Global Journal of Environmental Science and Research ISSN: 2349-7335 Volume 3, No. 2 (April – June 2016) ABSTRACT *Corresponding author : HOW FAR THE THUMB RULE OF ESTIMATING STORED CARBON IN MANGROVES IS VALID? Arun Chakraborty 1 , Ankita Mitra 1 , Arnesha Guha 2 , Aniruddha Ray 2 , Kinsuk Purkait 2 and Abhijit Mitra 3 1 Center for Oceans, Rivers, Atmosphere and Land Sciences (CORAL), Indian Institute of Technology Kharagpur, Kharagpur 721302, West Bengal, India 2 Scientific and Environmental Research Institute, 42 Station Road, Rahara, Kolkata 700118, India 3 Department of Marine Science, University of Calcutta, 35 B.C. Road, Kolkata, West Bengal, India Alarmed at increasing level of carbon dioxide in the atmosphere, and persuaded that this contributes to climate change, policy makers and researchers are looking for ways to slow down or even reverse its accumulation. Trees and other vegetation of the producer community naturally remove carbon dioxide from the air during photosynthesis and store – sequester – carbon in stems, leaves, branches, barks, roots and soil. Estimates of carbon stock in forest plantations are generally based on allometric equa- tions relating either carbon or biomass to diameter at breast height (DBH). These equations are usually based on measurement of the fresh mass of each tree with sub-samples taken to determine moisture content to convert to dry weight. However, drying time and the number of sub-samples often vary between studies. Furthermore, the carbon concentration of different tree parts is rarely measured directly, but generally assumed to be 45% or 50% of dry weight. This creates discrepancies in the amount (value) of carbon stored in a particular forest ecosystem. Accurate measurement and accounting for changes in carbon stock are not only important for certification and verification of carbon credits, but would help stabilize market prices for such credit system. The present paper highlights this very important issue considering the above ground biomass of dominant mangrove species in Indian Sundarbans. The plant biomass estimation was carried out for an average of 30 trees in 15 (10 m ×10 m) plots from the intertidal mudflats of Annpur (centre coordinates 22° 11' 52"N latitude and 88° 50' 43"E longitude) in low tide condition during 5 th to 25 th January, 2016. The estimated above ground biomass and the carbon stock were of the order Avicennia alba > Avicennia marina > Sonneratia apetala > Avicennia officinalis > Excoecaria agallocha. The amount of carbon stored in the above ground biomass of the species varied significantly between direct measurement of the vegetative parts through carbon ana- lyzer and assumed value, which is 50% by weight of the dry biomass. The deviation was highest in case of leaves, followed by branches and stems. More experiments are needed to minimize the magnitude of deviation between these two techniques, as carbon credit from mangrove afforestration programme needs a strong and accurate experimental base. The study, however, confirms the role of mangroves as sink of carbon dioxide. Keywords: Above ground biomass, carbon stock, mangroves, Sundarbans. INTRODUCTION Mangrove ecosystems thrive along coastlines throughout most of the tropics and subtropics. These intertidal forests play important ecological and socio- economic roles by acting as a nutrient filter between land and sea (Robertson & Phillips 1995), contribut- ing to coastline protection (Vermatt & Thampanya 2006), providing commercial fisheries resources (Constanza et al. 1997) 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 repre- sent 30-40% of the terrestrial net primary production (Clark et al. 2001a). Although the area covered by mangrove ecosystems represents only a small frac-