Abstract:

Evolution process of recent enviroment is usually studied by means of annual ring of tree, palynologic analysis and stable isotope assay. In this paper a new research method-biogeochemical indicator element method for study of the evolution process of recent environment is proposed. Based on researching sediments and residual plants in them from West Lake near Great Wall Station, annual rainfall variation about 4000 years and the last ice-cap melt were determined. A kind of water plants lived beneath West Lake water was identified to be Brachytheciaceae Brachythecium populeum (Hedw.)B.S.G. There are also residual plants found in the whole sediment column which is 3.4 m long. There is no obvious variation and seccession either in pattern or in structure of the plant about 4000 years, as shown by electronic microscopic observation. Ca concentration in residual plants is closely related to Ca concentration in the lake water, which are controlled by climatic condition ( mainly rainfall) . Comprehensive analysis of the sediments and residual paints in them makes us possible to suggest that the last ice-cap in this area had melted in 3500 years ago or so.