Pollen assemblages and their environmental correlates during the past 200 years inferred from sediments records in a shallow lake

摘要

Pollen profiles based on sediments taken from Baiyangdian Lake were used to analyze vegetation type alternation during the past 200 years. The pollen record suggests changes occur during two different time frames. The period before 1863 showed that the climate was dry and the lake was in its adolescence, thereafter the climate turned wet and temperate. Pollen diversity, which is largely influenced by water transportation, shows that the water surface area of Baiyangdian has been shrinking. Analysis of the historical pollen-environment correlation showed LOI, C/N and silt content play more essential roles on pollen assemblages than other sediment parameters through RDA (redundancy analysis) ordination method. Meanwhile CCA (Canonical Correspondence Analysis) analysis demonstrated that water level has a closer relationship with aquatic herbaceous pollen, such as Myriophyllum and Phragmites; however, temperature is coincident with tree pollen. The richness of pollen assemblages, compared with evenness, is more likely to be affected by fluctuations of water level and temperature. Furthermore, in Baiyangdian Lake, precipitation tends to be more abundant when extreme temperature becomes lower annually.