Pollen Sedimentary Processes Of Different Lakes In Northern China

Pollen data is an important proxy for reconstructing paleo-climate and paleo-vegetation. There is perfect continuity and steady sediment velocity in Lacustrine sediment. Lacustrine pollen is a perfect proxy for investigating regional climate, environment changes, vegetation or climate model. Howevere, modern pollen process research presents pollen assemblage is influnced by vegetation condition, pollen production, dispersion, sedimentation, preservation, transmit ability, transmit agent, resedimentation process and lake size. Studies of pollen source area, transport agent, sedimentary processes and representation to vegetation within lakes are currently hot topics in palynology research.In this paper, we present results from a study of surface sediment pollen from Lake Daihai, Lake Hongjiannao, Lake Hulunnao and Lake Duikounao to explore whether pollen mixing occurs and to explore possible differences among the lakes and the characters of pollen sediment dynamics of different lakes. And investigate the difference of pollen assemblages among different sample sites and the difference among different sampling method in the same sample site by comparing pollen assenblages of traps upon water, traps under water and surface sediment samples from Lake Baiyangdian, in order to study the characters of pollen sediment dynamics of different sample types.This paper presents the pollen assemblages from 108 surface sediment samples from 4 lakes (the Lake Daihai, Lake Hongjiannao, Lake Hulunnao and Lake Duikounao) in the monsoon fringe area of China. The herb pollen taxa Artemisia, Chenopodiaceae, Poaceae and Compositae are the major components of pollen assemblages of the 4 lakes and Pinus, Betula, Quercus, Ulmus, Populus, Ostryopsis and Elaeagnaceae are frequently presented, which reflect regional and local vegetation well. The mean similarity coefficients for samples from the Lake Daihai, Lake Hongjiannao, Lake Hulunnao and Lake Duikounao are 0.66±0.17, 0.71±0.11, 0.73±0.12 and 0.67±0.12 respectively, so pollen assemblages are relatively consistent in each lake, which shows that focusing and mixing effects have occurred before and after pollen deposition. However, pollen assemblages do differ between sampling sites in each lake. The largest difference is seen in the Lake Daihai, followed by the Lake Duikounao, Lake Hulunnao and Lake Hongjiannao (The mean Euclidean distance is 20.09±11.11, 11.22±3.64, 10.67±4.03 and 8.44±4.51 respectively). These differences are possibly caused by the differences of focusing and mixing effects, pollen source areas, drainage areas and regional vegetation compositions. The Lake Daihai and Lake Hongjiannao have water deeper than 5 m and strong re-suspension, focusing and mixing effects occur in the lakeshore and shallow water areas, where pollen concentrations are lower than in deeper lake areas. In the Lake Hulunnao and Lake Duikounao, with depths less than 5 m, re-suspension and mixing effects are obvious across the whole lake area, so pollen assemblages and pollen concentrations are more consistent among sampling sites in each lake. Comparison between the lake samples and samples from the inflowing river reveals that wind is primary pollen transportation force in the Lake Hongjiannao, where the consistency of pollen assemblage is conspicuous, while there is greater variation in lakes where pollen input is dominated by waterborne sources.Pollen assemblages and pollen influxes of traps upon water, traps under water and surface sediment samples from Lake Baiyangdian show that there is consistency of pollen assemblages among different sampling methods, including hydrophyte pollen taxa (Typha, Phragmites, Myriophyllum, Potamogeton, Cyperaceae, etc.), local pollen taxa (Gramineae, Artemisia, Chenopodiaceae, Humulus, Urtica, etc.) and regional pollen taxa (Pinus, Betula, Quercus, Elaeagnaceae, Ostryopsis, etc.). Pollen assemblages from different sampling methods reflect regional and local vegetation well respectively. Pollen influxes of traps upon water are lower than traps under water obviously, which is related to the differences of pollen preservation, pollen source approach and re-suspension of water, which may indicate that there is about 91% of total pollen transported through water in Lake Baiyangdian. Distinguish analysis shows that there is preferable mixing effects when pollen was transported and sedimented through air and water, and the difference of pollen assemblage among different sample types is more obvious than among different sample sites.