Assessment of methane and nitrous oxide flux from
mangroves along Eastern coast of India
R. CHAUHAN
1
, AL. RAMANATHAN
1
AND T. K. ADHYA
2
1
School of Environmental Sciences, Jawaharlal Nehru University, New Delhi – 110067;
2
Central Rice Research Institute,
Cuttack, Orissa
ABSTRACT
Mangroves are considered to be a minor source of greenhouse gases (CH
4
and N
2
O) in pristine environmental
condition. However, estimates of efflux suggest that anthropogenic activities have led to a pronounced increase
in greenhouse gas emission. Along the east coast of India, mangroves vary substantially in area, physiography
and freshwater input, which ultimately modify the biogeochemical processes operating within this ecosystem. An
attempt has here been made to elucidate the existing variation and role of climatic variability on the emission of
greenhouse gases from mangroves. The flux estimates of CH
4
and N
2
O have been quantified from Bhitarkanika
mangrove accounting for spatial and temporal (seasonal) variation. The annual rates were estimated to be
0.096 · 10
9
gCH
4
year
)1
and 5.8 · 10
3
gN
2
O year
)1
for the whole mangrove area of the east coast of India.
Upscaling these estimates yield an annual emission of 1.95 · 10
12
gCH
4
year
)1
and 1.1 · 10
11
gN
2
O year
)1
from worldwide mangrove areas. The influence of elevated nutrient inputs through anthropogenic influence
enhances the emission of greenhouse gas. The present article shows the need to develop an inventory on green-
house gas flux from mangrove ecosystem.
Key words: emission, greenhouse budget, mangrove, methane, nitrous oxide
Received 1 September 2008; accepted 24 September 2008
Corresponding author: AL Ramanathan, School of Environmental Sciences, Jawaharlal Nehru University,
New Delhi–110067.
Email: alrjnu@gmail.com. Tel: +91 011 26704314. Fax: +91 011 26747502.
Geofluids (2008) 8, 321–332
INTRODUCTION
Mangroves are highly fragile and complex ecosystem,
which lie within the (deltaic and estuarine) transitional
zone between land and ocean, with atmosphere as a med-
ium for the exchange of matter and energy. The structure
and function of mangrove forests vary in relation to global,
regional, and local levels over different time scales. At the
global level, mangroves are ultimately limited by tempera-
ture but at the regional level, the area and biomass of man-
grove forests vary in relation to rainfall, tides, waves and
rivers. The stability of the mangrove is influenced by salin-
ity, soil type and chemistry, nutrient content and dynamics,
physiological tolerance, predation and competition at local
level (Smith et al. 2003). These tropical ecosystems are
highly productive, with high rates of organic matter trans-
formation. These physical–biogeochemical exchanges influ-
ence atmospheric chemistry through the transfer of
biogenic trace gases and sea-salt aerosols to the atmosphere
(Howarth 1998).
Methane (CH
4
) and nitrous oxide (N
2
O) are biogenic
trace gases, which are released to the atmosphere during a
series of microbial transformation processes. CH
4
is
released during the terminal step of mineralization of
organic matter (Ferry 1992), while N
2
O is produced dur-
ing nitrification as well as denitrification process (Middel-
burg et al. 1996). These gases directly or indirectly affect
the present day climate of the Earth (IPCC (Intergovern-
mental Panel on Climate Change) 2001; WMO (World
Meteorological Organization) 2003). CH
4
is the most
abundant greenhouse gas after water vapour and CO
2
, and
currently increasing at an alarming rate of 0.7% each year
(Khalil et al. 2002). The increase in atmospheric CH
4
con-
centration has induced positive radiative forcing that
amounts to about 30% of that of CO
2
(IPCC (Inter-
governmental Panel on Climate Change) 2001). The
Geofluids (2008) 8, 321–332 doi: 10.1111/j.1468-8123.2008.00227.x
 2008 The Authors
Journal compilation  2008 Blackwell Publishing Ltd

anthropogenic release of nitrogenous products to coastal
sediments enhances microbial nitrogen metabolism,which
apparently increases the N
2
O flux (Corredor & Morell
1994; Bange et al. 1996; Alongi 2002).
Mangrove ecosystem can alternatively act as both the
source and sink for a particular greenhouse gas (Mukho-
padhyay et al. 2002). The fluxes have been found to vary
geographically, based on the localized variations in natural
factors such as temperature, salinity, concentration gradi-
ent, and ultimately, the organic carbon or nitrogen content
of ecosystems (Allen et al. 2007). Additionally, several
human-induced factors, such as disposal of sewage and
agricultural runoff into these ecosystems, further enhance
trace gas emission to the atmosphere (Corredor et al.
