Journal of Sustainable Development July, 2009 125 Estimation of Methane Emission from a North-Indian Subtropical Wetland Shekhar Mallick Ecotoxicology and Bioremediation Group, Environmental Sciences Division National Botanical Research Institute (NBRI), Lucknow 226 00 (UP), INDIA E-mail: shekharm@hotmail.com Venkatesh Dutta School for Environmental Sciences (SES), Babasaheb Bhimrao Ambedkar University (Central University) Lucknow 226 025 (UP), INDIA E-mail: dvenks@gmail.com Abstract Methane emission from wetlands and its upscaling is a frontier area of research in global biogeochemical cycling including global warming. Though process based models are needed to account for variability in various types of wetland ecosystems, due to lack of required field data, it is till in infancy especially in the tropical countries. An attempt has been made through this study to estimate the quantitative and temporal variation of 4 CH emission from a subtropical wetland of North India dominated by Scirpus littoralis. A wide variation in rate of 4 CH emission was observed in an annual cycle with maximum rate reaching up to 129.82 ± 19.08 mg m -2 h -1 during March to April and negative emission rates were observed in hot and dry summer months between May to July. This finding suggests that tropical wetlands act both as source and sink of 4 CH emission depending upon the specific ecological and environmental conditions. Therefore, extrapolation of single value of rate of emission for the entire year is not correct in estimating total annual 4 CH flux. Keywords: Sub-Tropical wetlands, Methane emission, Scirpus littoralis, Carbon fixation 1. Introduction Wetlands are the areas on the landscape where land and water meet and usually lie in depressions or along rivers, lakes, and coastal waters where they are subjected to periodic flooding. Wetlands in India are distributed in various ecological regions ranging from the cold and arid zone of Laddakh through the wet Imphal and Manipur, and the warm and arid zone of Rajasthan-Gujarat to the tropical central India, and the wet humid zone of the southern peninsula. Prediction of future climatic changes and global productivity estimation depends largely on realistic assessment of green house gases from terrestrial and aquatic ecosystems with reasonable accuracy understanding the relationship between the physical environment, anthropogenic and biological activities. Wetlands, both man-made and natural are considered as one of the major contributors to atmospheric methane ( 4 CH ), and there exists complexity of processes which regulate net 4 CH flux between wetland soils and the atmosphere (Keppler & Rockmann, 2007; Chen & Prinn, 2006; Keppler, et al., 2006). There have been relatively few studies in the annual fluxes of 4 CH in lakes of subtropical regions. Recent efforts in atmospheric modelling and attempts to constrain 4 CH source strengths have indicated the need to delineate the processes responsible for the large variations in emission rates found within and across wetland types. To understand and assess the possibility and implications of temporal variations in atmospheric 4 CH , improved quantitative knowledge of 4 CH sources and sinks as well as improved estimation technique is required. Natural wetlands are responsible for approximately 76% of global methane emissions from natural sources, accounting for about 145 Tg of methane per year, while the global total 4 CH emission is estimated at ~611 Tg, giving an atmospheric lifetime for 4 CH ~8.5 yr (EPA, 2006). Next to the water vapour and carbon dioxide, 4 CH is most abundant greenhouse gas in the troposphere with an average concentration of 1.8 ppm (Keppler, et al., 2006). Its atmospheric concentration has tripled since pre-industrial times (Houghton, et al., 1996; Lelieveld, et al., 1988). Although its tropospheric concentration is rather low compared to CO 2 (~ 378 ppm) (IPCC, 2001), it is of particular importance as it is a major greenhouse gas that contributes approximately ~20% of the current total global annual emission of ~600 Tg (10 12 g). One molecule of 4 CH traps about 23-30 times more heat than CO 2 over a 100-year time scale, thus, contributing about 20% to global warming (Keppler & Rockmann, 2007; Watson, et al., 1990; Thompson & Cicerone, 1986; Ramanathan, et al., 1985).