Pollen based vegetation and climate change records deduced from the lacustrine sediments of Kikar Tal (Lake), Central Ganga Plain, India

Abstract

A 2.0 m thick sediment profile from Kikar Tal, Raebareli District is studied for the pollen assemblage to infer the vegetation and climate variability scenario during the Holocene period. Four distinct palynozones were demarcated based on the palynological succession in the core sediment. However, the radiocarbon dates for the profile could not be procured; therefore, the lake profile is corroborated with the chronology of adjacent lake ‘Chaudhary–Ka–Tal’, Raebareli District. It is envisaged that during 8,000–7,200 cal yrs BP, (Pollen Zone KT–I), forest groves with Holoptelea, Acacia, Madhuca indica, Syzygium and Prosopis as major tree taxa were present in the adjoining area of the lake. The forest groves were interspersed with wider stretches of open vegetation comprising grasses, Tubuliflorae, Liguliflorae, Chenopodiaceae/Amaranthaceae, etc. and shrubs of Adhatoda vasica and Acanthaceae. This vegetation scenario reflects that the region was under a warm and humid climate during that time. The existence of lake is also envisaged by the presence of aquatic elements, Lemna and Typha. Subsequently, during 7,200–4,200 cal yrs BP (Pollen Zone KT–II), the forest groves became more diversified and dense in composition as evidenced by the expansion of most of the existing trees as well as presence of Emblica officinalis, Aegle, Adina cordifolia, Symplocos and Sapotaceae and thickets of Adhatoda vasica and Mimosa pudica. This significant change in the vegetation mosaic as a whole implies the initiation of a warm and more–humid climatic condition, owing to climate amelioration. The encounter of Cerealia and concomitant cropland weeds, viz. Cheno/Am. Cannabis sativa, Brassica, etc. suggests that the vicinity of the lake was under agrarian practice and other anthropogenic activities. The ground flora was still dominated by grasses; however, it also turned more profuse than before. The increasing trend of Cerealia coupled with concomitant cropland weeds signifies the augmentation in Cereal–based agrarian practice owing to favourable climatic condition. The lake expanded as manifested by the increase in aquatic elements, such as Typha, Potamogeton and Lemna during this period. During the time bracket of 4,200–1,800 cal yrs BP (Pollen Zone KT–III), the arboreals reveal a decrease in their frequency and diversity of major tree taxa with incursion of Moringa and Bombax ceiba suggesting warm and moderately humid climate with reduced monsoon. The last zone (Pollen Zone KT–IV), from 1,800 cal yrs BP–Present, elucidates open grassland vegetation corresponding to reduced monsoon precipitation, with the shrinkage of lake area. The presence of Cerealia and other culture pollen taxa suggests the prevalence of intense agrarian practice in the vicinity of the lake.