1999).
For Indian mangroves, most of the studies on green-
house gas fluxes have been focused on climate change (Jag-
tap et al. 2002; Sharma et al. 2006) These studies are
focused on the adaptability and response of Indian man-
grove to changing climate in terms of sea level rise,
increase in temperature and shift in precipitation pattern.
In recent years, research interest has increased substantially
towards the emission of greenhouse gas from tropical eco-
systems. An inventory of anthropogenic greenhouse gases
with the concept of ‘greenhouse gas budget’ at the regio-
nal and national levels is required to protect the global cli-
mate. Such an approach should incorporate human-
induced changes and natural biospheric sources and sinks
within coastal environments. The current flux estimates are
required as inputs to inverse atmospheric models that will
ultimately provide the basis for future contingency plans
(Upstill-Goddard et al. 2000). Up to this point of time,
no comprehensive study has been reported, which could
determine the contribution of Indian mangrove towards
global greenhouse budget.
An integrated attempt had been made here to quantify
the contribution of the mangroves from the east coast of
India towards the greenhouse gas flux. We have examined
the CH
4
and N
2
O flux from Bhitarkanika mangrove and
have attempted to reveal the complexities in controls of
flux of CH
4
and N
2
O from Indian mangrove along the
Eastern coast. Further, the flux measurements have been
upscaled from local, to regional, and finally to global levels
to yield annual global flux.
STUDY AREA
India lies in the tropical belt with a long coastline, which
hosts a variety of ecosystems. The climatic variability within
this country is chiefly governed by the Arabian Sea and
Bay of Bengal. The east coast exhibits a series of vast delta
formations while the west coast is configured by steep
slopes, rises, promontories, and drowned estuaries (Ahmed
1972, Kathiresan 2003). India has a total area of 6740 sq.
km under mangroves, which is about 5% of the world’s
mangrove vegetation (Selvam 2003). The deltaic man-
groves along the east coast accounts for 70 % of the coun-
try’s total area of mangroves (Krishnamurthy et al. 1987).
The Indian subcontinent experience two monsoons in a
year; the southwest (June-September) and northeast
(October–December) monsoons. Almost 78% of total rain-
fall occurs during southwest monsoon. We have quantified
the CH
4
and N
2
O flux from Bhitarkanika mangrove and
correlated the emission with existing literature on the other
mangroves (Sunderbans, Godavari, Pichavaram and
Muthupet) of the east coast (Table 1, Fig. 1).
Bhitarkanika mangrove
Bhitarkanika mangrove is located between 2040¢–2080¢N
latitudes and 8645¢–8750¢ E longitudes, in the deltaic
region of Brahmani and Baitarani Rivers (Chadha & Kar
1999). These mangroves receive high rainfall (1400 mm,
mostly in monsoon season), however only 2.89 % of rain-
fall contributes to the mangrove in the form of runoff
(Table 1) (Zade et al. 2005). It is the second largest man-
grove ecosystem of India with an area of 672 sq. km. It is
a mangrove area of high tidal range (1–4 m) having strong
bidirectional tidal fluxes which forms extensive, low gradi-
ent inter-tidal zones available for mangrove colonization
(Selvam 2003). It supports a rich floral diversity with about
62 species of mangrove plants (Banerjee 1984).
Other mangroves along east coast of India
Sunderbans
Sunderbans represent the largest mangrove of the world,
which lies between 2131¢–2230¢ N latitudes and 88
10¢–8951¢E longitudes, that extends over an area of 2125
sq.km (Table 1) (Selvam 2003). It lies in the estuarine
Table 1 Major characteristics of mangroves along east coast of India.
Mangrove area
Surface
area (sq. km)
Tidal
amplitude (m)
Fresh water
inflow
Rainfall
(mm)
Percentage
of runoff
over rainfall Source
Sunderbans – West Bengal 2125 4–6 Perennial 1600-1800 24.16 Zade et al. 2005
Bhitarkanika – Orissa 672 2–4 July–January 1400 2.89 Zade et al. 2005
Godavari – Andhra Pradesh 465 1.5–2 July–November 1100 8.43 Zade et al. 2005
Pichavaram – Tamil Nadu 11 0.30–1 October–December 1100 2.12 Senthilkumar, 2008
Muthupet – Tamil Nadu 68 0.40–1 October–December 1100 2.2 Krithika et al. 2008
322 R. CHAUHAN et al.
 2008 The Authors
Journal compilation  2008 Blackwell Publishing Ltd, Geofluids, 8, 321–332