PubAg

Main content area

Modern alluvial pollen distribution in Ganges–Brahmaputra–Meghna (GBM) floodplain and its paleoenvironmental significance

Author:
Kumar, Sazal, Luo, Chuanxiu, Rahman, Ananna, Thilakanayaka, Vidusanka, Khan, Md Hafijur Rahaman, Liu, Jianguo, Islam, G.M. Ariful
Source:
Review of palaeobotany and palynology 2019 v.267 pp. 1-16
ISSN:
0034-6667
Subject:
Amaranthaceae, Asteraceae, Brassicaceae, Pinus, Poaceae, Tsuga, agricultural land, alluvium, climate, dry environmental conditions, ferns and fern allies, floodplains, fungi, hydrodynamics, paleoclimatology, paleoecology, palynology, pollen, population distribution, rivers, spores, stream channels, trees, vegetation, watersheds, wind, Bangladesh, Bay of Bengal, Himalayan region
Abstract:
Research into modern alluvial pollen constitutes essential information on understanding pollen–vegetation, vegetation–climate, and vegetation distribution pattern, which in turn facilitate reconstruction of paleovegetation and paleoenvironment. However, such studies are scarce in globally renowned Ganges–Brahmaputra–Meghna (GBM) floodplain region, Bangladesh. In order to determine the main characteristics of modern alluvial pollen distributions and its relationship with corresponding vegetation and climate, 47 alluvial sediment samples were collected from GBM riverbed, and a palynological analysis was carried out. The results indicated a clear dominance of herb pollens such as Poaceae, Amaranthaceae, Brassicaceae, and Asteraceae in the GBM floodplain region, because of their uninterrupted presence in the agricultural lands along the floodplain and being high pollen producer. Among tree pollens, Pinus and Tsuga were dominant which were transported by wind and/or water from the Himalayan region indicating the regional source of pollens in the alluvium. A gradual decreasing pattern of Pinus pollens toward the Bay of Bengal may be attributed to the gradual increase in distance from the source vegetation in the Himalaya. Fern and Fungi spores were relatively higher in the upstream of the Ganges, Brahmaputra, and Surma rivers than the Meghna River region and downstream indicating relatively higher humid conditions in the upstream than downstream. Variation in palynomorphs assemblages reflects both local and regional variations in vegetation along catchments on the GBM Rivers; however, tree pollen was under-represented in the pollen spectra due to their lower pollen productivity and preservation as well as sparse abundance in the study area. Based on PCA and variation in palynomorphs it is clear that human activities and hydrodynamic effects play a principal role in alluvial pollen dispersion, although wind effects cannot be neglected. Modern palynomorphs and its relation with climate corresponded well and can be applied for paleoclimatic study; however, the dominance of only Poaceae is not solely an indicator of aridity instead indicate highly agricultural activities in this region. These findings are of critical importance in the Quaternary as well as Holocene sequence interpretation of paleoenvironment and paleovegetation in the GBM floodplain, Bangladesh.
Agid:
6428898