Carbon sequestration by mangrove forest: One approach for managing carbon dioxide emission from coal-based power plant
Introduction
As per IPCC AR5 (2014), in the past decade of 2000–2010, anthropogenic emissions of green house gases (GHGs) increased at a rate of 2.2% per year and reached up to 49 ± 4.5 Pg CO2-equivalent per year in 2010 (1 Pg = 1015 g). Same report revealed that emissions of carbon dioxide (CO2) from fossil fuel combustion and industrial processes contributed about 78% of that total GHGs emissions increase. Emissions of CO2 from thermal power plants and cement industry are matter of concern because of their growing magnitude, the resulting increase in atmospheric concentrations of CO2, the concomitant changes in climate, and the direct impact of increased atmospheric CO2 on ecosystems and energy demand (Andres et al., 2012, Ciais et al., 2013). In 2012, fossil fuel combustion as well as cement industry contribute 9.7 ± 0.5 Pg C annually to the atmosphere which is 58% over 1990 (Le Quere et al., 2013, Peters et al., 2013). Reports also state that coal from thermal power industry shares the highest percentages (43%) towards global CO2 emission while oil, gas and cement contribute the rest (Global Carbon Project, 2008). Despite decades of significant global warming, humanity is only now beginning significantly to address the reduction of CO2 emissions caused by power generation and transport (IPCC, 2007). Hence, the reduction of CO2 emissions must be humanity's paramount concern, and any cost-effective zero-carbon technology is preferable to a carbon emitting one. Strategy-makers have been developing many roadmaps to reach the carbon neutrality especially pertaining to the thermal power emission by undertaking different carbon offset projects. Biosequestration, the uptake of anthropogenic CO2 by vegetation is one of such approaches.
Tropical forests processes about six times as much carbon as the anthropogenic emission. Changes in carbon dynamics in tropical forest with 50% contribution to global terrestrial gross primary production (GPP) (Grace et al., 2001) could alter the pace of climate change (Adams and Piovesan, 2005). Storing carbon as standing forests or from harvested wood has long been recognized as an atmospheric CO2 mitigation option (also known as ‘green carbon’). As for example, Schroeder (1992) estimated that 15–36 Pg C could be stored in tropical plantations and 50–100 Pg C sequestrated on a global scale (Winjum et al., 1992). A calculation by Lehmann (2007) indicates that an equivalent of about 10% of the US fossil fuel emissions may be harvested from biomass and stored as biochar. While the literature is vast regarding regional and tree-specific studies that shows global potential of carbon storage by the forests (Ni et al., 2016), there have been no attempt to our knowledge that addresses the same issue by the coastal habitats, in particular, mangroves. Mangrove forest accounts 0.7% of tropical forest (Giri et al., 2011) and in the coastal area it could be one of the possible sinks for the anthropogenic CO2.
The Indian Sundarbans mangrove forest in the estuarine portion of the River Ganges is the largest delta on the globe (world's heritage site) and covers about 2.84% of the global mangrove area. Overall Sundarbans biosphere was found to act as a net sink of CO2 sequestering 2.79 Tg C annually and ∼96% of the sequestered carbon was stored in the live above and below ground biomass (1 Tg = 1012 g) (Ray et al., 2011, Ray et al., 2013). Given the high productivity and fast carbon sequestration rate (faster than Amazon rainforest), Sundarbans mangrove are supposed to take safe guard against the atmospheric pollution and CO2 enrichment from the point sources like thermal power plant in Kolaghat and the heavily populated metropolis of Kolkata, both being present within 150 km from the mangroves. In fact, thermal power is the largest source of power in India. There are different types of thermal power plants based on the fuel used to generate the steam such as coal, gas, and diesel. However coal is the favorite fuel for the electricity generation in countries like India (also China) where coal and lignite based power plants have approximately 50–55% of the total electric power generation capacity (Chikkatur et al., 2011, Mittal et al., 2012). Kolaghat power plant, located in eastern India is one such coal fired thermal power plant. Nevertheless, there is a gap in understanding the capacity of the Indian Sundarbans to mitigate all the CO2 emitted from the proximate thermal power plant. Given the contrasted environmental settings of these mangroves, power plant and the metropolis, a comprehensive knowledge about their atmospheric compositions, particularly CO2 system is important to develop in the context of biosequestration.
Therefore, the main objectives of this study are: (1) to compare atmospheric compositions and CO2 exchange fluxes between three different environments i.e. mangrove-power plant-metropolis, (2) to examine the need of extension of mangrove coverage to sequester CO2 emitted from a proximate thermal power plant.
Section snippets
Indian Sundarban
The study site is located in the Indian Sundarbans (21°32' - 22°40′ N; 88°05' - 89°E, Fig. 1), which is a part of the estuary associated with the river Ganges and located at land ocean boundary of northeast coast of the Bay of Bengal. The Sundarbans, largest mangrove on the globe, cover an area of 10,200 km2, of which 4264 km2 of reserved forest is located in India and remainder in Bangladesh. In 1985, the Sundarbans was included in UNESCO's list of world heritage site. In 1989, India
Micrometeorological conditions in different study sites
Micrometeorological parameters (temperature, rainfall, solar radiation, humidity and pressure) fluctuate in response to the monsoonal cycle. Climate in all three regions is characterized by the southwest monsoon (June to September), north east monsoon or post-monsoon (October to January) and pre-monsoon (February to May). 70–80% of annual rain fall occurs during the summer monsoon (south west monsoon). Annual movement of the Inter-tropical Convergence Zone (ITCZ) in this part of the world
Conclusion
In general, this study identifies mangroves as a potential coastal habitat in removing CO2 emitted in excess from the thermal power plants. The Indian Sundarbans mangrove sequesters CO2 almost at the same rate as the CO2 emission from a Kolaghat thermal power plant (∼2.80 Tg C yr −1). It is calculated that about 4328 km2 mangrove forest coverage (1.5% increase) is needed to sequester all CO2 emitted from that thermal power plant. This study would help in great extent for future planning of
Acknowledgement
The authors are thankful to the Department of Science and Technology, Ministry of Science and Technology (DST) (Sanction No. DST/IS-STAC/CO2-SR-42/08, dated 11.05.09), New Delhi for funding the research. Authors are largely indebted to the West Bengal Power development Corporation Limited (WBPDCL) for providing monthly data of coal consumption from the thermal power plant in Kolghat. Dr. Haridas Ghatak is cordially thanked for providing local logistics during field sampling in Kolaghat. Thanks
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