Modern pollen distribution and its relationship to vegetation from the south-western part of the Ganges-Brahmaputra Delta, India

Thirty surface samples collected from the Pakhiralaya area, south-western Ganges-Brahmaputra Delta, India, have been analysed for pollen in order to investigate modern pollen-vegetation relationships. Data on non-pollen palynomorphs (fungal spores, dinoflagellate cysts and algal cysts) were also obtained. There is currently a paucity of modern pollen studies from this region, which places limits on the interpretation of pollen data from other types of studies, for example studies aimed at understanding the Holocene vegetation history of this globally renowned tropical forest region. The local vegetation of the area is characterised by mangrove, marsh, herb and open land. The results of our study indicate that the pollen from locally growing taxa are the major components of modern pollen assemblages. Thus, pollen spectra show close linkages between modern pollen and local vegetation. Within the samples collected from the mangrove forest, the dominant mangrove taxa (Rhizophora mucronata, Bruguiera gymnorrhiza, Excoecaria agallocha, Sonneratia and Avicennia marina) are also the most frequently encountered pollen types, along with the mangrove associate taxa Thespesia sp., Pongamia pinnata and Phoenix paludosa. Thus, undisturbed mangrove forests are characterised mainly by a dominance of true mangrove and mangrove associate species in the pollen spectra. In contrast, pollen spectra from samples from open land' areas contained significant proportions of pollen from midland taxa. Anthropogenic impact on this area is captured in the samples through pollen of introduced plants such as Eucalyptus and Casuarina equisetifolia. The present study provides a basis for useful interpretation of Late Quaternary pollen sequences from the Ganges-Brahmaputra Delta, since modern pollen studies are still meagre in the poorly investigated delta region.