, do not contain explicit algorithms of below-ground

    ecosystem structure and function [14]. Most of the studies

    primarily focused on the topsoil carbon stock, and carbon

    A. Mitra (&) S. SettDepartment of Marine Science, University of Calcutta,

    35 B.C. Road, Kolkata, West Bengal 700 019, India

    e-mail: abhijit_mitra@hotmail.com

    K. Banerjee

    School for Biodiversity and Conservation of Natural Resources,

    Central University of Orissa, Landiguda, Koraput 764020, India

    123

    Natl. Acad. Sci. Lett. (MayJune 2012) 35(3):147154

    DOI 10.1007/s40009-012-0046-6

    Author's personal copy

  • dynamics in deeper soil layers and driving factors behind

    vertical distributions of soil organic carbon remain poorly

    understood [11, 15, 16]. Thus, improved knowledge of dis-

    tributions and determinants of SOC across different soil

    depth is essential to determine whether carbon in deep soil

    layers will react to global change and accelerate the increase

    in atmospheric carbon dioxide concentration [16, 17].

    With this background the present study was undertaken to

    estimate the SOC in four different depths in the mangrove

    dominated Indian Sundarbans that sustains some 34 true

    mangrove species and some 62 mangrove associate species

    [18]. This deltaic lobe together with Bangladesh Sundarbans

    constitutes the worlds largest brackish water wetland. Hence

    it is essential to establish a base line data of soil carbon pool of

    this mangrove ecosystem. In this study, we used our unpub-

    lished data of SOC and bulk density to evaluate the spatial

    variations of OCD in the intertidal mudflats of western and

    eastern Indian Sundarbans that are markedly different with

    respect to anthropogenic activities and mangrove vegetation.

    Materials and Methods

    The Study Area

    The Sundarban mangrove ecosystem covering about one

    million ha in the deltaic complex of the Rivers Ganga,

    Brahmaputra and Meghna is shared between Bangladesh

    (62 %) and India (38 %) and is the worlds largest coastal

    wetland. Enormous load of sediments carried by the rivers

    contribute to its expansion and dynamics.

    The Indian Sundarbans (between 21130N and 22400Nlatitude and 88030E and 89070E longitude) is bordered byBangladesh in the east, the Hooghly River (a continuation of

    the River Ganga) in the west, the Dampier and Hodges line in

    the north, and the Bay of Bengal in the south. The important

    morphotypes of deltaic Sundarbans include beaches, mud-

    flats, coastal dunes, sand flats, estuaries, creeks, inlets and

    mangrove swamps [19]. The temperature is moderate due to

    its proximity to the Bay of Bengal in the south. Average

    annual maximum temperature is around 35 C. The summer(pre-monsoon) extends from the mid of March to mid-June,

    and the winter (post-monsoon) from mid-November to

    February. The monsoon usually sets in around the mid of

    June and lasts up to the mid of October. Rough weather with

    frequent cyclonic depressions occurs during mid-March to

    mid-September. Average annual rainfall is 1,920 mm.

    Average humidity is about 82 % and is more or less uniform

    throughout the year. This unique ecosystem is also the home

    ground of Royal Bengal Tiger (Panthera tigris tigris). The

    deltaic complex sustains 102 islands, 48 of which are

    inhabited. The ecosystem is extremely prone to erosion,

    accretion, tidal surges and several natural disasters, which

    directly affect the top soil and the subsequent carbon density.

    The average tidal amplitude is around 3.0 m.

    We conducted survey at 12 stations in the Indian

    Sundarbans region through three seasons viz. pre-monsoon

    (May), monsoon (September) and post-monsoon (Decem-

    ber) in 2009. Station selection was primarily based on

    anthropogenic activities and mangrove floral diversity.

    Because of rapid industrialization, urbanization, unplanned

    tourism, navigational, pilgrimage and shrimp culture activi-

    ties; the western Indian Sundarbans is a stressed zone (Stn.

    16). On the contrary stations 712 (in the eastern sector)

    are the areas with rich mangrove biodiversity and have been

    considered as control zone in this study. The major activi-

    ties influencing the carbon pool in the selected stations are

    highlighted in (Table 3).

    Sampling

    Table 2 and Fig. 1 represent our study site in which sam-

    pling plots of 10 9 5 m2 were considered for each station.

    Table 1 Anthropogenic carbon fluxes; 19801989 (IPCC 1994)

    GtC/year

    Carbon dioxide sources

    Fossil-fuel burning, cement production 5.5 0.5

    Changes in tropical land use 1.6 1.0

    Total anthropogenic emission 7.1 1.1

    Partitioning among reservoirs

    Storage in the atmosphere 3.2 0.2

    Oceanic uptake 2.0 0.8

    Uptake by northern hemisphere forest regrowth 0.5 0.5

    Additional terrestrial sinks: CO2 fertilization, nitrogen

    fertilization, climatic effects

    1.4 1.5

    Table 2 Sampling stations in western and eastern Indian Sundarbans

    Station Station no. Geographical location

    Longitude Latitude

    Kachuberia Stn. 1 8808004.4300 2152026.5000

    Harinbari S

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