Holocene mangrove and coastal environmental changes in the western Ganga-Brahmaputra Delta, India

A 50 m-long radiocarbon dated core was studied through sediment and pollen analysis to reconstruct the Holocene mangrove and environmental changes at a coastal site Pakhiralaya in the Sundarban Biosphere Reserve in the western Ganga-Brahmaputra Delta, India. This biosphere reserve harbours a diverse mangrove ecosystem and supports a large number of people living in the area. Pollen and stratigraphic data indicate the existence of a brackish water estuarine mangrove swamp forest in this area during the last 9880 cal yr B.P. The development of the mangrove forest is not shown continuously in the Holocene record. Rapid transgression of the sea (9240 cal yr B.P.) halted the development of the mangrove. After about 8420 cal yr B.P. mangrove recolonised the area and persisted until 7560 cal yr B.P. as a result of a balance between the sedimentation and sea level fluctuation. The mangrove disappeared again from the site until 4800 cal yr B.P. because of a high sedimentation rate and possible delta progradation with loss of habitats. The reappearance of mangrove at the study site occurred with a return of a brackish water estuarine environment and the site then gradually became supra tidal during the mid-late Holocene. The continuity of the mangrove development and dynamics was interrupted by the fluctuating sea levels. Climatic fluctuations were viewed as an indirect factor influencing the mangrove ecosystem.