Quantification of litter fall and estimation of nutrient release through in-situ decomposition of leaf litter from some important mangrove species for projected carbon sequestration of Indian Sundarbans

Abstract

Looking into the importance of mangrove leaf litter in regulation of sediment carbon sequestration and nutrient flux in Sundarbans ecosystem, an  experiment was conducted at Jharkhali island of Sundarbans. Leaf litter-shedding from nine dominant mangrove species were collected monthly for one year (December to November) using ‘litter traps’(1 m2) in Eco-Garden on
the bank of Herobhanga creek. Seasonal litterfall was highest in Geon (Excoecaria agallocha) (103 g m-2) followed by Keora (Sonneratia apetala) (98.5 g m-2). Kal Bain (Avicennia alba) produced the highest amount (414.37 g m-2) of total annual leaf litter followed by Kankra (Bruguiera gymnorrhiza) (410.43 g m-2). Kankra (B. gymnorrhiza), Garjan (Rhizophora mucronata) and Geon (E. agallocha) dry leaf litters contained more than 50% carbon (oven-dry basis) while litter of Avicennia group contained more nitrogen and carbon. Decomposition rates of various mangrove litters were estimated through two short-term (30 days and 52 days) in-situ experiments using mangrove leaf litter in nylon net bags (0.6 mm mesh) subjected to diurnal submergence by tidal water at Jharkhali. Decomposition experiments revealed that Geon (E. agallocha) (81±5.5%) and Taura (Aegialitis rotundifolia) (26 ± 4%) were the most susceptible and resistant litters with respect to mass loss, respectively after 30 days. The biomass retained after decomposition losses (average 45±15.2% after 30 days and 56±20.2% after 52 days) indicated the amount of carbon retained in mangrove soil and ultimately determines the carbon sequestered in soil through mangrove litterfall (approximately 0.208 Tg yr-1). The study gives important insight into contribution of different mangrove species in carbon sequestration and nutrient dynamics in mangrove ecosystem of Indian  Sundarbans.