Phytolith assemblages of core sediments and their environmental significance over the past 800 years in the Poyang Lake area, Jiangxi, China

Based on dating of Pb-210 and C-14, the core's lithology and chronology patterns have been reconstructed over the past 800 years in the Poyang Lake area, Jiangxi Province. Phytoliths were extracted from 1.5m thick core sediments, which contain silt, silty clay, and clay and meadow soil. Phytolith identification shows that there existed about 28 morphotypes mainly originating from grasses and partly from trees. Grass phytoliths are subdivided into 3 classes originating from Gramineae, Cyperaceae and Pteridophyte plants. Gramineae and Cyperaceae phytoliths are subdivided into two groups: warm type and cold type, which are likely to be the distinct signals of climatic fluctuation. Trees phytolith mainly originate from Gymnospern(conifer trees) and broadleaved plants. According to the phytolith assemblages, paleovegetation in the Poyang Lake area has undergone significant succession from zone 1to zone 9 in the last 800 years. Based on phytolith assemblages and chronology pattern, Medieval Warmth Period (zone1, 1200-1360AD), Little Ice Age (zone2-6, 1360-1880AD) and Modem Warming (zones7-9, 1880-1980AD) are identified. Our results show that phytolith assemblages also record the history of human activities characterized by index of grass cover density and percentage of gymnosperm and broadleaved trees, which might be signals of human farming and deforestation.